diff options
author | Jeffrey H. Kingston <jeff@it.usyd.edu.au> | 2010-09-14 19:21:41 +0000 |
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committer | Jeffrey H. Kingston <jeff@it.usyd.edu.au> | 2010-09-14 19:21:41 +0000 |
commit | 71bdb35d52747e6d7d9f55df4524d57c2966be94 (patch) | |
tree | 480ee5eefccc40d5f3331cc52d66f722fd19bfb9 /doc/design | |
parent | b41263ea7578fa9742486135c762803b52794105 (diff) | |
download | lout-71bdb35d52747e6d7d9f55df4524d57c2966be94.tar.gz |
Lout 3.17.
git-svn-id: http://svn.savannah.nongnu.org/svn/lout/trunk@2 9365b830-b601-4143-9ba8-b4a8e2c3339c
Diffstat (limited to 'doc/design')
-rw-r--r-- | doc/design/README | 25 | ||||
-rw-r--r-- | doc/design/all | 58 | ||||
-rw-r--r-- | doc/design/mydefs | 591 | ||||
-rw-r--r-- | doc/design/outfile.ps | 11727 | ||||
-rw-r--r-- | doc/design/s1_0 | 45 | ||||
-rw-r--r-- | doc/design/s2_0 | 14 | ||||
-rw-r--r-- | doc/design/s2_1 | 87 | ||||
-rw-r--r-- | doc/design/s2_2 | 79 | ||||
-rw-r--r-- | doc/design/s2_3 | 326 | ||||
-rw-r--r-- | doc/design/s2_4 | 345 | ||||
-rw-r--r-- | doc/design/s2_5 | 90 | ||||
-rw-r--r-- | doc/design/s2_9 | 2 | ||||
-rw-r--r-- | doc/design/s3_0 | 10 | ||||
-rw-r--r-- | doc/design/s3_1 | 76 | ||||
-rw-r--r-- | doc/design/s3_2 | 113 | ||||
-rw-r--r-- | doc/design/s3_3 | 143 | ||||
-rw-r--r-- | doc/design/s3_4 | 51 | ||||
-rw-r--r-- | doc/design/s3_9 | 2 | ||||
-rw-r--r-- | doc/design/s4_0 | 88 | ||||
-rw-r--r-- | doc/design/s5_0 | 11 | ||||
-rw-r--r-- | doc/design/s5_1 | 123 | ||||
-rw-r--r-- | doc/design/s5_2 | 372 | ||||
-rw-r--r-- | doc/design/s5_3 | 125 | ||||
-rw-r--r-- | doc/design/s5_4 | 97 | ||||
-rw-r--r-- | doc/design/s5_5 | 109 | ||||
-rw-r--r-- | doc/design/s5_9 | 2 | ||||
-rw-r--r-- | doc/design/s6_0 | 18 | ||||
-rw-r--r-- | doc/design/s6_1 | 85 | ||||
-rw-r--r-- | doc/design/s6_2 | 79 | ||||
-rw-r--r-- | doc/design/s6_9 | 2 | ||||
-rw-r--r-- | doc/design/s7_0 | 84 |
31 files changed, 14979 insertions, 0 deletions
diff --git a/doc/design/README b/doc/design/README new file mode 100644 index 0000000..1e7a8af --- /dev/null +++ b/doc/design/README @@ -0,0 +1,25 @@ +Directory lout/doc/design + +This directory contains the Lout source files +for the report entitled `The design and +implementation of the Lout document formatting +language' which appeared in Software--Practice +and Experience, vol 23, pp1001-1041 (September +1993). To produce the report, type the command + + lout all > outfile.ps + +in this directory. This must be done three +times to completely resolve all cross references, +although the PostScript file outfile.ps is +printable after the first run. Auxiliary files +with .li and .ld suffixes will be created in +this directory. A copy of the final outfile.ps +is included. + +The second and third runs should produce no error +messages (although changing the paper size might +produce one or two benign ones). + +Jeffrey H. Kingston +17 September 1999 diff --git a/doc/design/all b/doc/design/all new file mode 100644 index 0000000..2755e5b --- /dev/null +++ b/doc/design/all @@ -0,0 +1,58 @@ +@SysInclude { eq } +@SysInclude { tab } +@SysInclude { fig } +@SysInclude { report } +@SysDatabase @Reference { oldrefs } +@Report + @Title { The Design and Implementation +of the +Lout Document Formatting Language } + @Author { Jeffrey H. Kingston } + @Institution { Basser Department of Computer Science, +The University of Sydney 2006, +Australia } + @DateLine { 27 January, 1993 } + @InitialLanguage { English } + @OptimizePages { Yes } + @AbstractTitle { SUMMARY } + @Abstract +{ +Lout is a high-level language for document formatting, whose ease of use +has permitted an unprecedented number of advanced features to be added +quickly and reliably. This paper charts the evolution of the design and +implementation of Lout from conception in mid-1984 to public release in +October 1991. It includes extensive discussions of remaining problems +and possible solutions. +@DP +{@B Keywords} document formatting typesetting +} + +// + +@Include { s1_0 } +@Include { s2_0 } +@Include { s2_1 } +@Include { s2_2 } +@Include { s2_3 } +@Include { s2_4 } +@Include { s2_5 } +@Include { s2_9 } +@Include { s3_0 } +@Include { s3_1 } +@Include { s3_2 } +@Include { s3_3 } +@Include { s3_4 } +@Include { s3_9 } +@Include { s4_0 } +@Include { s5_0 } +@Include { s5_1 } +@Include { s5_2 } +@Include { s5_3 } +@Include { s5_4 } +@Include { s5_5 } +@Include { s5_9 } +@Include { s6_0 } +@Include { s6_1 } +@Include { s6_2 } +@Include { s6_9 } +@Include { s7_0 } diff --git a/doc/design/mydefs b/doc/design/mydefs new file mode 100644 index 0000000..5473fbf --- /dev/null +++ b/doc/design/mydefs @@ -0,0 +1,591 @@ + +def @TeX { T{ /0.2fo E}X } + +def @Code + right x +{ { Helvetica Base -1p } @Font lines @Break x +} + +###################################################### +# # +# Nodes and trees. # +# # +###################################################### + +import @Fig +def @FBox + named width { 0.6c } + named height { 0.4c } + named margin { 0.1c } + right x +{ + @Box margin { margin } + { width @Wide height @High + { /0.5rt |0.5rt @OneCol @OneRow 0.8f @Font x + } + } +} + +import @Fig +def @FEllipse + named width { 0.6c } + named height { 0.4c } + named margin { 0.1c } + right x +{ + @Ellipse margin { margin } + { height @High + { /0.5rt |0.5rt @OneCol @OneRow 0.8f @Font x + } + } +} + +import @Fig +def @FCircle + named width { 0.4c } + named height { 0.4c } + named margin { 0.1c } + right x +{ + @Circle margin { margin } + { width @Wide height @High + { /0.5rt |0.5rt @OneCol @OneRow 0.8f @Font x + } + } +} + +import @Fig +def @JoinFigures + left A + named linestyle { solid } + named linewidth { 0.5 pt } + named linecap { round } + named dashlength { 0.15 cm } + named arrow { noarrow } + named headstyle { open } + named headwidth { 0.05 cm } + named headlength { 0.15 cm } + right B +{ + @Line + from { {A"@CTR"} ++ {{A"@CTR"} @Angle {B"@CTR"} A"@CIRCUM"} } + to { {B"@CTR"} ++ {{B"@CTR"} @Angle {A"@CTR"} B"@CIRCUM"} } + linestyle { linestyle } + linewidth { linewidth } + linecap { linecap } + dashlength { dashlength } + arrow { arrow } + headstyle { headstyle } + headwidth { headwidth } + headlength { headlength } + {} +} + +import @Fig +export @LeftSub @RightSub @FirstSub @NextSub @StubSub @Node +def @Tree + named hmargin { 0.2c } + named vmargin { 0.3c } + named linestyle { solid } + named linewidth { 0.5 pt } + named linecap { round } + named dashlength { 0.15 cm } + named arrow { noarrow } + named headstyle { open } + named headwidth { 0.05 cm } + named headlength { 0.15 cm } + body x +@Begin + + def @LeftSub + precedence 90 + associativity left + left root + named hmargin { hmargin } + named linestyle { linestyle } + named linewidth { linewidth } + named linecap { linecap } + named dashlength { dashlength } + named arrow { arrow } + named headstyle { headstyle } + named headwidth { headwidth } + named headlength { headlength } + right x + { + { /vmargin {L::x} } |hmargin root | + L@T @JoinFigures + linestyle { linestyle } + linewidth { linewidth } + linecap { linecap } + dashlength { dashlength } + arrow { arrow } + headstyle { headstyle } + headwidth { headwidth } + headlength { headlength } + T + } + + def fixroot + precedence 90 + left root + { + |0.5rt root + } + + def firstsub + precedence 90 + associativity left + named hmargin { hmargin } + named linestyle { linestyle } + named linewidth { linewidth } + named linecap { linecap } + named dashlength { dashlength } + named arrow { arrow } + named headstyle { headstyle } + named headwidth { headwidth } + named headlength { headlength } + right x + { + S::x & + S@T @JoinFigures + linestyle { linestyle } + linewidth { linewidth } + linecap { linecap } + dashlength { dashlength } + arrow { arrow } + headstyle { headstyle } + headwidth { headwidth } + headlength { headlength } + T + } + + macro @FirstSub { fixroot //vmargin |0.5rt firstsub } + + def @NextSub + precedence 90 + associativity left + left others + named hmargin { hmargin } + named linestyle { linestyle } + named linewidth { linewidth } + named linecap { linecap } + named dashlength { dashlength } + named arrow { arrow } + named headstyle { headstyle } + named headwidth { headwidth } + named headlength { headlength } + right x + { + others &hmargin S::x & + S@T @JoinFigures + linestyle { linestyle } + linewidth { linewidth } + linecap { linecap } + dashlength { dashlength } + arrow { arrow } + headstyle { headstyle } + headwidth { headwidth } + headlength { headlength } + T + } + + def @RightSub + precedence 90 + associativity left + left root + named hmargin { hmargin } + named linestyle { linestyle } + named linewidth { linewidth } + named linecap { linecap } + named dashlength { dashlength } + named arrow { arrow } + named headstyle { headstyle } + named headwidth { headwidth } + named headlength { headlength } + right x + { + root |hmargin { /vmargin {R::x} } | + R@T @JoinFigures + linestyle { linestyle } + linewidth { linewidth } + linecap { linecap } + dashlength { dashlength } + arrow { arrow } + headstyle { headstyle } + headwidth { headwidth } + headlength { headlength } + T + } + + def @StubSub + precedence 90 + associativity left + left root + named linestyle { linestyle } + named linewidth { linewidth } + named linecap { linecap } + named dashlength { dashlength } + { + root | + @Figure + shape { T@SW + T@W -- { 0.1 cm 0.7 cm } + T@E -- {-0.1 cm 0.7 cm } + T@SE + } + linestyle { linestyle } + linewidth { linewidth } + linecap { linecap } + dashlength { dashlength } + { @Null } + } + + def @Node + # named mark {} + right root + { + T:: root + # & T@W ++ { -0.2 cm 0.1 cm } @BaseOf mark + } + + @OneCol @OneRow x + +@End @Tree + + +def @ShowMarks + named linewidth { 0.015 cm } + named linestyle { dashed } + named dashlength { 0.15 cm } + named paint { lightgrey } + named marks { both } # none, horizontal, vertical, or both + right x +{ + @Fig + { @Box margin { 0c } linewidth { linewidth } paint { paint } + { @Figure + shape { + marks @Case { + { horizontal both } @Yield + { -0.3 cm ymark {xsize ymark} ++ {0.3 cm 0} } + else @Yield {} + } + marks @Case { + both @Yield [] + else @Yield {} + } + marks @Case { + { vertical both } @Yield + { xmark -0.3 cm {xmark ysize} ++ {0 0.3 cm} } + else @Yield {} + } + } + linewidth { linewidth } + linestyle { linestyle } + dashlength { dashlength } + x + } + } +} + + import @Fig + def @DagBox + named top {} + named mid {} + named base {} + { + @OneRow { + TOP:: @FBox top + // MID:: @FBox mid + // BASE:: @FBox base + } + } + + import @Fig + def @BlackDot + named diameter { 0.07c } + { + @Circle + margin { 0c } + paint { black } + { diameter @Wide diameter @High {} + } + } + + import @Fig + def @TVShape # television shape enclosing points ne, nw, se, sw + named nw {} + named ne {} + named sw {} + named se {} + named delta { 0.5 cm } + { + @Figure + shape { + { {nw @Min sw @Min ne @Min se} -- { delta 0 } } @Label BL + { {nw @Max sw @Max ne @Max se} ++ { delta 0 } } @Label TR + BL ++ { 0 BL @YDistance TR } @Label TL + BL ++ { BL @XDistance TR 0 } @Label BR + BL + BR [ BR ++ {0 delta} ] + BR ++ {delta delta} + TR ++ {delta -delta} [ TR -- {0 delta} ] + TR + TL [ TL -- {0 delta} ] + TL -- {delta delta} + BL ++ {-delta delta} [ BL ++ {0 delta} ] + BL + } + {} + } + + import @Fig + def @FunnyArrow + named from {} + named to {} + named arrow { forward } + { + @Figure + shape {from from ++ {0 from @YDistance to} to} + arrow { arrow } + {} + } + + def "->" { {Symbol Base} @Font "\256" } #174 decimal + def "=>" { {Symbol Base} @Font "\336" } #222 decimal + macro @JP { /0.5v } + + ################################################### + # # + # Lout keywords. # + # # + ################################################### + + def @@Begin { @Code "@Begin" } + def @@Break { @Code "@Break" } + def @@Case { @Code "@Case" } + def @@Database { @Code "@Database" } + def @@End { @Code "@End" } + def @@Font { @Code "@Font" } + def @@Galley { @Code "@Galley" } + def @@Graphic { @Code "@Graphic" } + def @@HExpand { @Code "@HExpand" } + def @@HScale { @Code "@HScale" } + def @@High { @Code "@High" } + def @@Include { @Code "@Include" } + def @@Key { @Code "@Key" } + def @@LClos { @Code "@LClos" } + def @@LEnv { @Code "@LEnv" } + def @@LInput { @Code "@LInput" } + def @@Moment { @Code "@Moment" } + def @@Next { @Code "@Next" } + def @@Null { @Code "@Null" } + def @@OneCol { @Code "@OneCol" } + def @@OneRow { @Code "@OneRow" } + def @@Open { @Code "@Open" } + def @@Prepend { @Code "@Prepend" } + def @@Rotate { @Code "@Rotate" } + def @@Space { @Code "@Space" } + def @@SysDatabase { @Code "@SysDatabase" } + def @@SysInclude { @Code "@SysInclude" } + def @@SysPrepend { @Code "@SysPrepend" } + def @@Tag { @Code "@Tag" } + def @@Tagged { @Code "@Tagged" } + def @@Use { @Code "@Use" } + def @@VExpand { @Code "@VExpand" } + def @@VScale { @Code "@VScale" } + def @@Yield { @Code "@Yield" } + def @@Wide { @Code "@Wide" } + + + ################################################### + # # + # Miscellaneous, mostly graphical definitions. # + # # + ################################################### + + def @Leaders + { .. @Leaders + } + + def @HLine { + @BackEnd @Case { + PostScript @Yield { + { 0 0 moveto xsize 0 lineto stroke } + @Graphic {} + } + PDF @Yield { + { 0 0 m __xsize 0 l S } + @Graphic {} + } + } + } + + def @VDashLine + right length + { + @BackEnd @Case { + PostScript @Yield { + length @High + { 0 0 moveto 0 ysize lineto [ 3 pt ] 0 setdash stroke } + @Graphic {} + } + PDF @Yield { + length @High + { [ __mul(3, __pt) ] 0 d 0 0 m 0 __ysize l stroke } + @Graphic {} + } + } + } + + def @LBox + right offset + { + @BackEnd @Case { + PostScript @Yield { + @OneCol @OneRow + { + { //0.2c + 0.6c @High 1.2c @Wide + { 0 0 moveto xsize 0 lineto + xsize ysize lineto 0 ysize lineto closepath + gsave 0.9 setgray fill grestore stroke } + @Graphic {} + } + ||offset @VDashLine 1c + } + } + PDF @Yield { + @OneCol @OneRow + { + { //0.2c + 0.6c @High 1.2c @Wide + { 0 0 m __xsize 0 l + __xsize __ysize l 0 __ysize l h + q 0.9 g f Q S } + @Graphic {} + } + ||offset @VDashLine 1c + } + } + } + } + + def @Arrow + right length + { @OneCol @OneRow + { + 30d @Rotate {0.12c @Wide @HLine} + // + length @Wide @HLine + // + "-30d" @Rotate {0.12c @Wide @HLine} + } + } + + def @DoubleArrow + right length + { @OneCol @OneRow + { + & 180d @Rotate @Arrow length + |0io @Arrow length + } + } + + def @Put + left coord + right x + { @OneCol @OneRow + { coord / | @OneCol @OneRow x + } + } + + macro @At { //0io } + + + ################################################### + # # + # Interpolated example documents. # + # # + ################################################### + + def @LittleEndRunPlace { @Galley } + def @LittleEndRun + force into { @LittleEndRunPlace&&preceding } + {} + + def @LittleTextPlace { @Galley } + def @LittleText into { @LittleTextPlace&&preceding } + right x + { x + } + + def @LittleFootPlace { @Galley } + def @LittleFootNote into { @LittleFootPlace&&following } + right x + { x + } + + def @LittlePageColumn + right x + { + 9px @Break 8p @Font + 2.8c @Wide x + } + + def @LittlePage + right x + { + @BackEnd @Case { + PostScript @Yield { + @HContract @VContract + { 0 0 moveto xsize 0 lineto xsize ysize lineto + 0 ysize lineto closepath stroke } @Graphic + { //0.3c ||0.3c + 9px @Break 8p @Font + 2.8c @Wide 3.8c @High x + ||0.3c //0.3c + } + } + PDF @Yield { + @HContract @VContract + { 0 0 m __xsize 0 l __xsize __ysize l 0 __ysize l s } @Graphic + { //0.3c ||0.3c + 9px @Break 8p @Font + 2.8c @Wide 3.8c @High x + ||0.3c //0.3c + } + } + } + } + + def @LittleFootSect + { 1c @Wide @HLine + //0.3v @LittleFootPlace ||0.5c + } + + def @LittlePageList + right @PageNum + { + @LittlePage { # |0.5rt @PageNum //0.8v + //0.3v @LittleTextPlace + //1rt @LittleFootSect + } + // + @LittlePageList @Next @PageNum + } + + def @LittleDocument + { @LittlePage + { @LittleTextPlace + //1rt @LittleFootSect + } + // @LittlePageList 2 + // @LittleEndRunPlace + } + + def @Strange + named @Format right @Val { [@Val] } + right x + { @Format x + } diff --git a/doc/design/outfile.ps b/doc/design/outfile.ps new file mode 100644 index 0000000..3f7525a --- /dev/null +++ b/doc/design/outfile.ps @@ -0,0 +1,11727 @@ +%!PS-Adobe-3.0 +%%Creator: Basser Lout Version 3.17 (September 1999) +%%CreationDate: Fri Sep 17 11:56:58 1999 +%%DocumentData: Binary +%%DocumentNeededResources: (atend) +%%DocumentMedia: Plain 595 842 0 white () +%%DocumentSuppliedResources: (atend) +%%Pages: (atend) +%%BoundingBox: 0 0 595 842 +%%EndComments + +%%BeginProlog +%%BeginResource: procset LoutStartUp +/m { 3 1 roll moveto show } bind def +/s { exch currentpoint exch pop moveto show } bind def +/k { exch neg 0 rmoveto show } bind def +/ul { gsave setlinewidth dup 3 1 roll + moveto lineto stroke grestore } bind def +/in { 1440 mul } def +/cm { 567 mul } def +/pt { 20 mul } def +/em { 120 mul } def +/sp { louts mul } def +/vs { loutv mul } def +/ft { loutf mul } def +/dg { } def + +/LoutGraphic { + /louts exch def + /loutv exch def + /loutf exch def + /ymark exch def + /xmark exch def + /ysize exch def + /xsize exch def +} def + +/LoutGr2 { gsave translate LoutGraphic gsave } def + +/LoutFont +{ findfont exch scalefont setfont +} bind def + +/LoutRecode { + { findfont dup length dict begin + {1 index /FID ne {def} {pop pop} ifelse} forall + /Encoding exch def + currentdict end definefont pop + } + stopped pop +} bind def + +/BeginEPSF { + /LoutEPSFState save def + /dict_count countdictstack def + /op_count count 1 sub def + userdict begin + /showpage { } def + 0 setgray 0 setlinecap + 1 setlinewidth 0 setlinejoin + 10 setmiterlimit [] 0 setdash newpath + /languagelevel where + { pop languagelevel + 1 ne + { false setstrokeadjust false setoverprint + } if + } if +} bind def + +/EndEPSF { + count op_count sub { pop } repeat + countdictstack dict_count sub { end } repeat + LoutEPSFState restore +} bind def +%%EndResource + +%%BeginResource encoding vec2 +/vec2 [ +/.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef +/.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef +/.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef +/.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef /.notdef +/space /exclam /quotedbl /numbersign /dollar /percent /ampersand /quoteright +/parenleft /parenright /asterisk /plus /comma /hyphen /period /slash +/zero /one /two /three /four /five /six /seven +/eight /nine /colon /semicolon /less /equal /greater /question +/at /A /B /C /D /E /F /G +/H /I /J /K /L /M /N /O +/P /Q /R /S /T /U /V /W +/X /Y /Z /bracketleft /backslash /bracketright /asciicircum /underscore +/quoteleft /a /b /c /d /e /f /g +/h /i /j /k /l /m /n /o +/p /q /r /s /t /u /v /w +/x /y /z /braceleft /bar /braceright /asciitilde /.notdef +/quotesinglbase /quotedblbase /ellipsis /OE /oe /quotedblleft /quotedblright /fi +/fl /endash /emdash /bullet /dagger /daggerdbl /florin /fraction +/dotlessi /grave /acute /circumflex /tilde /macron /breve /dotaccent +/dieresis /.notdef /ring /cedilla /.notdef /hungarumlaut /ogonek /caron +/space /exclamdown /cent /sterling /currency /yen /brokenbar /section +/dieresis /copyright /ordfeminine /guillemotleft /logicalnot /hyphen /registered /macron +/degree /plusminus /twosuperior /threesuperior /acute /mu /paragraph /periodcentered +/cedilla /onesuperior /ordmasculine /guillemotright /onequarter /onehalf /threequarters /questiondown +/Agrave /Aacute /Acircumflex /Atilde /Adieresis /Aring /AE /Ccedilla +/Egrave /Eacute /Ecircumflex /Edieresis /Igrave /Iacute /Icircumflex /Idieresis +/Eth /Ntilde /Ograve /Oacute /Ocircumflex /Otilde /Odieresis /multiply +/Oslash /Ugrave /Uacute /Ucircumflex /Udieresis /Yacute /Thorn /germandbls +/agrave /aacute /acircumflex /atilde /adieresis /aring /ae /ccedilla +/egrave /eacute /ecircumflex /edieresis /igrave /iacute /icircumflex /idieresis +/eth /ntilde /ograve /oacute /ocircumflex /otilde /odieresis /divide +/oslash /ugrave /uacute /ucircumflex /udieresis /yacute /thorn /ydieresis +] def +%%EndResource + +%%BeginResource: procset LoutTabPrependGraphic +% @PrependGraphic file /usr/staff/jeff/lout.lib/include/tabf.lpg +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +% % +% PostScript @SysPrependGraphic file for @Tab % +% % +% To assist in avoiding name clashes, the names % +% of all these symbols begin with "ltab". % +% % +% Jeffrey H. Kingston % +% 24 September 1991 % +% 22 December 1992 % +% % +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +% linewidth ltabhs - +% horizontal single line +/ltabhs +{ 0 0 moveto xsize 0 lineto + setlinewidth 0 setlinecap stroke +} def + +% linewidth ltabhsp - +% horizontal single line with projecting ends +/ltabhsp +{ 0 0 moveto xsize 0 lineto + setlinewidth 2 setlinecap stroke +} def + +% linewidth ltabhd - +% horizontal double line +/ltabhd +{ dup dup + 0 0 moveto xsize 0 lineto + 0 exch 3 mul moveto xsize exch 3 mul lineto + setlinewidth 0 setlinecap stroke +} def + +% linewidth ltabhdb - +% horizontal double line below mark +/ltabhdb +{ dup dup + 0 0 moveto xsize 0 lineto + 0 exch -3 mul moveto xsize exch -3 mul lineto + setlinewidth 0 setlinecap stroke +} def + +% linewidth ltabhdnw - +% horizontal double line with northwest corner +/ltabhdnw +{ dup dup dup dup + 0 0 moveto xsize 0 lineto + xsize exch 3 mul moveto + -3 mul exch 3 mul lineto + -3 mul 0 lineto + setlinewidth 0 setlinejoin 2 setlinecap stroke +} def + +% linewidth ltabhdne - +% horizontal double line with northeast corner +/ltabhdne +{ dup dup dup dup + 0 0 moveto xsize 0 lineto + 0 exch 3 mul moveto + 3 mul xsize add exch 3 mul lineto + 3 mul xsize add 0 lineto + setlinewidth 0 setlinejoin 2 setlinecap stroke +} def + +% linewidth ltabhdsw - +% horizontal double line with southwest corner +/ltabhdsw +{ dup dup dup dup + 0 0 moveto xsize 0 lineto + xsize exch -3 mul moveto + -3 mul exch -3 mul lineto + -3 mul 0 lineto + setlinewidth 0 setlinejoin 2 setlinecap stroke +} def + +% linewidth ltabhdse - +% horizontal double line with southeast corner +/ltabhdse +{ dup dup dup dup + 0 0 moveto xsize 0 lineto + 0 exch -3 mul moveto + 3 mul xsize add exch -3 mul lineto + 3 mul xsize add 0 lineto + setlinewidth 0 setlinejoin 2 setlinecap stroke +} def + +% linewidth ltabvs - +% vertical single line +/ltabvs +{ 0 0 moveto 0 ysize lineto + setlinewidth 0 setlinecap stroke +} def + +% linewidth ltabvd - +% vertical double line +/ltabvd +{ dup dup + 0 0 moveto 0 ysize lineto + -3 mul 0 moveto -3 mul ysize lineto + setlinewidth 0 setlinecap stroke +} def + +% linewidth ltabvdr - +% vertical double line to right of mark +/ltabvdr +{ dup dup + 0 0 moveto 0 ysize lineto + 3 mul 0 moveto 3 mul ysize lineto + setlinewidth 0 setlinecap stroke +} def +%%EndResource + +%%BeginResource: procset LoutFigPrependGraphic +% @PrependGraphic file /usr/staff/jeff/lout.lib/include/figf.lpg +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% +% % +% PostScript @SysPrependGraphic file for @Fig Jeffrey H. Kingston % +% Version 2.0 (includes CIRCUM label) January 1992 % +% % +% To assist in avoiding name clashes, the names of all symbols % +% defined here begin with "lfig". However, this is not feasible % +% with user-defined labels and some labels used by users. % +% % +% <point> is two numbers, a point. % +% <length> is one number, a length % +% <angle> is one number, an angle in degrees % +% <dashlength> is one number, the preferred length of a dash % +% % +%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% + +errordict begin + /handleerror + { + { /Times-Roman findfont 8 pt scalefont setfont + 0 setgray 4 pt 4 pt moveto + $error /errorname get + dup lfigdict exch known + { lfigdict exch get } + { 30 string cvs } ifelse + show + ( Command: ) show + $error /command get 30 string cvs show + } stopped {} if + showpage stop + } def +end + +% concat strings: <string> <string> lfigconcat <string> +% must be defined outside lfigdict since used in lfigpromotelabels +/lfigconcat +{ 2 copy length exch length add string + dup 0 4 index putinterval + dup 3 index length 3 index putinterval + 3 1 roll pop pop +} def + +% <string> lfigdebugprint - +% must be defined outside lfigdict since used in arbitrary places +% /lfigdebugprint +% { print +% (; operand stack:\n) print +% count copy +% count 2 idiv +% { == +% (\n) print +% } repeat +% (\n) print +% } def + +/lfigdict 120 dict def +lfigdict begin + +% error messages +/dictfull (dictfull error: too many labels?) def +/dictstackoverflow (dictstackoverflow error: labels nested too deeply?) def +/execstackoverflow (execstackoverflow error: figure nested too deeply?) def +/limitcheck (limitcheck error: figure nested too deeply or too large?) def +/syntaxerror (syntaxerror error: syntax error in text of figure?) def +/typecheck (typecheck error: syntax error in text of figure?) def +/undefined (undefined error: unknown or misspelt label?) def +/VMError (VMError error: run out of memory?) def + +% push pi onto stack: - lfigpi <num> +/lfigpi 3.14159 def + +% arc directions +/clockwise false def +/anticlockwise true def + +% maximum of two numbers: <num> <num> lfigmax <num> +/lfigmax { 2 copy gt { pop } { exch pop } ifelse } def + +% minimum of two numbers: <num> <num> lfigmin <num> +/lfigmin { 2 copy lt { pop } { exch pop } ifelse } def + +% add two points: <point> <point> lfigpadd <point> +/lfigpadd { exch 3 1 roll add 3 1 roll add exch } def + +% subtract first point from second: <point> <point> lfigpsub <point> +/lfigpsub { 3 2 roll sub 3 1 roll exch sub exch } def + +% max two points: <point> <point> lfigpmax <point> +/lfigpmax { exch 3 1 roll lfigmax 3 1 roll lfigmax exch } def + +% min two points: <point> <point> lfigpmin <point> +/lfigpmin { exch 3 1 roll lfigmin 3 1 roll lfigmin exch } def + +% scalar multiplication: <point> <num> lfigpmul <point> +/lfigpmul { dup 3 1 roll mul 3 1 roll mul exch } def + +% point at angle and distance: <point> <length> <angle> lfigatangle <point> +/lfigatangle { 2 copy cos mul 3 1 roll sin mul lfigpadd } def + +% angle from one point to another: <point> <point> lfigangle <angle> +/lfigangle { lfigpsub 2 copy 0 eq exch 0 eq and {pop} {exch atan} ifelse } def + +% distance between two points: <point> <point> lfigdistance <length> +/lfigdistance { lfigpsub dup mul exch dup mul add sqrt } def + +% difference in x coords: <point> <point> lfigxdistance <length> +/lfigxdistance { pop 3 1 roll pop sub } def + +%difference in y coords: <point> <point> lfigydistance <length> +/lfigydistance { 3 1 roll pop sub exch pop } def + +% stroke a solid line: <length> <dashlength> lfigsolid - +/lfigsolid +{ pop pop [] 0 setdash stroke +} def + +% stroke a lfigdashed line: <length> <dashlength> lfigdashed - +/lfigdashed +{ 2 copy div 2 le 1 index 0 le or + { exch pop 1 pt lfigmax [ exch dup ] 0 setdash } + { dup [ exch 4 2 roll 2 copy div + 1 sub 2 div ceiling dup 4 1 roll + 1 add mul sub exch div ] 0 setdash + } ifelse stroke +} def + +% stroke a lfigcdashed line: <length> <dashlength> lfigcdashed - +/lfigcdashed +{ 2 copy le 1 index 0 le or + { exch pop 1 pt lfigmax [ exch dup ] dup 0 get 2 div setdash } + { dup [ 4 2 roll exch 2 copy exch div + 2 div ceiling div 1 index sub + ] exch 2 div setdash + } ifelse stroke +} def + +% stroke a dotted line: <length> <dashlength> lfigdotted - +/lfigdotted +{ 2 copy le 1 index 0 le or + { exch pop 1 pt lfigmax [ exch 0 exch ] 0 setdash } + { 1 index exch div ceiling div + [ 0 3 2 roll ] 0 setdash + } ifelse stroke +} def + +% stroke a noline line: <length> <dashlength> lfignoline - +/lfignoline +{ pop pop +} def + +% painting (i.e. filling): - lfigwhite - (etc.) +/lfignopaint { } def +/lfignochange { fill } def +/lfigdarkblue { 0.0 0.0 0.5 setrgbcolor fill } def +/lfigblue { 0.0 0.0 1.0 setrgbcolor fill } def +/lfiglightblue { 0.5 0.5 1.0 setrgbcolor fill } def +/lfigdarkgreen { 0.0 0.5 0.0 setrgbcolor fill } def +/lfiggreen { 0.0 1.0 0.0 setrgbcolor fill } def +/lfiglightgreen { 0.5 1.0 0.5 setrgbcolor fill } def +/lfigdarkred { 0.5 0.0 0.0 setrgbcolor fill } def +/lfigred { 1.0 0.0 0.0 setrgbcolor fill } def +/lfiglightred { 1.0 0.5 0.5 setrgbcolor fill } def +/lfigdarkcyan { 0.0 0.5 0.5 setrgbcolor fill } def +/lfigcyan { 0.0 1.0 1.0 setrgbcolor fill } def +/lfiglightcyan { 0.5 1.0 1.0 setrgbcolor fill } def +/lfigdarkmagenta { 0.5 0.0 0.5 setrgbcolor fill } def +/lfigmagenta { 1.0 0.0 1.0 setrgbcolor fill } def +/lfiglightmagenta { 1.0 0.5 1.0 setrgbcolor fill } def +/lfigdarkyellow { 0.5 0.5 0.0 setrgbcolor fill } def +/lfigyellow { 1.0 1.0 0.0 setrgbcolor fill } def +/lfiglightyellow { 1.0 1.0 0.5 setrgbcolor fill } def +/lfigdarkgray { 0.2 0.2 0.2 setrgbcolor fill } def +/lfiggray { 0.5 0.5 0.5 setrgbcolor fill } def +/lfiglightgray { 0.8 0.8 0.8 setrgbcolor fill } def +/lfigdarkgrey { 0.2 0.2 0.2 setrgbcolor fill } def +/lfiggrey { 0.5 0.5 0.5 setrgbcolor fill } def +/lfiglightgrey { 0.8 0.8 0.8 setrgbcolor fill } def +/lfigblack { 0.0 0.0 0.0 setrgbcolor fill } def +/lfigwhite { 1.0 1.0 1.0 setrgbcolor fill } def + +% line caps (and joins, not currently used) +/lfigbutt 0 def +/lfiground 1 def +/lfigprojecting 2 def +/lfigmiter 0 def +/lfigbevel 2 def + +% shape and labels of the @Box symbol +/lfigbox +{ + 0 0 /SW lfigpointdef + xsize 0 /SE lfigpointdef + xsize ysize /NE lfigpointdef + 0 ysize /NW lfigpointdef + SE 0.5 lfigpmul /S lfigpointdef + NW 0.5 lfigpmul /W lfigpointdef + W SE lfigpadd /E lfigpointdef + S NW lfigpadd /N lfigpointdef + NE 0.5 lfigpmul /CTR lfigpointdef + [ CTR NE lfigpsub /lfigboxcircum cvx ] lfigcircumdef + SW SE NE NW SW +} def + +% shape and labels of the @CurveBox symbol +/lfigcurvebox +{ + + xsize 0.5 mul ysize 0.5 mul /CTR lfigpointdef + xsize 0.5 mul 0 /S lfigpointdef + xsize ysize 0.5 mul /E lfigpointdef + xsize 0.5 mul ysize /N lfigpointdef + 0 ysize 0.5 mul /W lfigpointdef + + xmark 0.293 mul xmark 0.293 mul /SW lfigpointdef + xsize xmark 0.293 mul sub xmark 0.293 mul /SE lfigpointdef + xsize xmark 0.293 mul sub ysize xmark 0.293 mul sub /NE lfigpointdef + xmark 0.293 mul ysize xmark 0.293 mul sub /NW lfigpointdef + + [ xsize ysize 0.5 lfigpmul xmark /lfigcurveboxcircum cvx ] lfigcircumdef + + xmark 0 + xsize xmark sub 0 + [ xsize xmark sub xmark ] + xsize xmark + xsize ysize xmark sub + [ xsize xmark sub ysize xmark sub ] + xsize xmark sub ysize + xmark ysize + [ xmark ysize xmark sub ] + 0 ysize xmark sub + 0 xmark + [ xmark xmark ] + xmark 0 +} def + +% shadow of the @ShadowBox symbol +% its shape and labels are done, somewhat inaccurately, with lfigbox +/lfigshadow +{ xmark 2 mul 0 moveto xsize 0 lineto + xsize ysize xmark 2 mul sub lineto + xsize xmark sub ysize xmark 2 mul sub lineto + xsize xmark sub xmark lineto + xmark 2 mul xmark lineto closepath fill +} def + +% shape and labels of the @Square symbol +/lfigsquare +{ + xsize ysize 0.5 lfigpmul /CTR lfigpointdef + CTR xsize xsize ysize ysize lfigpmax 0.5 lfigpmul lfigpadd /NE lfigpointdef + CTR 0 0 CTR NE lfigdistance 135 lfigatangle lfigpadd /NW lfigpointdef + CTR 0 0 CTR NE lfigdistance 225 lfigatangle lfigpadd /SW lfigpointdef + CTR 0 0 CTR NE lfigdistance 315 lfigatangle lfigpadd /SE lfigpointdef + SW 0.5 lfigpmul SE 0.5 lfigpmul lfigpadd /S lfigpointdef + NW 0.5 lfigpmul NE 0.5 lfigpmul lfigpadd /N lfigpointdef + SW 0.5 lfigpmul NW 0.5 lfigpmul lfigpadd /W lfigpointdef + SE 0.5 lfigpmul NE 0.5 lfigpmul lfigpadd /E lfigpointdef + [ CTR NE lfigpsub /lfigboxcircum cvx ] lfigcircumdef + SW SE NE NW SW +} def + +% shape and labels of the @Diamond symbol +/lfigdiamond +{ + xsize 0 0.5 lfigpmul /S lfigpointdef + 0 ysize 0.5 lfigpmul /W lfigpointdef + S W lfigpadd /CTR lfigpointdef + CTR W lfigpadd /N lfigpointdef + CTR S lfigpadd /E lfigpointdef + [ xsize ysize 0.5 lfigpmul /lfigdiamondcircum cvx ] lfigcircumdef + S E N W S +} def + +% shape and labels of the @Ellipse symbol +/lfigellipse +{ + xsize 0 0.5 lfigpmul /S lfigpointdef + 0 ysize 0.5 lfigpmul /W lfigpointdef + S W lfigpadd /CTR lfigpointdef + CTR W lfigpadd /N lfigpointdef + CTR S lfigpadd /E lfigpointdef + CTR xsize 0 0.3536 lfigpmul lfigpadd 0 ysize 0.3536 lfigpmul lfigpadd /NE lfigpointdef + 0 ysize 0.3536 lfigpmul CTR xsize 0 0.3536 lfigpmul lfigpadd lfigpsub /SE lfigpointdef + xsize 0 0.3536 lfigpmul CTR lfigpsub 0 ysize 0.3536 lfigpmul lfigpadd /NW lfigpointdef + 0 ysize 0.3536 lfigpmul xsize 0 0.3536 lfigpmul CTR lfigpsub lfigpsub /SW lfigpointdef + [ xsize ysize 0.5 lfigpmul /lfigellipsecircum cvx ] lfigcircumdef + S [ CTR ] E [ CTR ] N [ CTR ] W [ CTR ] S +} def + +% shape and labels of the @Circle symbol +/lfigcircle +{ + xsize ysize 0.5 lfigpmul /CTR lfigpointdef + CTR xsize 0 ysize 0 lfigpmax 0.5 lfigpmul lfigpadd /E lfigpointdef + CTR 0 0 CTR E lfigdistance 45 lfigatangle lfigpadd /NE lfigpointdef + CTR 0 0 CTR E lfigdistance 90 lfigatangle lfigpadd /N lfigpointdef + CTR 0 0 CTR E lfigdistance 135 lfigatangle lfigpadd /NW lfigpointdef + CTR 0 0 CTR E lfigdistance 180 lfigatangle lfigpadd /W lfigpointdef + CTR 0 0 CTR E lfigdistance 225 lfigatangle lfigpadd /SW lfigpointdef + CTR 0 0 CTR E lfigdistance 270 lfigatangle lfigpadd /S lfigpointdef + CTR 0 0 CTR E lfigdistance 315 lfigatangle lfigpadd /SE lfigpointdef + [ S E lfigpsub /lfigellipsecircum cvx ] lfigcircumdef + S [ CTR ] E [ CTR ] N [ CTR ] W [ CTR ] S +} def + +% shape and labels of the @HLine and @HArrow symbols +/lfighline +{ + 0 ymark lfigprevious /FROM lfigpointdef + xsize ymark lfigprevious /TO lfigpointdef +} def + +% shape and labels of the @VLine and @VArrow symbols +/lfigvline +{ + xmark ysize lfigprevious /FROM lfigpointdef + xmark 0 lfigprevious /TO lfigpointdef +} def + +% points of a polygon around base with given no of sides, vert init angle: +% <sides> <angle> figpolygon <point> ... <point> +/lfigpolygon +{ xsize ysize 0.5 lfigpmul /CTR lfigpointdef + 90 sub CTR 2 copy lfigmax 5 3 roll + [ 4 copy pop /lfigpolycircum cvx ] lfigcircumdef + exch dup 360 exch div exch + 1 1 3 2 roll + { 4 string cvs (P) exch lfigconcat cvn + 6 copy pop pop lfigatangle 2 copy 10 2 roll + 3 2 roll lfigpointdef + dup 3 1 roll add exch + } for + pop lfigatangle +} def + +% next array element: <array> <index> lfiggetnext <array> <index> <any> true +% or <array> <index> false +/lfiggetnext +{ 2 copy exch length ge + { false } + { 2 copy get exch 1 add exch true } ifelse +} def + +% check whether thing is number: <any> lfigisnumbertype <any> <bool> +/lfigisnumbertype +{ dup type dup + /integertype eq exch /realtype eq or +} def + +% check whether thing is an array: <any> lfigisarraytype <any> <bool> +/lfigisarraytype { dup type /arraytype eq } def + +% get next item: <array> <index> lfiggetnextitem <array> <index> 0 +% or <array> <index> <array> 1 +% or <array> <index> <point> 2 +/lfiggetnextitem +{ lfiggetnext + { lfigisarraytype + { 1 + } + { lfigisnumbertype + { 3 1 roll + lfiggetnext + { lfigisnumbertype + { 4 3 roll exch 2 + } + { pop 3 2 roll pop 0 + } ifelse + } + { 3 2 roll pop 0 + } ifelse + } + { pop 0 + } ifelse + } ifelse + } + { 0 + } ifelse +} def + +% set arc path: bool x1 y1 x2 y2 x0 y0 lfigsetarc <angle> <angle> <dist> +% the path goes from x1 y1 to x2 y2 about centre x0 y0, +% anticlockwise if bool is true else clockwise. +% The orientations of backwards pointing and forwards pointing +% arrowheads are returned in the two angles, and +% the length of the arc is returned in <dist>. +/lfigsetarc +{ + 20 dict begin + matrix currentmatrix 8 1 roll + 2 copy translate 2 copy 8 2 roll + 4 2 roll lfigpsub 6 2 roll lfigpsub + dup /y1 exch def dup mul /y1s exch def + dup /x1 exch def dup mul /x1s exch def + dup /y2 exch def dup mul /y2s exch def + dup /x2 exch def dup mul /x2s exch def + + y1s y2s eq + { -1 + } + { y1s x2s mul y2s x1s mul sub y1s y2s sub div + } ifelse + /da exch def + + x1s x2s eq + { -1 + } + { x1s y2s mul x2s y1s mul sub x1s x2s sub div + } ifelse + /db exch def + + da 0 gt db 0 gt and + { /LMax da sqrt db sqrt lfigmax def + /scalex da sqrt LMax div def + /scaley db sqrt LMax div def + scalex scaley scale + 0 0 LMax + 0 0 x1 scalex mul y1 scaley mul lfigangle + 0 0 x2 scalex mul y2 scaley mul lfigangle + 2 copy eq { 360 add } if + 2 copy 8 2 roll + 5 index { arc } { arcn } ifelse + 2 index 1 index + { 90 sub } { 90 add } ifelse + dup sin scaley mul exch cos scalex mul atan + 2 index 2 index + { 90 add } { 90 sub } ifelse + dup sin scaley mul exch cos scalex mul atan + 5 2 roll % res1 res2 ang1 ang2 anticlockwise + { exch sub } { sub } ifelse + dup 0 le { 360 add } if lfigpi mul LMax mul 180 div + } + { 0 0 x1 y1 lfigdistance 0 0 x2 y2 lfigdistance eq + 0 0 x1 y1 lfigdistance 0 gt and + { 0 0 + 0 0 x1 y1 lfigdistance + 0 0 x1 y1 lfigangle + 0 0 x2 y2 lfigangle + 2 copy eq { 360 add } if + 2 copy 8 2 roll + 5 index { arc } { arcn } ifelse + 2 index 1 index + { 90 sub } { 90 add } ifelse + 2 index 2 index + { 90 add } { 90 sub } ifelse + 5 2 roll % res1 res2 ang1 ang2 clockwise + { exch sub } { sub } ifelse + dup 0 le { 360 add } if lfigpi mul 0 0 x1 y1 lfigdistance mul 180 div + } + { x2 y2 lineto pop + x2 y2 x1 y1 lfigangle + x1 y1 x2 y2 lfigangle + x1 y1 x2 y2 lfigdistance + } ifelse + } ifelse + 4 -1 roll setmatrix + end +} def + +% lfigsetcurve: set up a Bezier curve from x0 y0 to x3 y3 +% and return arrowhead angles and length of curve (actually 0) +% x0 y0 x1 y1 x2 y2 x3 y3 lfigsetcurve <angle> <angle> <length> +/lfigsetcurve +{ 8 copy curveto pop pop + lfigangle + 5 1 roll + 4 2 roll lfigangle + exch + 0 +} def + +% lfigpaintpath: paint a path of the given shape +% /paint [ shape ] lfigpaintpath - +/lfigpaintpath +{ + 10 dict begin + 0 newpath + /prevseen false def + /curveseen false def + { lfiggetnextitem + dup 0 eq { pop exit } + { 1 eq + { /curveseen true def + /curve exch def + curve length 0 eq { /curveseen false def } if + } + { /ycurr exch def + /xcurr exch def + prevseen + { curveseen + { curve length 4 eq + { xprev yprev + curve 0 get curve 1 get + curve 2 get curve 3 get + xcurr ycurr + lfigsetcurve pop pop pop + } + { xprev yprev xcurr ycurr + curve length 1 ge { curve 0 get } { 0 } ifelse + curve length 2 ge { curve 1 get } { 0 } ifelse + curve length 3 ge { curve 2 get } { true } ifelse + 7 1 roll + lfigsetarc pop pop pop + } ifelse + } + { xcurr ycurr lineto + } ifelse + } + { xcurr ycurr moveto + } ifelse + /xprev xcurr def + /yprev ycurr def + /prevseen true def + /curveseen false def + } ifelse + } ifelse + } loop pop pop cvx exec + end +} def + +% stroke a path of the given shape in the given linestyle and dash length. +% Return the origin and angle of the backward and forward arrow heads. +% dashlength /linestyle [shape] lfigdopath [<point> <angle>] [<point> <angle>] +/lfigdopath +{ + 10 dict begin + 0 + /prevseen false def + /curveseen false def + /backarrow [] def + /fwdarrow [] def + { + lfiggetnextitem + dup 0 eq { pop exit } + { + 1 eq + { /curveseen true def + /curve exch def + curve length 0 eq { /prevseen false def } if + } + { /ycurr exch def + /xcurr exch def + prevseen + { newpath xprev yprev moveto + curveseen + { curve length 4 eq + { xprev yprev + curve 0 get curve 1 get + curve 2 get curve 3 get + xcurr ycurr lfigsetcurve + } + { xprev yprev xcurr ycurr + curve length 1 ge { curve 0 get } { 0 } ifelse + curve length 2 ge { curve 1 get } { 0 } ifelse + curve length 3 ge { curve 2 get } { true } ifelse + 7 1 roll + lfigsetarc + } ifelse + } + { xcurr ycurr lineto + xcurr ycurr xprev yprev lfigangle dup 180 sub + xprev yprev xcurr ycurr lfigdistance + } ifelse + 6 index 6 index cvx exec + [ xprev yprev 5 -1 roll ] + backarrow length 0 eq + { /backarrow exch def } + { pop } ifelse + [ xcurr ycurr 4 -1 roll ] /fwdarrow exch def + } if + /xprev xcurr def + /yprev ycurr def + /prevseen true def + /curveseen false def + } ifelse + } ifelse + } loop + pop pop pop pop + backarrow length 0 eq { [ 0 0 0 ] } { backarrow } ifelse + fwdarrow length 0 eq { [ 0 0 0 ] } { fwdarrow } ifelse + end +} def + +% lfigdoarrow: draw an arrow head of given form +% dashlength /lstyle /pstyle hfrac height width [ <point> <angle> ] lfigdoarrow - +/lfigdoarrow +{ matrix currentmatrix 8 1 roll + dup 0 get 1 index 1 get translate + 2 get rotate + [ 2 index neg 2 index 0 0 + 3 index 3 index neg + 1 index 10 index mul 0 + 7 index 7 index ] + 4 1 roll pop pop pop + dup 3 1 roll + gsave lfigpaintpath grestore lfigdopath pop pop + setmatrix +} def + +% arrow head styles +/lfigopen 0.0 def +/lfighalfopen 0.5 def +/lfigclosed 1.0 def + +% stroke no arrows, forward, back, and both +/lfignoarrow { pop pop pop pop pop pop pop pop } def +/lfigforward { 7 -1 roll lfigdoarrow pop } def +/lfigback { 8 -2 roll pop lfigdoarrow } def +/lfigboth { 8 -1 roll 7 copy lfigdoarrow pop 7 -1 roll lfigdoarrow } def + +% lfigprevious: return previous point on path +/lfigprevious +{ lfigisnumbertype + { 2 copy } + { lfigisarraytype + { 2 index 2 index } + { 0 0 } + ifelse + } ifelse +} def + +% label a point in 2nd top dictionary: <point> /name lfigpointdef - +/lfigpointdef +{ + % (Entering lfigpointdef) lfigdebugprint + [ 4 2 roll transform + /itransform cvx ] cvx + currentdict end + 3 1 roll + % currentdict length currentdict maxlength lt + % { def } + % { exec moveto (too many labels) show stop } + % ifelse + def + begin + % (Leaving lfigpointdef) lfigdebugprint +} def + +% promote labels from second top to third top dictionary +% <string> lfigpromotelabels - +/lfigpromotelabels +{ + % (Entering lfigpromotelabels) lfigdebugprint + currentdict end exch currentdict end + { exch 20 string cvs 2 index + (@) lfigconcat exch lfigconcat cvn exch def + } forall pop begin + % (Leaving lfigpromotelabels) lfigdebugprint +} def + +% show labels (except CIRCUM): - lfigshowlabels - +/lfigshowlabels +{ + % (Entering lfigshowlabels) lfigdebugprint + currentdict end + currentdict + { 1 index 20 string cvs (CIRCUM) search % if CIRCUM in key + { pop pop pop pop pop } + { pop cvx exec 2 copy + newpath 1.5 pt 0 360 arc + 0 setgray fill + /Times-Roman findfont 8 pt scalefont setfont + moveto 0.2 cm 0.1 cm rmoveto 20 string cvs show + } + ifelse + } forall + begin + % (Leaving lfigshowlabels) lfigdebugprint +} def + +% fix an angle to 0 <= res < 360: <angle> lfigfixangle <angle> +/lfigfixangle +{ + % (Entering lfigfixangle) lfigdebugprint + { dup 0 ge { exit } if + 360 add + } loop + { dup 360 lt { exit } if + 360 sub + } loop + % (Leaving lfigfixangle) lfigdebugprint +} def + +% find point on circumference of box: alpha a b lfigboxcircum x y +/lfigboxcircum +{ + % (Entering lfigboxcircum) lfigdebugprint + 4 dict begin + /b exch def + /a exch def + lfigfixangle /alpha exch def + 0 0 a b lfigangle /theta exch def + + % if alpha <= theta, return (a, a*tan(alpha)) + alpha theta le + { a a alpha sin mul alpha cos div } + { + % else if alpha <= 180 - theta, return (b*cot(alpha), b) + alpha 180 theta sub le + { b alpha cos mul alpha sin div b } + { + % else if alpha <= 180 + theta, return (-a, -a*tan(alpha)) + alpha 180 theta add le + { a neg a neg alpha sin mul alpha cos div } + { + % else if alpha <= 360 - theta, return (-b*cot(alpha), -b) + alpha 360 theta sub le + { b neg alpha cos mul alpha sin div b neg } + { + % else 360 - theta <= alpha, return (a, a*tan(alpha)) + a a alpha sin mul alpha cos div + } ifelse + } ifelse + } ifelse + } ifelse + end + % (Leaving lfigboxcircum) lfigdebugprint +} def + +% find quadratic roots (assume a != 0): a b c lfigqroots x1 x2 2 +% or x2 1 +% or 0 +/lfigqroots +{ + 4 dict begin + /c exch def + /b exch def + /a exch def + /disc b b mul 4 a c mul mul sub def + disc 0 lt + { 0 + } + { disc 0 eq + { b neg 2 a mul div + 1 + } + { b neg disc sqrt add 2 a mul div + b neg disc sqrt sub 2 a mul div + 2 + } + ifelse + } + ifelse + end +} def + +% work our which quadrant: <angle> lfigquadrant <0-3> +/lfigquadrant +{ dup 90 lt + { pop 0 + } + { dup 180 lt + { pop 1 + } + { 270 lt + { 2 + } + { 3 + } ifelse + } ifelse + } ifelse +} def + +% find curvebox circum, assuming upper right quadrant: alpha a b xmk lfigcb x y +/lfigcb +{ + 6 dict begin + /xmk exch def + /b exch def + /a exch def + /alpha exch def + /theta1 0 0 a b xmk sub lfigangle def + /theta2 0 0 a xmk sub b lfigangle def + alpha theta1 le + { % if alpha <= theta1, return (a, a*tan(alpha)) + a a alpha sin mul alpha cos div + } + { alpha theta2 ge + { % else if alpha > theta2, return (b*cot(alpha), b) + b alpha cos mul alpha sin div b + } + { + % else, return the intersection of line and circle + a xmk sub b xmk sub xmk 0 0 alpha lfigcircleintersect + dup 0 eq + { % should never happen, just return any reasonable point + pop + a b 0.5 lfigpmul + } + { 1 eq + { % should never happen, just return the point on top of stack + } + { % the usual case, two points on stack, return the larger + lfigpmax + } ifelse + } ifelse + } ifelse + } ifelse + end +} def + +% find point on circumference of curvebox: alpha a b xmk lfigcurveboxcircum x y +/lfigcurveboxcircum +{ + % (Entering lfigcurveboxcircum) lfigdebugprint + 5 dict begin + /xmk exch def + /b exch def + /a exch def + lfigfixangle /alpha exch def + + % work out which quadrant we are in, and reflect accordingly + /quad alpha lfigquadrant def + quad 0 eq + { alpha a b xmk lfigcb + } + { quad 1 eq + { 180 alpha sub a b xmk lfigcb exch neg exch + } + { quad 2 eq + { alpha 180 sub a b xmk lfigcb neg exch neg exch + } + { 360 alpha sub a b xmk lfigcb neg + } ifelse + } ifelse + } ifelse + end + % (Leaving lfigcurveboxcircum) lfigdebugprint +} def + +% find point on circumference of diamond: alpha a b lfigdiamondcircum x y +/lfigdiamondcircum +{ + % (Entering lfigdiamondcircum) lfigdebugprint + 4 dict begin + /b exch def + /a exch def + lfigfixangle /alpha exch def + b alpha cos abs mul a alpha sin abs mul add /denom exch def + a b mul alpha cos mul denom div + a b mul alpha sin mul denom div + end + % (Leaving lfigdiamondcircum) lfigdebugprint +} def + +% find point on circumference of ellipse: alpha a b lfigellipsecircum x y +/lfigellipsecircum +{ + % (Entering lfigellipsecircum) lfigdebugprint + 4 dict begin + /b exch def + /a exch def + lfigfixangle /alpha exch def + b alpha cos mul dup mul a alpha sin mul dup mul add sqrt /denom exch def + a b mul alpha cos mul denom div + a b mul alpha sin mul denom div + end + % (Leaving lfigellipsecircum) lfigdebugprint +} def + +% find point of intersection of two lines each defined by two points +% x1 y1 x2 y2 x3 y3 x4 y4 lfiglineintersect x y +/lfiglineintersect +{ + % (Entering lfiglineintersect) lfigdebugprint + 13 dict begin + /y4 exch def + /x4 exch def + /y3 exch def + /x3 exch def + /y2 exch def + /x2 exch def + /y1 exch def + /x1 exch def + x2 x1 sub /x21 exch def + x4 x3 sub /x43 exch def + y2 y1 sub /y21 exch def + y4 y3 sub /y43 exch def + y21 x43 mul y43 x21 mul sub /det exch def + + % calculate x + y21 x43 mul x1 mul + y43 x21 mul x3 mul sub + y3 y1 sub x21 mul x43 mul add + det div + + % calculate y + x21 y43 mul y1 mul + x43 y21 mul y3 mul sub + x3 x1 sub y21 mul y43 mul add + det neg div + + end + % (Leaving lfiglineintersect) lfigdebugprint +} def + +% find point on circumference of polygon +% alpha radius num theta lfigpolycircum x y +/lfigpolycircum +{ + % (Entering lfigpolycircum) lfigdebugprint + 13 dict begin + /theta exch def + /num exch def + /radius exch def + /alpha exch def + + % calculate delta, the angle from theta to alpha + alpha theta sub lfigfixangle + + % calculate the angle which is the multiple of 360/num closest to delta + 360 num div div truncate 360 num div mul theta add /anglea exch def + + % calculate the next multiple of 360/num after anglea + anglea 360 num div add /angleb exch def + + % intersect the line through these two points with the alpha line + anglea cos anglea sin angleb cos angleb sin + 0 0 alpha cos 2 mul alpha sin 2 mul + lfiglineintersect radius lfigpmul + + end + % (Leaving lfigpolycircum) lfigdebugprint +} def + +% find point of intersection of a point and a circle +% x0 y0 r x1 y1 theta lfigcircleintersect xa ya xb yb 2 +% or xb yb 1 +% or 0 +/lfigcircleintersect +{ + % (Entering lfigcircleintersect) lfigdebugprint + 15 dict begin + /theta exch def + /y1 exch def + /x1 exch def + /r exch def + /y0 exch def + /x0 exch def + + % if sin(theta) = 0 then line is horizontal and y must be y1 + theta sin abs 0.00001 lt + { + /a 1 def + /b -2 x0 mul def + /c x0 dup mul y1 y0 sub dup mul add r dup mul sub def + a b c lfigqroots dup + 0 eq + { pop + 0 + } + { 1 eq + { y1 1 + } + { y1 exch y1 2 + } ifelse + } ifelse + } + { + /ct theta cos theta sin div def + /a ct ct mul 1 add def + /b ct x1 x0 sub mul y1 add y0 sub 2 mul def + /c x1 x0 sub dup mul y1 y0 sub dup mul add r dup mul sub def + a b c lfigqroots dup + 0 eq + { pop + 0 + } + { 1 eq + { y1 add /yb exch def + yb y1 sub ct mul x1 add /xb exch def + xb yb 1 + } + { y1 add /ya exch def + ya y1 sub ct mul x1 add /xa exch def + y1 add /yb exch def + yb y1 sub ct mul x1 add /xb exch def + xa ya xb yb 2 + } ifelse + } ifelse + } ifelse + end + % (Leaving lfigcircleintersect) lfigdebugprint +} def + +% add CIRCUM operator with this body: <array> lfigcircumdef - +/lfigcircumdef +{ % (Entering lfigcircumdef) lfigdebugprint + /CIRCUM exch cvx + currentdict end + 3 1 roll + % currentdict length currentdict maxlength lt + % { def } + % { exec moveto (too many labels) show stop } + % ifelse + def + begin + % (Leaving lfigcircumdef) lfigdebugprint +} def + +end +%%EndResource + +%%BeginResource: procset LoutBasicSetup +% @PrependGraphic file /usr/staff/jeff/lout.lib/include/bsf.lpg + +% width height linethickness louteuro - +% draw a Euro symbol of this width and height with this line thickness +% Author: Jeff Kingston, based on code from Andrew Beardsley +/louteuro { + 20 dict begin + /eurothick exch def + /euroheight exch def + /eurowidth exch def + /eurostrokewidth euroheight 0.8 mul def + /eurostep eurothick 60 cos mul 60 sin div def + /eurotheta 40 def + + % llx lly width thickness louteurobox - + % draw angled box starting at (llx, lly) with given width and thickness + /louteurobox + { + /euroboxthick exch def + /euroboxwidth exch def + newpath moveto euroboxwidth 0 rlineto + eurostep euroboxthick rlineto + euroboxwidth neg 0 rlineto closepath fill + } def + + % lower cross stroke + 0 euroheight 2 div eurothick 1.5 mul sub + eurostrokewidth eurothick louteurobox + + % upper cross stroke + 0 euroheight 2 div eurothick 0.5 mul add + eurostrokewidth eurostep 2 mul add eurothick louteurobox + + % circular part + /eurohctr eurowidth euroheight 2 div eurotheta cos mul sub def + /eurovctr euroheight 2 div def + newpath + eurohctr eurovctr eurovctr eurotheta 350 eurotheta sub arc + eurohctr eurovctr eurovctr eurothick sub 365 eurotheta sub eurotheta arcn + closepath fill + end +} def + +% path for @FullWidthRule symbol +/LoutRule +{ 0 0 moveto xsize 0 lineto +} def + +% path for @Box symbol +/LoutBox +{ 0 0 moveto xsize 0 lineto + xsize ysize lineto 0 ysize lineto + closepath +} def + +% path for @CurveBox symbol +/LoutCurveBox +{ xmark 0 moveto + xsize xmark sub xmark xmark 270 360 arc + xsize xmark sub ysize xmark sub xmark 0 90 arc + xmark ysize xmark sub xmark 90 180 arc + xmark xmark xmark 180 270 arc + closepath +} def + +% path for @ShadowBox symbol +/LoutShadowBox +{ xmark 2 mul 0 moveto xsize 0 lineto + xsize ysize xmark 2 mul sub lineto + xsize xmark sub ysize xmark 2 mul sub lineto + xsize xmark sub xmark lineto + xmark 2 mul xmark lineto + closepath +} def + +% set up dictionary containing margin note data: parity LoutMargSet - +/LoutMargSet +{ /LoutMargDict 12 dict def + LoutMargDict begin + /parity exch def + /matr matrix currentmatrix def + /rightx xsize def + /lefty ysize def % highest allowable point for top of next left note + /righty ysize def % highest allowable point for top of next right note + /max { 2 copy gt { pop } { exch pop } ifelse } def + /min { 2 copy lt { pop } { exch pop } ifelse } def + end +} def + +%translate coordinate system for marginal notes: type LoutMargShift - +% where type 0 is left margin, 1 is right margin, 2 is outer, 3 is inner +/LoutMargShift +{ LoutMargDict begin + + % y coordinate of top of note, in margin coords, before vertical adjust + 0 ysize transform matr itransform exch pop + + % decide whether left or right margin based on type and parity + exch [ 0 1 parity 1 parity sub ] exch get 0 eq + { + % left margin: adjust top of note downwards if overlaps previous note + lefty min + + % bottom of note is new lefty position and also translate position + ysize sub dup /lefty exch def + + % want right edge of note at coordinate zero + xsize neg exch + } + { + % right margin: adjust top of note downwards if overlaps previous note + righty min + + % bottom of note is new righty position and also translate position + ysize sub dup /righty exch def + + % want left edge of note at coordinate rightx + rightx exch + } ifelse + + % stack now contains coord of bottom left corner in margin coordinates + matr setmatrix translate + end +} def + +% create LoutPageDict with left, right, foot, top for @Place symbol users +/LoutPageSet +{ + /LoutPageDict 5 dict def + LoutPageDict begin + /matr matrix currentmatrix def + /left 0 def + 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+4183(document)s 5187(editor)s 5744(.)s 240 fnt83 5908 7423(IEEE)m +6490(Computer)s 240 fnt82 7453 7421(,)m 7560(7\21119)s 8091(\(1991\))s +8718(.)s +grestore + +grestore + +grestore + +pgsave restore +showpage + +%%Trailer +%%DocumentNeededResources: font Helvetica +%%+ font Symbol +%%+ font Times-Roman +%%+ font Times-Italic +%%+ font Times-Bold +%%DocumentSuppliedResources: procset LoutStartUp +%%+ procset LoutTabPrependGraphic +%%+ procset LoutFigPrependGraphic +%%+ procset LoutBasicSetup +%%+ encoding vec2 +%%Pages: 41 +%%EOF diff --git a/doc/design/s1_0 b/doc/design/s1_0 new file mode 100644 index 0000000..ca487ba --- /dev/null +++ b/doc/design/s1_0 @@ -0,0 +1,45 @@ +@Section + @Title { Introduction } +@Begin +@PP +Lout [1, 2] is a high-level language +for document formatting, designed and implemented by the author. The +implementation, known as Basser Lout, is a fully operational production +version written in C for the Unix operating system, +@FootNote { Unix is a trademark of "AT&T" Bell Laboratories. } +which translates Lout source code into PostScript, +@FootNote { PostScript is a trademark of Adobe Systems, Incorporated. } +a device-independent graphics rendering language accepted by many +high-resolution output devices, including most laser printers. Basser +Lout is available free of charge [3]. It includes +installation instructions, C source, seven standard packages, and complete +documentation in the form of six technical reports and a manual page. +@PP +The Lout project arose out of the author's desire to bring to document +formatting languages the elegance of expression found in programming +languages like Algol-60 and Pascal. This emphasis on expressiveness +has produced an order of magnitude reduction in the cost of developing +document formatting applications. For example, an equation formatting +application, which may be difficult or impossible to add to other +systems, can be written in Lout in a few days. +@PP +When expert users can implement such applications quickly, non-experts +benefit. Although Lout itself provides only a small kernel of carefully +chosen primitives, packages written in Lout and distributed with Basser +Lout provide an unprecedented array of advanced features in a form +accessible to non-expert users. The features include rotation and scaling, +fonts, paragraph and page breaking, displays and lists, floating figures +and tables, footnotes, chapters and sections (automatically numbered), +running page headers and footers, odd-even page layouts, automatically +generated tables of contents, sorted indexes and reference lists, +bibliographic and other databases (including databases of formats for +printing references), equations, tables, diagrams, formatting of +Pascal programs, and automatically maintained cross references. +@PP +This paper charts the evolution of Lout from conception in mid-1984 to the +public release of Basser Lout in October 1991. Lout is organized around +four key concepts -- objects, definitions, galleys, and cross references -- +and they were developed in the order listed, so this paper will treat each +in turn, discussing its design, implementation, problems, and +prospects for further improvement. +@End @Section diff --git a/doc/design/s2_0 b/doc/design/s2_0 new file mode 100644 index 0000000..ef4bea7 --- /dev/null +++ b/doc/design/s2_0 @@ -0,0 +1,14 @@ +@Section + @Title { Objects } +@Begin +@PP +The essence of any move to a higher level is the introduction of some +abstraction which serves to organize the low-level operations, +resulting in a more succinct expression of their +common combinations at the cost of some loss of detailed control. The +early part of the Lout project was spent in the development of such an +abstraction for the building blocks of documents, one which could +explain, not just the simple phenomena of words, lines, and paragraphs, +but also the alignment of columns in tables, and the complex nested +structures of equations. +@BeginSubSections diff --git a/doc/design/s2_1 b/doc/design/s2_1 new file mode 100644 index 0000000..4ee4c31 --- /dev/null +++ b/doc/design/s2_1 @@ -0,0 +1,87 @@ +@SubSection + @Tag { genesis } + @Title { The genesis of the object abstraction } +@Begin +@PP +When one examines previous document formatting systems [4] +looking for ideas for abstractions, as the author did in 1984, the Eqn +formatting language [5] stands out like a beacon. In +Eqn, a mathematical formula such as +@ID @Eq { { x sup 2 + 1 } over 4 } +is produced by typing +@ID @Code "{ x sup 2 + 1 } over 4" +in the input file; @Code sup and @Code over are binary operators, and +braces are used for grouping. This is document formatting at a very +high level, close to the language of mathematics itself, with all +reference to font changes and spacing suppressed. +@PP +Eqn provides a single data type (let us call it the {@I expression}), +built up recursively in context-free style: where one expression may appear, +any expression may appear. This approach is common in algebra and +programming languages, where its simplicity and expressiveness have long +been appreciated; but Eqn was the first language to demonstrate its +utility in document formatting. +@PP +Each expression is treated by Eqn as a rectangle with a +{@I {horizontal axis}}, used for alignment with adjacent expressions: +@ID @ShowMarks marks { horizontal } @Eq { { x sup 2 + 1 } over 4 } +The size and rendering of the expression on the printed page are +known only to the implementation, never explicitly calculated or +accessed by the user. This prohibition is +crucial to the maintenance of the context-free property in practice. In +Lout, for example, equations, figures, tables, and arbitrary objects may +be mixed together freely. This would be impossible if size information +was hidden from the implementation in user calculations. +@PP +The object abstraction of Lout is a direct descendant of the Eqn +expression. It employs the same context-free recursive style of construction, +and each object is treated by Lout as a rectangle: +@ID @Fig { +@ShowMarks { 1c @Wide ^| 2c @Wide 0.45c @High ^/ 0.35c @High } +} +The horizontal axis, called a @I { row mark } in Lout, has a +vertical analogue called a {@I {column mark}}, creating a valuable +symmetry between horizontal and vertical. Multiple column and row marks +are permitted: +@ID @OneRow @Fig { +A:: @Box margin { 0c } paint { grey } { 1.2c @Wide 0.8c @High } +|1c +B:: @Box margin { 0c } paint { grey } { 1c @Wide 0.8c @High } +/0.5c +C:: @Box margin { 0c } paint { grey } { 0.7c @Wide 0.8c @High } +|1c +D:: @Box margin { 0c } paint { grey } { 1.3c @Wide 0.8c @High } +// @Line linestyle { dashed } + from { A@W -- { 0.3 cm 0 } } + to { B@W ++ { 1.6 cm 0 } } +// @Line linestyle { dashed } + from { C@W -- { 0.3 cm 0 } } + to { D@W ++ { 1.6 cm 0 } } +// @Line linestyle { dashed } + from { A@NW ++ { 0 0.3 cm } } + to { C@SW -- { 0 0.3 cm } } +// @Line linestyle { dashed } + from { B@NW ++ { 0.3 cm 0.3 cm } } + to { D@SW ++ { 0.3 cm -0.3 cm } } +} +so that objects are able to represent tables. +@PP +This abstraction has some limitations, the most obvious being the restriction +of size calculations to rectangular bounding boxes. Non-rectangular and +disconnected shapes arise naturally in figures and in the characters of +fonts; the extension to them is conceptually straightforward and might +help to explain some fine points of layout such as kerning. However, +there are implementation and language design problems, particularly +when filling non-rectangular shapes with text, and so the author chose +to keep to Eqn's rectangles. +@PP +A more fundamental limitation of the object abstraction arises from the +inability of recursive data types to describe cross-linked structures, +which seem to require some means of naming the multiply referenced +parts. Lout is obliged to introduce additional abstractions to cope +with cross linking: galleys for inserting text into pages +(Section {@NumberOf galleys}), cross references (Section {@NumberOf cross}), +and labelled points in figure drawing [6]. An +abstraction closer to hypertext might form a more unified basis for +these features. +@End @SubSection diff --git a/doc/design/s2_2 b/doc/design/s2_2 new file mode 100644 index 0000000..f4a3818 --- /dev/null +++ b/doc/design/s2_2 @@ -0,0 +1,79 @@ +@SubSection + @Tag { lexical } + @Title { Grammatical and lexical structure } +@Begin +@PP +If objects are to be constructed like mathematical expressions, the +natural notation is a functional language based on operators, as in +Eqn. The grammar of Lout objects is accordingly +@ID @OneRow @Eq { +matrix { +object +nextcol +--> above --> above --> above --> above --> above --> above --> above --> +nextcol +{ object ``` infixop ``` object } +labove gap { "1fx" } +{ prefixop ``` object } +labove gap { "1fx" } +{ object ``` postfixop } +labove gap { "1fx" } +{ noparsop } +labove gap { "1fx" } +{ literalword } +labove gap { "1fx" } +{ @Code "{" ``` object ``` @Code "}" } +labove gap { "1fx" } +{ object ``` object } +labove gap { "1fx" } +} +} +where {@Eq {infixop}}, {@Eq {prefixop}}, {@Eq {postfixop}}, and +{@Eq {noparsop}} are identifiers naming operators which take 0, 1 +or 2 parameters, as shown, and @Eq {literalword} is a sequence of +non-space characters, or an arbitrary sequence of characters +enclosed in double quotes. Ambiguities are resolved by precedence +and associativity. +@PP +The last production allows a meaning for expressions such as +{@Code "{}"}, in which an object is missing. The value of this +@I {empty object} is a rectangle of size 0 by 0, with one column +mark and one row mark, that prints as nothing. +@PP +The second-last production generates sequences of arbitrary objects +separated by white space, called {@I paragraphs}. Ignoring +paragraph breaking for now, the natural meaning is that the two +objects should appear side by side, and Lout's parser accordingly +interpolates an infix horizontal concatenation operator (see below) +between them. This operator is associative, so the grammatical +ambiguity does no harm. However, the Algol-60 rule that white space +should be significant only as a separator is necessarily broken by +Lout in just this one place. +@PP +Algol-like languages distinguish literal strings from identifiers by +enclosing them in quotes, but literals are far too frequent in document +formatting for this to be viable. The conventional solution is to +begin identifiers with a special character, and Lout follows Scribe +[7] in using "`@'" rather than the "`\\'" of troff +[8] and @TeX [9]. +@PP +However, Lout takes the unusual step of making an initial "`@'" +optional. The designers of Eqn apparently considered such +characters disfiguring in fine-grained input like equations, and +this author agrees. The implementation is straightforward: "`@'" is +classed as just another letter, and every word is searched for in +the symbol table. If it is found, it is an identifier, otherwise it +is a literal. A warning message is printed when a literal beginning +with "`@'" is found, since it is probably a mis-spelt identifier. No +such safety net is possible for identifiers without "`@'". +@PP +Equation formatting also demands symbols made from punctuation +characters, such as @Code "+" and {@Code "<="}. It is traditional to +allow such symbols to be juxtaposed, which means that the input +@ID @Code "<=++" +for example must be interpreted within the lexical analyser by searching +the symbol table for its prefixes in the order {@Code "<=++"}, +{@Code "<=+"}, {@Code "<="}. Although this takes quadratic time, in +practice such sequences are too short to make a more sophisticated +linear method like tries worthwhile. +@End @SubSection diff --git a/doc/design/s2_3 b/doc/design/s2_3 new file mode 100644 index 0000000..341ea74 --- /dev/null +++ b/doc/design/s2_3 @@ -0,0 +1,326 @@ +@SubSection + @Tag { objects } + @Title { Basic structural operators } +@Begin +@PP +A programming language may be considered complete when it attains the +power of a Turing machine, but no such criterion seems relevant to +document formatting. Instead, as the language develops and new +applications are attempted, deficiencies are exposed and the operator set is +revised to overcome them. +@PP +Lout has a repertoire of 23 primitive operators +(Figure {@NumberOf primitives}), + +@Figure + @Caption { The 23 primitive operators of Lout, in order of +increasing precedence. } + @Tag { primitives } +@Tab + vmargin { 0.5vx } + @Fmta { @Col @I A ! @Col B } +{ +@Rowa + A { object {@Code "/"}gap object } + B { Vertical concatenation with mark alignment } +@Rowa + A { object {@Code "//"}gap object } + B { Vertical concatenation with left justification } +@Rowa + A { object {@Code "|"}gap object } + B { Horizontal concatenation with mark alignment } +@Rowa + A { object {@Code "||"}gap object } + B { Horizontal concatenation with top-justification } +@Rowa + A { object {@Code "&"}gap object } + B { Horizontal concatenation within paragraphs } +@Rowa + A { {@Code "@OneCol"} object } + B { Hide all but one column mark of @I object } +@Rowa + A { {@Code "@OneRow"} object } + B { Hide all but one row mark of @I object } +@Rowa + A { font @Code "@Font" object } + B { Render @I object in nominated font } +@Rowa + A { breakstyle @Code "@Break" object} + B { Break paragraphs of @I object in nominated style } +@Rowa + A { spacestyle @Code "@Space" object } + B { Render spaces between words in nominated style } +@Rowa + A { length {@Code "@Wide"} object } + B { Render @I object to width @I length } +@Rowa + A { length {@Code "@High"} object } + B { Render @I object to height @I length } +@Rowa + A { {@Code "@HExpand"} object} + B { Expand horizontal gaps to fill available space } +@Rowa + A { {@Code "@VExpand"} object} + B { Expand vertical gaps to fill available space } +@Rowa + A { {@Code "@HScale"} object } + B { Horizontal geometrical scaling to fill available space } +@Rowa + A { {@Code "@VScale"} object } + B { Vertical geometrical scaling to fill available space } +@Rowa + A { angle {@Code "@Rotate"} object } + B { Rotate @I object by @I angle } +@Rowa + A { PostScript {@Code "@Graphic"} object } + B { Escape to graphics language } +@Rowa + A { @Code "@Next" object } + B { Add 1 to an object denoting a number } +@Rowa + A { object @Code "@Case" alternatives } + B { Select from a set of alternative objects } +@Rowa + A { identifier @Code "&&" object } + B { Cross reference } +@Rowa + A { cross-reference @Code "@Open" object } + B { Retrieve value from cross reference } +@Rowa + A { cross-reference @Code "@Tagged" object} + B { Attach cross referencing tag to object } +} + +which has proven adequate for a wide variety of features, including equations, +tables, and page layout, and so seems to be reasonably complete in this +pragmatic sense. In this section we introduce the eight concatenation and +mark-hiding operators. To them falls the basic task of assembling complex +objects from simple ones, and they were the first +to be designed and implemented. +@PP +Many of the operators of Eqn can be viewed as building small tables. A +built-up fraction, for example, has one column and three rows +(numerator, line, and denominator). Numerous investigations of this +kind convinced the author that operators capable of assembling the rows +and columns of tables would suffice for building all kinds of objects. +@PP +The simplest objects are empty objects and literal words like +{@Code metempsychosis}, which have one column mark and one row mark: +@ID { +@ShowMarks metempsychosis +} +To place two arbitrary objects side by side, we use the infix +operator {@Code "|"}, denoting horizontal concatenation. For +example, +@ID { +@Code "USA |0.2i Australia" +} +produces the object +@ID { +@ShowMarks USA |0.2i @ShowMarks Australia +} +The row marks are merged into one, fixing the vertical position of +the objects relative to each other; their horizontal separation is +determined by the @I gap attached to the operator, in this case 0.2 +inches. We think of the gap as part of the operator, although +strictly it is a third parameter. It may be omitted, defaulting to +{@Code "0i"}. +@PP +@I {Vertical concatenation} & , denoted by the infix operator {@Code "/"}, +is the same apart from the change of direction: +@ID { +@Code "Australia /0.1i USA" +} +produces the object +@ID { +@ShowMarks Australia /0.1i +@ShowMarks USA +} +with column marks merged and a 0.1 inch gap. +@PP +Consider now what happens when horizontal and vertical are combined: +@ID @OneRow @Code { + |1m "{" USA |1m "|0.2i" |1m Australia "}" +/1vx "/0.1i" | "{" Washington | "|" | Canberra "}" +} +The two parameters of @Code "/" now have two column marks each, and +they will be merged with the corresponding marks in the other +parameter, yielding the object + +@ID @OneRow { + @BackEnd @Case { + PostScript @Yield { + @ShowMarks USA & + { 0 ymark moveto xsize 10 pt add ymark lineto [ 3 pt ] 0 setdash stroke } + @Graphic {1c @Wide } + |0.2i @ShowMarks Australia +/0.1i @ShowMarks Washington | @ShowMarks Canberra + } + PDF @Yield { + @ShowMarks USA & + { [ __mul(3, __pt) ] 0 d 0 __ymark m __add(__xsize, __mul(10, __pt)) __ymark l S } + @Graphic {1c @Wide } + |0.2i @ShowMarks Australia +/0.1i @ShowMarks Washington | @ShowMarks Canberra + } + } +} +The @Code "0.2i" gap separates columns, not individual items in +columns, so a gap attached to the second @Code "|" would serve no +purpose; any such gap is ignored. If the number of marks to be merged +differs, empty columns are added at the right to equalize the number. The +four marks protruding from the result are all available for merging +with neighbouring marks by other concatenation operators. The precedence +of @Code "|" is higher than the precedence of {@Code "/"}, so the braces +could be omitted. +@PP +When lines of text are concatenated, it is conventional to measure +their separation from baseline to baseline (mark to mark in Lout), +rather than from edge to edge as above. This idea of different +reference points for measurement evolved over the years into a +system of six @I {gap modes} (Figure {@NumberOf gapmodes}), expressed +by appending a letter to the length. For example, @Code "|0.2i" is +an abbreviation for {@Code "|0.2ie"}, meaning 0.2 inches measured +from edge to edge; @Code "|0.3ix" +produces a 0.3 inch gap measured from mark to mark and widened if +necessary to prevent overstriking; and @Code "|2.5it" places its right +parameter 2.5 inches from the current left margin, irrespective of +the position of the left parameter. There is also a choice of +eleven units of measurement (inches, centimetres, multiples of the +current font size, etc.), the most interesting being +the @Code r unit: one @Code r is the column width minus the width of +the following object, so that @Code "|1rt" produces sufficient space +to right justify the following object, and @Code "|0.5rt" to center +it. These features implement spacings needed in practice rather +than suggested by theory. They work with all five concatenation +operators, horizontal and vertical. + +@Figure + @Tag { gapmodes } + @Caption { The six gap modes (@I length is any length). Hyphenation +mode has an extra property not shown here. } +@Fig { +{ /2.5vx Edge-to-edge |0.3i {@Code "|"} &1p {@I length} &1p {@Code e} + /4.2vx Hyphenation |0.3i {@Code "|"} &1p {@I length} &1p {@Code h} + /4.2vx Overstrike |0.3i {@Code "|"} &1p {@I length} &1p {@Code o} + /4.2vx Mark-to-mark |0.3i {@Code "|"} &1p {@I length} &1p {@Code x} + /4.2vx Kerning |0.3i {@Code "|"} &1p {@I length} &1p {@Code k} + /4.2vx Tabulation |0.3i {@Code "|"} &1p {@I length} &1p {@Code t} +} +||0.5i +@Box margin { 0c } 6c @Wide 14.5c @High 9p @Font +{ + @OneRow { + @At { 1c @Wide 0.5c @High } @Put { @LBox 0.2co } + @At { 4c @Wide 0.5c @High } @Put { @LBox 0.5co } + @At { 2.2c @Wide 1.4c @High } @Put { @DoubleArrow 1.8c } + @At { 2.2c @Wide 1.6c @High } @Put { 1.8c @Wide { &0.5rt @I length } } + } + //4vx + @OneRow { + @At { 1c @Wide 0.5c @High } @Put { @LBox 0.2co } + @At { 4c @Wide 0.5c @High } @Put { @LBox 0.5co } + @At { 2.2c @Wide 1.4c @High } @Put { @DoubleArrow 1.8c } + @At { 2.2c @Wide 1.6c @High } @Put { 1.8c @Wide { &0.5rt @I length } } + } + //4vx + @OneRow { + @At { 1c @Wide 0.5c @High } @Put { @LBox 0.2co } + @At { 4c @Wide 0.5c @High } @Put { @LBox 0.5co } + @At { 1.2c @Wide 1.5c @High } @Put { @DoubleArrow 3.3c } + @At { 1.2c @Wide 1.7c @High } @Put { 3.3c @Wide { &0.5rt @I length } } + } + //4vx + @OneRow { + @At { 1c @Wide 0.5c @High } @Put { @LBox 0.2co } + @At { 4c @Wide 0.5c @High } @Put { @LBox 0.5co } + @At { 1.2c @Wide 1.5c @High } @Put { @DoubleArrow 3.3c } + @At { 1.2c @Wide 1.7c @High } + @Put 3.3c @Wide { |0.5rt @Eq { max(length, a+b) } } + @At { 1.2c @Wide 0.4c @High } @Put { @DoubleArrow 1.0c } + @At { 1.2c @Wide 0.2c @High } @Put { 1.0c @Wide { &0.5rt @I a } } + @At { 4c @Wide 0.4c @High } @Put { @DoubleArrow 0.5c } + @At { 4c @Wide 0.2c @High } @Put { 0.5c @Wide { &0.5rt @I b } } + } + //4.5vx + @OneRow { + @At { 1c @Wide 0.5c @High } @Put { @LBox 0.2co } + @At { 4c @Wide 0.5c @High } @Put { @LBox 0.5co } + @At { 1.2c @Wide 1.5c @High } @Put { @DoubleArrow 3.3c } + @At { 1.2c @Wide 1.7c @High } + @Put { 3.3c @Wide { |0.5rt @Eq { max(length, a, b) } } } + @At { 1.2c @Wide 0.4c @High } @Put { @DoubleArrow 1.0c } + @At { 1.2c @Wide 0.2c @High } @Put { 1.0c @Wide { &0.5rt @I a } } + @At { 4c @Wide 0.4c @High } @Put { @DoubleArrow 0.5c } + @At { 4c @Wide 0.2c @High } @Put { 0.5c @Wide { &0.5rt @I b } } + } + //4vx + @OneRow { + @At { 1c @Wide 0.5c @High } @Put { @LBox 0.2co } + @At { 4c @Wide 0.5c @High } @Put { @LBox 0.5co } + @At { 0.0c @Wide 1.6c @High } @Put { @DoubleArrow 4.0c } + @At { 2.8c @Wide 1.8c @High } @Put { @I length } + } + //5vx + @DoubleArrow 6c + //0.1c |0.5rt @I { current bound } +} +} + +@PP +When we construct a built-up fraction, the result has three row marks, but +only the second should be visible outside the object: +@ID @Eq { @ShowMarks { X over Y } } +This is a common problem, and accordingly a @Code "@OneRow" operator was +introduced for hiding all but one of the row marks of its +parameter. Normally, the first mark is the survivor, but a later mark can +be chosen by prefixing @Code "^" to the preceding concatenation operator: +@ID @Code "@OneRow { X ^/2p @HLine /2p Y }" +has the desired result, where {@Code "2p"} is two points and @Code "@HLine" +is an easy combination of Lout's graphics operators. A similar operator, +{@Code "@OneCol"}, hides column marks. +@PP +A variant of @Code "/" called @Code "//" is provided which performs +vertical concatenation but ignores all column marks and simply +left-justifies its two parameters: +@ID @OneRow @Code { +"Heading //0.1i" +"A |0.2i B /0.1i" +"C | D" +} +has result +@ID { Heading //0.1i A |0.2i B /0.1i C | D } +showing that spanning columns in tables motivate the inclusion of this +operator. There is an analogous @Code "||" operator. The author +would have preferred to leave out these operators, since they +complicate the implementation, and it is interesting to examine the +prospects of doing so. +@PP +The @Code "//" operator is formally redundant, because in general +the expression @Code "x // y" can be replaced by +@ID @OneRow @Code { +"@OneCol { | x } /" +"@OneCol { | y }" +} +for any objects {@Code x} and {@Code y}. By concatenating an empty +object at the left of @Code x and hiding all but that empty object's +column mark, we effectively shift {@Code x}'s column mark to its left +edge. The same goes for {@Code y}, so the @Code "/" operator has just +one column mark to merge, at the extreme left, and its effect is +indistinguishable from {@Code "//"}. +@PP +Unfortunately, if @Code y consists of two rows separated by {@Code "/"}, +as in the example above, both rows must be placed inside the +{@Code "@OneCol"}, and the table cannot be entered in the simple +row-by-row manner that non-expert users naturally expect. Another +advantage of @Code "//" is that its left parameter can be printed +before its right parameter is known; this is important when the left +parameter is an entire page. +@PP +The fifth and final concatenation operator, {@Code "&"}, is an explicit +version of the horizontal concatenation operator interpolated when +objects are separated by white space. It is formally identical to +@Code "|" except for taking higher precedence and being subject to +replacement by @Code "//1vx" during paragraph breaking +(Section {@NumberOf style}). +@End @SubSection diff --git a/doc/design/s2_4 b/doc/design/s2_4 new file mode 100644 index 0000000..38d25e7 --- /dev/null +++ b/doc/design/s2_4 @@ -0,0 +1,345 @@ +@SubSection + @Tag { objects.impl } + @Title { Implementation of objects and concatenation } +@Begin +@PP +In this section we discuss the implementation of objects and concatenation, +and especially mark alignment. The first step is to use an operator +precedence parser to convert input such as +@ID @Code "a |0.5i b /0.2i c | d" +into parse trees such as +@ID @Eq { +@Fig { +@Tree { +@Node @FCircle fraction +@FirstSub { + @Node @FCircle bar + @FirstSub { @Node @FCircle a } + @NextSub { @Node @FEllipse 0.5i } + @NextSub { @Node @FCircle b } +} +@NextSub { @Node @FEllipse 0.2i } +@NextSub { + @Node @FCircle bar + @FirstSub { @Node @FCircle c } + @NextSub { @Node @FCircle } + @NextSub { @Node @FCircle d } +} +} +} +} +Missing objects are replaced by empty objects, and sequences of +concatenation operators are consolidated: +@ID @Eq { +@Fig { +@Tree { +@Node @FCircle bar +@FirstSub { @Node @FCircle a } +@NextSub { @Node @FEllipse 0.2i } +@NextSub { + @Node @FCircle bar + @FirstSub { @Node @FCircle c } + @NextSub { @Node @FEllipse 0.3i } + @NextSub { @Node @FCircle d } +} +} +} +&2m ==> &2m +@Fig { +@Tree { +@Node @FCircle bar +@FirstSub { @Node @FCircle a } +@NextSub { @Node @FEllipse 0.2i } +@NextSub { @Node @FCircle c } +@NextSub { @Node @FEllipse 0.3i } +@NextSub { @Node @FCircle d } +} +} +} +to make manifest their associativity and reduce the depth of the tree +for efficiency later. +@PP +The required semantic information is the size of each subobject, +consisting of four integers: width to left and right of the +distinguished column mark, and height above and below the distinguished +row mark. These numbers are always non-negative in Basser Lout, but +this restriction is unnecessary and should be dropped. +@PP +For the leaves, which are simple words, the numbers are obtained from +font tables. For the higher levels we apply recursive rules. Suppose +that @Eq { hgap(x, g, y) } returns the desired distance between the +column marks of objects @Eq { x } and @Eq { y } when they are separated by +gap @Eq { g }: @Eq { right(x) + length(g) + left(y) } when the gap mode is +edge-to-edge, the larger of @Eq { length(g) } and +@Eq { right(x) + left(y) } when the mode is mark-to-mark, and so on. Given +an object +@ID @Eq { +X = x sub 1 ````` bar g sub 1 ````` ... ````` { "-2p" @Font "^"}bar g sub i-1 +````` x sub i ````` ... ````` bar g sub n-1 ````` x sub n +} +we may calculate its size as follows: +@ID @Eq { +left(X) ^= left( x sub 1 ) + hgap( x sub 1 , g sub 1 , x sub 2 ) ++ ... + hgap( x sub i-1 , g sub i-1 , x sub i ) +/1.4vx +right(X) ^= hgap( x sub i , g sub i , x sub i+1 ) ++ ... + hgap( x sub n-1 , g sub n-1 , x sub n ) + right( x sub n ) +/1.4vx +"above"(X) ^= "above"(x sub 1 ) up ... up "above"(x sub n ) +/1.4vx +"below"(X) ^= "below"(x sub 1 ) up ... up "below"(x sub n ) +} +where @Eq { non up } returns the larger of its two parameters. Similar +formulas are easily derived for the other operators. +@PP +For purposes of exposition we will now make the simplifying +assumptions that all gaps are {@Code "0i"}, all column marks lie at +the left edge, and all row marks lie at the top edge. Then the size +of each object can be expressed by just two numbers, width and +height, and the four formulas reduce to +@ID @Eq { +width( x sub 1 rel bar ... rel bar x sub n ) ^= +width( x sub 1 ) + ... + width( x sub n ) +/1.4vx +height( x sub 1 rel bar ... rel bar x sub n ) ^= +height( x sub 1 ) up ... up height( x sub n ) +} +The corresponding formulas for vertical concatenation are +@ID @Eq { +width( x sub 1 rel "/" ... rel "/" x sub n ) ^= +width( x sub 1 ) up ... up width( x sub n ) +/1.4vx +height( x sub 1 rel "/" ... rel "/" x sub n ) ^= +height( x sub 1 ) + ... + height( x sub n ) +} +According to these formulas, the height of +@ID @Eq { @Fig { @Tree { +@Node @FCircle fraction +@LeftSub { + @Node @FCircle bar + @LeftSub { @Node @FCircle a } + @RightSub { @Node @FCircle b } +} +@RightSub { + @Node @FCircle bar + @LeftSub { @Node @FCircle c } + @RightSub { @Node @FCircle d } +} +}}} +is +@ID @Eq { +[ height(a) up height(b)] + [ height(c) up height(d)] +} +which is correct, but for width they yield +@ID @Eq { +[ width(a) + width(b)] up [ width(c) + width(d)] +} +which is not, since it does not take the merging of column marks into +account. The asymmetry between horizontal and vertical has come +about because the row entries, such as @Eq {a} and {@Eq {b}}, are +adjacent in the tree, but the column entries, such as @Eq {a} and +{@Eq {c}}, are not. It would be possible to solve this cross-linking +problem by augmenting the size information stored in each node to +record the number of marks and the size of each, but the author has +preferred the following method which makes structural changes to the +tree instead. +@PP +If @Eq { a } and @Eq { c } share a column mark, they each might as well +have width { @Eq {width(a) up width(c) }}, since all width calculations +apply to entire columns. Accordingly, we introduce a new operator, +@Eq {COL}, defined by +@ID @Eq { width( x sub 1 bin COL ... bin COL x sub n ) = +width( x sub 1 ) up ... up width( x sub n ) +} +and replace both @Eq { a } and @Eq { c } by {@Eq { a bin COL c }}. To +prevent @Eq { COL } operators from disturbing height calculations, we +define a binary operator called @Eq { SPLIT } by +@ID @Eq { width( x bin SPLIT y) ^= width(x) +/1.4vx +height( x bin SPLIT y) ^= height(y) } +which switches height and width calculations onto different +subtrees. Then the transformation +@ID @Eq { +@Fig { @Tree { + @Node @FCircle a +}} +&2m ==> &2m +@Fig { @Tree { + @Node @FEllipse SPLIT + @LeftSub { + @Node @FEllipse COL + @LeftSub { @Node @FCircle a } + @RightSub { @Node @FCircle c } + } + @RightSub { @Node @FCircle a } +}} +} +# where @Eq { S } denotes a @Eq { SPLIT } node and @Eq { C } denotes a +# @Eq { COL } node, +widens @Eq { a } to @Eq {width(a) up width(c) } without affecting its height; +it is applied to every object that shares its column mark with at least +one other object. A similar transformation involving a @Eq { ROW } operator +deals with shared row marks. The effect on our little table is to replace +@ID @Eq { @Fig { @Tree { +@Node @FCircle fraction +@LeftSub { + @Node @FCircle bar + @LeftSub { @Node @FCircle a } + @RightSub { @Node @FCircle b } +} +@RightSub { + @Node @FCircle bar + @LeftSub { @Node @FCircle c } + @RightSub { @Node @FCircle d } +} +}}} +by +@ID @Eq { @Fig maxlabels { "70" } { @Tree hmargin { "0.1c" } { +@Node @FCircle fraction +@FirstSub { + @Node @FCircle bar + @FirstSub { + @Node @FEllipse SPLIT + @FirstSub { + @Node @FEllipse COL + @FirstSub { @Node @FCircle a } + @NextSub { @Node @FCircle c } + } + @NextSub { + @Node @FEllipse ROW + @FirstSub { @Node @FCircle a } + @NextSub { @Node @FCircle b } + } + } + @NextSub { + @Node @FEllipse SPLIT + @FirstSub { + @Node @FEllipse COL + @FirstSub { @Node @FCircle b } + @NextSub { @Node @FCircle d } + } + @NextSub { + @Node @FEllipse ROW + @FirstSub { @Node @FCircle a } + @NextSub { @Node @FCircle b } + } + } +} +@NextSub { + @Node @FCircle bar + @FirstSub { + @Node @FEllipse SPLIT + @FirstSub { + @Node @FEllipse COL + @FirstSub { @Node @FCircle a } + @NextSub { @Node @FCircle c } + } + @NextSub { + @Node @FEllipse ROW + @FirstSub { @Node @FCircle c } + @NextSub { @Node @FCircle d } + } + } + @NextSub { + @Node @FEllipse SPLIT + @FirstSub { + @Node @FEllipse COL + @FirstSub { @Node @FCircle b } + @NextSub { @Node @FCircle d } + } + @NextSub { + @Node @FEllipse ROW + @FirstSub { @Node @FCircle c } + @NextSub { @Node @FCircle d } + } + } +} +}}} +In fact, common subexpressions are identified (trivially) and the result +is a directed acyclic graph; each affected leaf has two parents, one for +width and one for height; and each @Eq { COL } or @Eq { ROW } node has +one parent and one child for each object lying on the corresponding +mark. The data structure roughly doubles in size, and this occurs only +rarely in practice. +@PP +This method can cope with any legal input, including +@ID @OneRow @Code { +"{ a // c | d } | { b / e }" +"/ { f / i } | { g | h // j }" +} +which produces overlapping spanning columns: +@ID @I @Fig { + @FBox margin { 0.2c } width { 1.6c } 1.2f @Font a | + @FBox margin { 0.2c } width { 0.6c } 1.2f @Font b | +// @FBox margin { 0.2c } width { 0.6c } 1.2f @Font c | + @FBox margin { 0.2c } width { 0.6c } 1.2f @Font d | + @FBox margin { 0.2c } width { 0.6c } 1.2f @Font e | +// @FBox margin { 0.2c } width { 0.6c } 1.2f @Font f | + @FBox margin { 0.2c } width { 0.6c } 1.2f @Font g | + @FBox margin { 0.2c } width { 0.6c } 1.2f @Font h | +// @FBox margin { 0.2c } width { 0.6c } 1.2f @Font i | + @FBox margin { 0.2c } width { 1.6c } 1.2f @Font j | +} +The boxes have been added to clarify the structure. The width of this +object is formally +@ID @Eq { ((width(a) up (x + y)) + z) up (x + ((y + z) up width(j))) } +where +@IL +@ListItem @Eq { x = width(c) up width(`f`) up width(i) } +@ListItem @Eq { y = width(d`) up width(g) } +@ListItem @Eq { z = width(b) up width(e) up width(h) } +@EL +It seems clear that @Eq { y } at least must appear twice in any +expression for the width of this object made out of simple addition +and maxing operations, showing that an ordinary tree +structure is insufficient for overlapping spanning columns. The Basser +Lout interpreter actually rejects such structures, owing to the author's +doubts about the implementability of @I Constrained and @I AdjustSize +(Section {@NumberOf constraints}) on them; but with hindsight this caution +was unnecessary. +@PP +The directed acyclic graph is ordered in the sense that the order of +the edges entering and leaving each node matters. The structure is +highly dynamic, and traversals both with and against the arrows are +required. After a few ad-hoc attempts to extend the usual tree +representation had failed, the author developed a representation based +on doubly linked lists of records denoting links, whose flexibility more +than compensated for the somewhat excessive memory consumption. For example, +@ID @Eq { @Fig { + A:: @FCircle a |2c |2c B:: @FCircle b +/1.5c C:: @FCircle c | D:: @FCircle d +// A @JoinFigures arrow { forward } C +// A @JoinFigures arrow { forward } D +// B @JoinFigures arrow { forward } D +}} +is represented by +@CD @Eq { @Fig maxlabels { "300" } { +A:: @DagBox mid { @BlackDot } base { a } |2c |2c |2c |2c +B:: @DagBox mid { @BlackDot } base { b } +/1c L:: @DagBox top { @BlackDot } mid { @BlackDot } base { LK } +| M:: @DagBox top { @BlackDot } mid { @BlackDot } base { LK } +| | N:: @DagBox top { @BlackDot } mid { @BlackDot } base { LK } +/1c +C:: @DagBox top { @BlackDot } base { c } | | +D:: @DagBox top { @BlackDot } base { d } +// @TVShape nw { A@MID@CTR } ne { A@MID@CTR } sw {L@MID@CTR } se { M@MID@CTR } +// @TVShape nw { L@TOP@CTR } ne { L@TOP@CTR } sw {C@TOP@CTR } se { C@TOP@CTR } +// @TVShape nw { M@TOP@CTR } ne { N@TOP@CTR } sw {D@TOP@CTR } se { D@TOP@CTR } +// @TVShape nw { B@MID@CTR } ne { B@MID@CTR } sw {N@MID@CTR } se { N@MID@CTR } +}} +where @Eq { LK } tags a record representing a link. The first list +in any node contains all the incoming links, the second contains the +outgoing ones. The node serves as the header for both lists. The +required operations reduce to simple appends, deletes, and traversals +of doubly linked lists, all having small constant cost. There is a +highly tuned memory allocator, and care is taken to dispose of each node +when the last incoming link is deleted, so that there is no need for +garbage collection. +@PP +In normal use the number of nodes at higher levels of the dag is small +in comparison with the leaves and their incoming links, so we may +estimate the space complexity at about 60 bytes per input word (20 bytes +per link, 40 per leaf node). Careful optimization could easily halve +this, but since memory is reclaimed after printing each page there is +little need. +@End @SubSection diff --git a/doc/design/s2_5 b/doc/design/s2_5 new file mode 100644 index 0000000..87d826b --- /dev/null +++ b/doc/design/s2_5 @@ -0,0 +1,90 @@ +@SubSection + @Tag { style } + @Title { Context-sensitive attributes of objects } +@Begin +@PP +Although we are free to place any object in any context, the context +must influence the appearance of the object, since otherwise +@ID @Code "A short paragraph of text." +could not appear in a variety of fonts, column widths, etc. This +influence cannot take the purely static form that block-structured +languages use to associate values with identifiers, for then an operator +could not influence the appearance of its parameters; and a state +variable solution is not compatible with the overall functional design. +@PP +The information needed from the context seems quite limited, comprising +the font family, face, and size to use, the style of paragraph breaking +required, how much space to substitute between the words of paragraphs, +and how much horizontal and vertical space is available to receive the +object. These four items constitute the so-called `style information' +of Lout. As graphics rendering hardware improves, the style information +will probably grow to include colour and texture information. +@PP +The way to deal with fonts at least is very clear: +@ID @Code "{ Times Slope 12p } @Font { Hello, world }" +should have result +@ID { { Times Slope 12p } @Font { Hello, world } } +Lout also provides @Code "@Break" and @Code "@Space" symbols for +controlling the paragraph breaking and space styles mentioned +above. These work in the same way, returning their right +parameters in the style of their left. The implementation is very +simple: one merely broadcasts the style information down into the parse +tree of the right parameter. A font, for example, is converted to an +8-bit internal name and stored in each leaf, while a breaking style is +stored in the root node of each paragraph. +@PP +The same language design can be used for available width and height, +only here the implementation is much more demanding: +@ID @Code { +"2i @Wide {" +"(1) |0.1i An example" +"containing a small" +"paragraph of filled text." +"}" +} +is guaranteed to be two inches wide: +@ID { +2i @Wide { +(1) |0.1i An example +containing a small +paragraph of filled text. +} +} +One must calculate that 1.9 inches minus the width of @Code "(1)" is +available +to the paragraph, and break it accordingly; Basser Lout does this in two +stages. In the first, upward-moving stage, widths are calculated using the +formulae of Section {@NumberOf objects}, which assume that available +space is infinite. If the upward movement reaches a @Eq { WIDE } +node, corresponding to a @Code "@Wide" operator, and +the calculated width exceeds that allowed, a second, downward-moving stage +is initiated which attempts to reduce the width by finding and breaking +paragraphs. This second stage is quite routine except at @Code "|" nodes, +whose children are the columns of a table. It is necessary to apportion +the available width (minus inter-column gaps) among the columns. Basser +Lout leaves narrow columns unbroken and breaks the remaining columns to +equal width, using up all of the available space. +@PP +The size of an object is not clearly determined when the upward-moving +size is less than the downward-moving available space, and the object +contains constructs that depend on available space (e.g. right +justification). For example, in +@ID @Code "2i @Wide { Heading // a |1rt b }" +it seems natural to assign a width of two inches to the subobject +@Code "a |1rt b" because of the right justification, but it would be +equally plausible if the width of @Code Heading was assigned to the +subobject instead. The author is conscious of having failed to resolve +this matter properly; an extra operator for controlling available space +is probably necessary. +@PP +The actual paragraph breaking is just a simple transformation on the +parse tree; the real issue is how to describe the various styles: ragged +right, adjusted, outdented, and so on. Their diversity suggests that +they should somehow be defined using more basic features; but then there +are algorithms for high-quality paragraph breaking, which presumably +must be built-in. This dilemma was not clearly grasped by the author in +1985, and he included a built-in paragraph breaker, with the @Code +"@Break" operator selecting from a fixed set of styles. A much better +solution based on galleys will be given in Section {@NumberOf horizontal}, +but, regrettably, it is not implemented. +@End @SubSection diff --git a/doc/design/s2_9 b/doc/design/s2_9 new file mode 100644 index 0000000..648a1b6 --- /dev/null +++ b/doc/design/s2_9 @@ -0,0 +1,2 @@ +@EndSubSections +@End @Section diff --git a/doc/design/s3_0 b/doc/design/s3_0 new file mode 100644 index 0000000..3f42ff5 --- /dev/null +++ b/doc/design/s3_0 @@ -0,0 +1,10 @@ +@Section + @Title { Definitions } +@Begin +@PP +The need to provide a means of packaging useful pieces of code for easy +repeated use was recognised in the very earliest programming +languages. This need is even more acute in document formatting, if that +is possible, because the majority of users are not programmers and do +not understand the code they invoke. +@BeginSubSections diff --git a/doc/design/s3_1 b/doc/design/s3_1 new file mode 100644 index 0000000..2fb44c6 --- /dev/null +++ b/doc/design/s3_1 @@ -0,0 +1,76 @@ +@SubSection + @Tag { operators } + @Title { Operators } +@Begin +@PP +It is evident from the example of Eqn that user-defined operators are +needed that mimic the primitive ones in taking objects as parameters +and returning objects as results. For example, to define a superscript +operator so that +@ID @Code "2 sup n" +appears as {@Eq {2 sup @R n}}, the following operator definition may +be used: +@ID @OneRow @Code { +"def sup" +" precedence 50" +" associativity right" +" left x" +" right y" +"{" +" @OneRow { | {-2p @Font y} ^/0.5fk x }" +"}" +} +The @Code "sup" operator has precedence 50, is right associative, takes +two objects as parameters passed on the left and right, and returns the +object between braces as result. This object has the structure +@ID @I +2p @Font { +| @ShowMarks @Code y / @ShowMarks @Code x +} +but with the first row mark hidden by the @Code "@OneRow" operator, +and @Code y two points smaller than it would otherwise have been. The +length @Code "0.5f" specifies half the current font size; Figure +{@NumberOf gapmodes} describes the @Code k gap mode. In the Eq equation +formatting package [10] the equation as a whole is +set in italic font, and @Code 2 is an identifier whose body contains +a font change back to Roman. The digits @Code 0 to @Code 9 are classed +as punctuation characters, permitting @Code 234 for example to be +interpreted as a sequence of three identifiers. +@PP +These definitions are easily implemented by a standard symbol table +and an operator precedence parser. Algol block structure with the +usual scope rules was adopted as a matter of course. +@PP +Operators are limited to at most two parameters, left and +right, and the parameters cannot be given default values. @I Named +parameters solve both problems: +@ID @OneRow @Code { +"def @Preface" +" named @Tag {}" +" named @Title { Preface }" +" right @Body" +"{" +" Bold @Font @Title" +" //0.3v @Body" +"}" +} +The default value appears just after the parameter's declaration, +between braces. Invocations have a natural syntax: +@ID @OneRow @Code { +"@Preface" +" @Title { About this book }" +"{" +" Few observers would have supposed in 1984, that ..." +"}" +} +with the actual named parameters following directly after the +operator, before any right parameter. In this example, @Code "@Tag" +will receive its default value, and a less expert user could safely +omit the @Code "@Title" parameter as well. +@PP +Lout permits named parameters to have parameters, a feature with +applications to bibliographic databases, running headers, and other +places where a format has to be supplied before content is +known. One could go further and provide a complete lambda calculus, +with functions as first-class objects, provided care was taken not +to intimidate the non-expert user. +@End @SubSection diff --git a/doc/design/s3_2 b/doc/design/s3_2 new file mode 100644 index 0000000..0c5fd70 --- /dev/null +++ b/doc/design/s3_2 @@ -0,0 +1,113 @@ +@SubSection + @Tag { recursion } + @Title { Recursion and page layout } +@Begin +@PP +Design and implementation should proceed together in exploratory projects, +since otherwise the design too easily becomes unrealistic. Sometimes the +implementation does more than its designer intended. The author wrote the +following purely as a testing scaffold: +@ID @OneRow @Code { +"def @Page right x" +"{" +" 8i @Wide 11i @High" +" {" +" //1i ||1i x ||1i" +" //1i" +" }" +"}" +} +Only afterwards did he realize its significance: the concept of a page +had been defined outside the implementation, removing the need for +commands for setting page width and height, margins, and so on. +@PP +Defining a sequence of pages is harder, since their number is not known +in advance. A simple version of this same problem is afforded by the +leaders found in tables of contents: +@ID { +4i @Wide { Chapter 7 @Leaders 53 } +} +This seemed to require recursion, specifically the definition +@ID @Code { +"def @Leaders { .. @Leaders }" +} +Note that both @Code ".." and @Code "@Leaders" are objects, so the two +spaces separating them are significant. No base case is given, and indeed +we have no boolean or conditional operators with which to express it; +but we can adopt the implicit base `if space is not sufficient, delete +{@Code "@Leaders"} and any preceding space'. Then the expression +@ID @Code "4i @Wide { Chapter 7 @Leaders 53 }" +will produce the object shown above. It is hard to see how this base +could be made explicit, without violating the general principle of +keeping all size information internal. In the implementation, +@Code "@Leaders" remains unexpanded while sizes are being +calculated; then it is treated similarly to a receptive symbol, with +its body as an incoming galley (Section {@NumberOf flushing}). +@PP +With this settled, it is now clear how to define a document which is a +numbered sequence of pages. Let @Code "@Next" be a prefix operator +which returns its parameter plus one. Then +@ID @OneRow @Code { +"def @PageList" +" right @PageNum" +"{" +" @Page {" +" |0.5rt - @PageNum -" +" //1v @TextPlace" +" //1rt @FootSect" +" }" +" //" +" @PageList @Next @PageNum" +"}" +} +when invoked in the expression {@Code "@PageList 1"}, has for its result +the potentially infinite object +@ID @OneRow { +@LittlePage { +|0.5rt - 1 - +//1.2vx @Code "@TextPlace" +//1rt @Code "@FootSect" +} +// +@LittlePage { +|0.5rt - 2 - +//1.2vx @Code "@TextPlace" +//1rt @Code "@FootSect" +} +//0.2c +8p @Font @Code "@PageList 3" +} +Similarly, we may define @Code "@FootSect" like this: +@ID @OneRow @Code { +"def @FootSect" +"{" +" def @FootList" +" right @Num" +" {" +" @FootPlace" +" //1v" +" @FootList @Next @Num" +" }" +"" +" 1i @Wide @HLine" +" //1v" +" @FootList 1" +"}" +} +so that an invocation of @Code "@FootSect" produces +@ID @OneRow @Code { +1i @Wide @HLine +"@FootPlace" +"@FootPlace" +"@FootPlace" +"..." +} +The expansion process is very similar to a BNF derivation, and would be +attempted only on demand. +@PP +Clearly, deciding which expansions to take and replacing @Code "@TextPlace" +and {@Code "@FootPlace"} by the appropriate actual text will not be easy; +this is the subject of Section {@NumberOf galleys}. The important point +for now is that we have here a very simple and flexible method of specifying +the layout of pages, which requires no specialized language features. +@End @SubSection diff --git a/doc/design/s3_3 b/doc/design/s3_3 new file mode 100644 index 0000000..d04a8db --- /dev/null +++ b/doc/design/s3_3 @@ -0,0 +1,143 @@ +@SubSection + @Tag { modules } + @Title { Modules } +@Begin +@PP +It is well accepted that the visibility of symbols is not adequately +controlled by Algol block structure. The author is aware of several +major problems of this kind in document formatting. +@PP +One problem is that some symbols should be visible only within +restricted parts of a document. For example, we naturally expect +equation formatting to be accomplished like this: +@ID @OneRow @Code { +"surrounding text" +"@Eq { {x sup 2 + 1} over 4 }" +"surrounding text" +} +with the symbols {@Code "sup"}, {@Code "over"}, etc., visible only within +the equation, not in the surrounding text. +@PP +It seems natural to define these symbols within {@Code "@Eq"}, since +they are local to equations. It only remains then to decree that +symbols local to @Code "@Eq" are to be visible within its actual right +parameter, and this is done by replacing the right formal parameter with a +@I body parameter: +@ID @OneRow @Code { +"export sup over" +"def @Eq" +" body @Body" +"{" +" def sup ..." +" def over ..." +"" +" Slope @Font @Body" +"}" +} +The @Code export clause lists the identifiers which are permitted to be +visible outside their usual range, the body of {@Code "@Eq"}; and the +@Code body declaration imports them into (makes them visible within) +the actual right parameter of each invocation of {@Code "@Eq"}. This +arrangement has proven very convenient for defining a variety of +special-purpose packages. +@PP +Another problem arises when global symbols, such as the ones used for +headings and paragraph separators, call on values that the non-expert +user will need to modify, such as the initial font or paragraph +indent. These values are like parameters of the document as a whole, so +it is natural to try this: +@ID @OneRow @Code { +"export @Heading @PP ..." +"def @BookLayout" +" named @InitialFont { Times Base 12p }" +" named @InitialBreak { adjust 14p }" +" named @ColumnWidth { 6i }" +" ..." +"{" +" def @Heading ..." +" def @PP ..." +"}" +} +Now @Code "@Heading" and @Code "@PP" may invoke @Code "@InitialFont" +and the other parameters. To make @Code "@Heading" and @Code "@PP" +visible throughout the document, we need only add a body parameter to +@Code "@BookLayout" and present the entire document as +@ID @OneRow @Code { +"@BookLayout" +" @InitialFont { Helvetica Base 10p }" +" @InitialBreak { adjust 12p }" +"{" +" The document." +"}" +} +but for practical reasons given below we prefer not to enclose the +entire document in braces. Instead, we write +@ID @OneRow @Code { +"@Use { @BookLayout" +" @InitialFont { Helvetica Base 10p }" +" @InitialBreak { adjust 12p }" +"}" +"The document." +} +which has the same effect: @Code "@Use" makes the exported symbols of +@Code "@BookLayout" visible for the remainder of the document, and is +permitted only at the beginning. +@PP +The third feature that affects visibility, and which will prove useful +for cross referencing (Section {@NumberOf cross}), is the @Code "@Open" +symbol. It makes the exported symbols of its left parameter visible +within its right parameter, and is therefore similar to the Pascal @Code +with statement. +@PP +It could be argued that Lout is over-supplied with these visibility modifying +features: the body parameter, @Code "@Use" and @Code "@Open" do not seem +sufficiently different from each another. The @Code "@Open" symbol is +the most general, being capable of replacing the other two. For +example, +@ID @OneRow @Code { +"@Use { x }" +"@Use { y }" +"Body of document" +} +can be replaced by +@ID @OneRow @Code { +"x @Open {" +"y @Open {" +"Body of document" +"}}" +} +and, taking the @Code "@Eq" symbol above as example, we could eliminate +its body parameter, add +@ID @Code "def @Body right x { Slope @Font x }" +to the exported definitions of {@Code "@Eq"}, and replace +@ID @Code "@Eq { object }" +by +@ID @Code "@Eq @Open { @Body { object } }" +If @Code "@Eq" is a galley (Section {@NumberOf galleys}), @Code "@Body" +must take over that function. But one would not want to write these +clumsy expressions in practice, and the enclosure of large quantities +of input in extra braces could cause Basser Lout to run out of memory +(Section {@NumberOf lookahead}). +@PP +A quite separate kind of visibility problem arises when expert +users wish to define an object or operator for repeated use within, say, +equations: +@ID @Code "def isum { sum from i=1 to n }" +As it stands this can only be placed within the @Code "@Eq" package itself, +where @Code "sum" and the other symbols are visible, but it is not desirable +to modify the source code of a standard package. Lout provides an +@Code "import" clause to solve this problem: +@ID @OneRow @Code { +"import @Eq" +"def isum { sum from i=1 to n }" +} +may appear after @Code "@Eq" is defined, and it will make the exported symbols +of @Code "@Eq" visible within the body of {@Code "isum"}. This feature +complicates the treatment of environments (Section {@NumberOf defs.impl}), +and even introduces an insecurity, when @Code isum is invoked outside an +equation. A simpler approach would be to allow only one symbol in an +@Code import clause, and treat the following definition exactly like a +local definition of that symbol; but then it would not be possible +to define symbols using the resources of more than one of the standard +packages. +@End @SubSection diff --git a/doc/design/s3_4 b/doc/design/s3_4 new file mode 100644 index 0000000..7b0f5bc --- /dev/null +++ b/doc/design/s3_4 @@ -0,0 +1,51 @@ +@SubSection + @Tag { defs.impl } + @Title { Implementation of definitions } +@Begin +@PP +Input is processed by a hybrid parser which employs operator precedence +for objects and simple recursive descent for the headers of +definitions. A symbol table stores the body of each definition as a +parse tree, except for macros which are lists of tokens, and manages the +usual stack of static scopes, accepting @I PushScope and @I PopScope +operations as the parser enters and leaves scope regions, including +actual body parameters and the right parameter of the @Code "@Open" +operator. +@PP +As the parse proceeds, a complete call graph is constructed, recording, +for each symbol, which symbols are invoked within its body. Immediately +after the last definition is read, the transitive closure of the call +graph is computed, and used to determine whether each non-parameter +symbol is recursive or receptive (Section {@NumberOf galleys}), and +whether each parameter is invoked exactly once or not. +@PP +Purely functional systems may evaluate symbol invocations in applicative +order (where parameters are evaluated before substitution into bodies), +or in normal order (substitution before evaluation), and they may also +share the value of a parameter among all uses of it. But in Basser +Lout, the presence of context-sensitive style information (Section +{@NumberOf style}) forces normal order evaluation and prevents sharing +of parameter values. +@PP +To evaluate an unsized object (pure parse tree), its {@I environment}, +the equivalent of the stack frames in Algol-like languages, must be +available, containing the actual values of all formal parameters +that are visible within the unsized object. Environment handling is +a well-known implementation technique, so it will be discussed +only briefly here. +@PP +Environments are extra subtrees hung from the objects they refer +to. This organization makes excellent use of the ordered dag to +permit environments to be shared, and deleted when the last +reference to them is removed. Several optimizations have been +implemented. Actual parameters known to be invoked only once are moved +in from the environment, not copied; copying could lead to quadratic time +complexity. Actual parameters of the form @Code "@Next" @I object +receive an applicative pre-evaluation which prevents long chains of +@Code "@Next" symbols from forming during the generation of large page +numbers. Some environments which provably contribute nothing are +deleted, most notably when a symbol invocation has no symbols within its +actual parameters and no import list, so that only the environment of its +body need be kept; this saves a great deal of space when objects with +environments are written to auxiliary files (Section {@NumberOf cross}). +@End @SubSection diff --git a/doc/design/s3_9 b/doc/design/s3_9 new file mode 100644 index 0000000..648a1b6 --- /dev/null +++ b/doc/design/s3_9 @@ -0,0 +1,2 @@ +@EndSubSections +@End @Section diff --git a/doc/design/s4_0 b/doc/design/s4_0 new file mode 100644 index 0000000..5f89426 --- /dev/null +++ b/doc/design/s4_0 @@ -0,0 +1,88 @@ +@Section + @Tag { functional } + @Title { Implementation of the functional subset } +@Begin +@PP +The objects and definitions of Lout are very similar to those found in +other functional languages, and they form a natural subset of the +language. So we pause here and present an overview of the Basser Lout +object evaluation algorithm. +@PP +The problem is to take an unsized object (pure parse tree), its +environment (Section {@NumberOf defs.impl}), and its style +(Section {@NumberOf style}), and to produce a PostScript file for +rendering the object on an output device. This file is essentially a +sequence of instructions to print a given string of characters in a +given font at a given point. +@PP +Before the algorithm begins, the parse tree must be obtained, either by +parsing input or by copying from the symbol table. Afterwards the data +structure must be disposed. The algorithm proper consists of five +passes, each a recursive traversal of the structure from the root down +to the leaves and back. +@DP +@I {1. Evaluation of unsized objects.} On the way down, calculate +environments and replace non-recursive, non-receptive symbols by their +bodies (Section {@NumberOf defs.impl}); broadcast fonts to the leaves, +and paragraph breaking and spacing styles to the paragraph nodes. On the +way back up, delete @Eq { FONT }, @Eq { BREAK }, and @Eq { SPACE } nodes, +and insert @Eq { SPLIT }, @Eq { COL }, and @Eq { ROW } nodes +(Section {@NumberOf objects}). +@DP +@I {2. Width calculations and breaking.} Calculate the width of every +subobject from the bottom up. As described in Section {@NumberOf objects}, +@Eq { WIDE } nodes may trigger object breaking sub-traversals during this pass. +@DP +@I {3. Height calculations.} Calculate the height of every subobject, +from the bottom up. +@DP +@I {4. Horizontal coordinates.} Calculate the horizontal coordinate of +each subobject from the top down, and store each leaf's coordinate in +the leaf. +@DP +@I {5. Vertical coordinates and PostScript generation.} Calculate the +vertical coordinate of every subobject from the top down, and at each +leaf, retrieve the character string, font, and horizontal coordinate, +and print the PostScript instruction for rendering that leaf. +@DP +Figure {@NumberOf components} gives the amount of code required for each + +@Figure + @Tag { components } + @Caption { Major components of the Basser Lout interpreter, showing +the approximate number of lines of C code. } +@Begin +@Tab + vmargin { 0.5vx } + @Fmta { @Col @RR A ! @Col B ! @Col @RR C } + @Fmtb { @Col @RR A ! @Col B ! @Col C } +{ + @Rowa A { 1. } B { Initialization } C { 200 } + @Rowa A { 2. } B { Memory allocation, ordered dag operations } C { 400 } + @Rowa A { 3. } B { Lexical analysis, macros, file handling } C { 1,350 } + @Rowa A { 4. } B { Parsing of objects and definitions } C { 1,150 } + @Rowa A { 5. } B { Symbol table and call graph } C { 600 } + @Rowa A { 6. } B { Evaluation of pure parse trees } C { 1,650 } + @Rowa A { 7. } B { Reading, storing, and scaling of fonts } C { 600 } + @Rowa A { 8. } B { Cross references and databases } C { 1,000 } + @Rowa A { 9. } B { Width and height calculations, and breaking } C { 700 } + @Rowa A { 10. } B { @I Constrained and @I AdjustSize } C { 700 } + @Rowa A { 11. } B { Transfer of sized objects into galley tree } C { 450 } + @Rowa A { 12. } B { Galley flushing algorithm } C { 1,500 } + @Rowa A { 13. } B { Coordinate calculations and PostScript output } C { 700 } + @Rowa A { 14. } B { Debugging and error handling } C { 1,200 } + @Rowb vmargin { 0.1c } C { @Line } + @Rowa C { 12,200 } +} +@End @Figure + +pass. Symmetry between horizontal and vertical is exploited throughout +Basser Lout, and passes 2 and 3, as well as 4 and 5, are executed on +shared code. +@PP +The author can see no simple way to reduce the number of passes. The +introduction of horizontal galleys (Section {@NumberOf horizontal}) +would remove the need for the object breaking transformations within this +algorithm that are the principal obstacles in the way of the merging of +passes 2 and 3. +@End @Section diff --git a/doc/design/s5_0 b/doc/design/s5_0 new file mode 100644 index 0000000..d176f77 --- /dev/null +++ b/doc/design/s5_0 @@ -0,0 +1,11 @@ +@Section + @Title { Galleys } +@Begin +@PP +With objects and definitions under control, the author faced the problem +of getting body text, footnotes, floating figures and tables, +references, index entries, and entries in the table of contents into +their places. The resulting investigation occupied three months of +full-time design work, and proceeded approximately as described in +Section {@NumberOf galleys}; the implementation occupied the years 1987-89. +@BeginSubSections diff --git a/doc/design/s5_1 b/doc/design/s5_1 new file mode 100644 index 0000000..ab65bb9 --- /dev/null +++ b/doc/design/s5_1 @@ -0,0 +1,123 @@ +@SubSection + @Tag { galleys } + @Title { The galley abstraction } +@Begin +@PP +Let us take the footnote as a representative example. At some point in +the document, we wish to write +@ID @OneRow @Code { +"preceding text" +"@FootNote { footnote text }" +"following text" +} +and we expect the formatter to remove the footnote from this context and +place it at the bottom of the current page, possibly splitting some or +all of it onto a following page if space is insufficient. +@PP +An object appears in the final document at the point it is invoked, but +this basic property does not hold for footnotes: the point of +invocation and the point of appearance are different. In some way, the +footnote is attached to the document at both points, introducing a cross +linking (Section {@NumberOf genesis}) that cannot be described in purely +functional terms. +@PP +Since the interpretation of any object depends on an environment and +style inherited from the context, the first question must be whether +the footnote inherits them through the invocation point or through +the point(s) of appearance. +@PP +If symbols are to be interpreted statically as heretofore, then environments +must be inherited through the invocation point alone. Dynamic inheritance +through the point of appearance is enticing in some ways: it might +replace the body parameter, and it might help with automatic numbering, +since the number of a footnote is known only at the point of appearance; +but the implementation problems are severe, and static inheritance seems +much simpler and more comprehensible to the user. Style, at least its +available width and height part, must of necessity be inherited through +the point of appearance. For consistency, the entire style should be +inherited in this way. There is a suggestive analogy here with actual +parameters, which have a point of invocation from which they inherit an +environment, and a point of appearance within the body of the enclosing +definition, from which they inherit a style. It may be possible to treat +a footnote as the actual parameter of some symbol, therefore, although +the details seem very obscure. +@PP +But the most profound consequence of having two types of attachment +point is that it leads to two distinctive tree structures. Considering +invocation points only leads to static trees like this one: +@ID @I @Fig margin { 0.3c } { @Tree { +@Node @Ellipse { body text } +@LeftSub { @Node @Ellipse footnote } +@RightSub { + @Node @Ellipse figure + @FirstSub { @Node @Ellipse footnote } +} +}} +which shows that the body text contains a footnote and a figure, the +latter itself containing a footnote. Considering points of appearance +only gives a completely different, dynamic tree: +@ID @I @Fig margin { 0.3c } { @Tree { +@Node @Ellipse { sequence of pages } +@FirstSub { @Node @Ellipse { body text } } +@NextSub { @Node @Ellipse { footnote } } +@NextSub { @Node @Ellipse { figure } } +@NextSub { @Node @Ellipse { footnote } } +}} +The tree can be deeper, for example with sections appearing within +chapters which appear within the body text, which appears within the +final sequence of pages. Document formatting languages generally shirk +the issues raised by this dual tree structure, by making the dynamic +tree built-in, by limiting one or both trees to two levels, and so on, +providing a classic example of the impoverishing effect of failing to +permit language features to attain their natural level of generality. +@PP +We are thus led to propose a second abstraction for document formatting, +which we name the @I galley in recognition of its similarity to the +galleys used in manual typesetting. A galley consists of an object (such +as a footnote) together with a sequence of places where that object may +appear (such as the bottoms of the current and following pages). Splitting +occurs quite naturally when space at any place is insufficient to hold +the entire object. +@PP +In Lout, a footnote galley and its place of appearance are defined +as follows: +@ID @OneRow @Code { +"def @FootPlace { @Galley }" +"" +"def @FootNote into { @FootPlace&&following }" +" right x" +"{ x }" +} +The @Code "@FootPlace" symbol contains the special symbol {@Code "@Galley"}, +indicating that it is a point of appearance for a galley. By placing +invocations of @Code "@FootPlace" at the bottoms of pages, as in Section +{@NumberOf recursion}, we define the desired points of appearance for +footnotes. Symbols whose body contains @Code "@Galley" either directly +or indirectly are called receptive symbols, meaning receptive to +galleys, and they are expanded only on demand. The effect of the +@Code "into" clause is to make each invocation of @Code "@FootNote" a +galley whose object is the result of the invocation in the usual way, +and whose sequence of points of appearance is specified by the @Code "into" +clause; in this example, the sequence of all @Code "@FootPlace" symbols +following the invocation point. +@PP +Lout permits galleys to be invoked within other galleys to arbitrary +depth, so that one may have footnotes within figures within the body +text galley, for example, creating arbitrary static trees. Receptive +symbols like @Code "@FootPlace" may appear within any galley, creating +arbitrary dynamic trees as well. The root of the dynamic tree, which +would normally consist of the sequence of pages of the complete assembled +document, is considered to be a galley whose point of appearance is the +output file. Points of appearance may be @Code preceding or @Code following +the invocation point; entries in tables of contents are the main users +of {@Code preceding}. +@PP +The galley abstraction is adequate for all of the applications listed at +the beginning of this section, except that there is no provision for +sorting index entries and references. Sorting of galleys has been added +to Lout as a built-in feature, invoked by adding a special @Code "@Key" +parameter to the galleys, and using its value as the sort key. The author +was at a loss to find any other way, or any useful generalization of this +feature. Its implementation will be discussed in Section +{@NumberOf cross.impl}. +@End @SubSection diff --git a/doc/design/s5_2 b/doc/design/s5_2 new file mode 100644 index 0000000..a81630d --- /dev/null +++ b/doc/design/s5_2 @@ -0,0 +1,372 @@ +@SubSection + @Tag { flushing } + @Title { The galley flushing algorithm } +@Begin +@PP +Galley components are promoted one by one into the point of appearance in +the dynamic parent galley, then carried along with it, ultimately to the +root galley and the output file. This process is called @I galley +{@I flushing}: the galleys are rivers running together to the sea, and +each component is a drop of water. +@PP +Here is a snapshot of a small dynamic tree, based on the @Code "@PageList" +definitions of Section {@NumberOf recursion}: +@ID @Fig { + +@I 10p @Font { output file } A:: @Box linestyle { noline } margin { 0c } + +||2c + +{ +@I 10p @Font { root galley } +//0.2c +B:: @Box margin { 0c } linestyle { noline } +// +@LittlePage { +|0.5rt - 1 - +//1.2vx &2m A small +//1.2vx @Code "@Galley" * C:: @Box margin { 0.01c } linestyle { noline } +//1rt @Code "@FootSect" +} +// +@Box margin { 0.3c } 2.8c @Wide 8p @Font @Code "@PageList 2" +} + +||2c + +{ +//0.9c @I 10p @Font { body text } +//0.2c D:: @Box margin { 0.3c } 2.8c @Wide 8p @Font paragraph +// @Box margin { 0.3c } 2.8c @Wide 8p @Font { of text. } +// @Box margin { 0.3c } 2.8c @Wide @Code 8p @Font "@Input" +} + +// @Arrow from { B@W } to { A@E } +// @Arrow from { D@W } to { C@E } + +} +The components of the body text galley are lines, except for the special +receptive symbol @Code "@Input" which is a placeholder for as yet unread +input (Section {@NumberOf lookahead}). The components of the root galley are +pages, except for the concluding unexpanded invocation of {@Code "@PageList"}, +which is an inexhaustible source of more pages, expanded on demand. +@PP +The concrete data structure used by Basser Lout permits the galley +flushing algorithm to navigate the dynamic tree and find significant +features quickly: +@ID 10p @Font @Fig maxlabels { 100 } { + +A:: @Ellipse @I { HEAD } + +||1.5c + +@OneCol @OneRow { +B:: @Ellipse @I { RECEIVING * } +// @Arrow from { A@CTR ++ {A@CTR @Angle B@W A@CIRCUM} } to { B@W } +//0.6c +C:: @Ellipse @I { RECEPTIVE } +// @Arrow from { A@CTR ++ {A@CTR @Angle C@W A@CIRCUM} } to { C@W } +//0.6c +D:: @Box margin { 0c } linestyle { noline } +// @Arrow from { A@CTR ++ {A@CTR @Angle D@NW A@CIRCUM} } to { D@NW } +// +@LittlePage { +|0.5rt - 1 - +//1.2vx &2m A small +//1.2vx E:: @Box margin { 0c } linestyle { noline } @Code "@Galley " +//1rt F:: @Box margin { 0c } linestyle { noline } @Code "@FootSect " +} +// @FunnyArrow arrow { forward } from { B@E } to { E@E } +// @FunnyArrow arrow { forward } from { C@E } to { F@E } +//0.6c +C:: @Ellipse @I { GAP } +// @Arrow from { A@CTR ++ {A@CTR @Angle C@W A@CIRCUM} } to { C@W } +//0.6c +C:: @Ellipse @I { RECEPTIVE } +// @Arrow from { A@CTR ++ {A@CTR @Angle C@W A@CIRCUM} } to { C@W } +//0.6c +D:: @Box margin { 0.3c } 2.8c @Wide 8p @Font @Code "@PageList 2" +// @Arrow from { A@CTR ++ {A@CTR @Angle D@NW A@CIRCUM} } to { D@NW } +// @FunnyArrow from { C@E } to { D@W ++ { 1.8 cm 0 } } +} + +||1.0c + +A:: @Ellipse @I { HEAD } +& @Arrow from { B@E } to { A@W } + +||1.5c + +@OneCol @OneRow { +B:: @Box margin { 0.3c } 2.8c @Wide 8p @Font paragraph +// @Arrow from { A@CTR ++ {A@CTR @Angle B@W A@CIRCUM} } to { B@W } +//0.6c +B:: @Ellipse @I { GAP } +// @Arrow from { A@CTR ++ {A@CTR @Angle B@W A@CIRCUM} } to { B@W } +//0.6c +B:: @Box margin { 0.3c } 2.8c @Wide 8p @Font { of text. } +// @Arrow from { A@CTR ++ {A@CTR @Angle B@NW A@CIRCUM} } to { B@NW } +//0.6c +B:: @Ellipse @I { GAP } +// @Arrow from { A@CTR ++ {A@CTR @Angle B@W A@CIRCUM} } to { B@W } +//0.6c +B:: @Ellipse @I { RECEPTIVE } +// @Arrow from { A@CTR ++ {A@CTR @Angle B@W A@CIRCUM} } to { B@W } +//0.6c +C:: @Box margin { 0.3c } 2.8c @Wide 8p @Font @Code "@Input" +// @Arrow from { A@CTR ++ {A@CTR @Angle C@NW A@CIRCUM} } to { C@NW } +// @FunnyArrow from { B@E } to { C@W ++ { 1.2 cm 0 } } +} + +} +Each galley has a @Eq { HEAD } node whose children are its component +objects, separated by @Eq { GAP } nodes recording the inter-component +gaps. +@PP +Each component is preceded by zero or more @I {galley index nodes} of +various types. Every receptive symbol has a @Eq { RECEPTIVE } index pointing +to it, so that it can be found without searching through its +component. If the symbol is currently the target of a galley, it has a +@Eq { RECEIVING } index instead which is also linked to the incoming +galley. Galleys that are currently without a target are linked to the +dynamic tree by @Eq { UNATTACHED } galley indexes, either just after their +most recent target if there has been one, or else at their point of +invocation. +@PP +Each galley should be thought of as a concurrent process, although the +implementation in C uses coroutines implemented by procedures. A galley +may promote its first component only if it has a target, sufficient space +is available at the target to receive the component, and the component +contains no receptive symbols. This last condition seems to be the key +to galley synchronization: it forces a bottom-up promotion regime, +preventing pages from flushing to output before text flushes into them, +for example. +@PP +Each galley contains a number of binary semaphores, shown as asterisks +in our snapshots when set. At any given moment, a galley process is +either running or else is suspended on one of its own semaphores. The +@Eq { HEAD } node contains a semaphore which is set when the galley has tried +to find a target and failed. Each receptive symbol has a semaphore +which is set when that symbol is preventing the first component from +being promoted. +@PP +For example, in the snapshot at the beginning of this section, the root +galley is suspended on the @Code "@Galley" symbol, but the text galley +is running. It will suspend on the @Code "@Input" symbol after the +first two components are promoted. +@PP +Every galley {@I G}, be it a list of pages, body text, a footnote, or +whatever, executes the following algorithm in parallel with every other +galley: +@DP +1. Initially @I G is unattached. Search forwards or backwards from its +@Eq { UNATTACHED } index as required, to find a receptive symbol @I S which +can expand to reveal a target for {@I G}. +@DP +2. If no @I S can be found, suspend on the attachment semaphore. Resume +later from step 1. +@DP +3. Expand @I S to reveal the target of {@I G}. Preserve {@I S}'s +semaphore by moving it to the first receptive symbol within the +expansion of {@I S}. +@DP +4. Calculate the available width and height at the target, and if +@I G is still a pure parse tree, use the environment attached to @I G +and the style information from the target to evaluate @I G as in +Section {@NumberOf functional}. +@DP +5. Examine the components of @I G one by one. For each component there +are three possibilities: +@PP +@I ACCEPT. If the component fits into the available space, and has +no other problems, then promote it into the target. If this is the +first component promoted into this target, and @I G is a forcing +galley (Section {@NumberOf lookahead}), delete every receptive symbol +preceding the target in the parent galley. If @I G is the root galley, +render the component on the output file and dispose it; +@PP +@I REJECT. If the component is too large for the available space, or a +@Eq { FOLLOWS } index (described below) forbids its promotion into this +target, then detach @I G from the target. If this was the first component +at this target, @I S has been a complete failure, so undo step 3 (Basser +Lout is not able to undo step 4); otherwise delete the target. Return to +step 1 and continue immediately; +@PP +@I SUSPEND. If the component contains a receptive symbol, it cannot be +promoted yet. If this symbol is the target of a galley that was written +to an auxiliary file on a previous run, read in that galley and flush +it. Otherwise suspend on the receptive symbol's semaphore; resume later +from step 4. +@DP +6. Terminate when the galley is empty. +@DP +At various points in this algorithm, receptive symbols (and their +semaphores) are deleted in the dynamic parent galley, possibly +permitting it to resume flushing. When this happens, Basser Lout resumes +the parent immediately after @I G suspends or terminates. Also, +whenever a component is promoted, any child galleys connected to +it by @Eq { UNATTACHED } indexes must be resumed, since these +galleys may be able to find a target now. A good example of this +situation occurs when a line of body text with one or more footnotes +is promoted onto a page. Basser Lout gives priority to such children, +suspending @I G while each is given a chance to flush. +@PP +Basser Lout searches for the first target of @I G only in regions of the +dynamic tree that will clearly precede or follow {@I G}'s invocation +point in the final printed document, whichever is specified in the +@Code into clause; subsequent targets are sought later in the same +galley as the first. An exception to this rule, whose necessity will +be made clear later, is that a first @Code following target will be +sought within a dynamic sibling galley preceding {@I G}'s invocation +point: +@ID 10p @Font @Fig { + +{ +@I { dynamic parent } +//0.2c +@Box 2.8c @Wide 4.5c @High +{ + //0.5c A:: @Box margin { 0c } linestyle { noline } @Code "@XTarget" + //1.0c C:: @Box margin { 0c } linestyle { noline } @Eq { UNATTACHED } + //1.3c @Code "@XTarget" +} +} + +||1.5c + +{ +//0.6c +B:: @Box margin {0c} linestyle {noline} @Code "X into { @XTarget&&following }" +//0.2c +@Box 2.8c @Wide 1.5c @High { //0.8c @Code "@GTarget" } +//1.0c +D:: @Box margin {0c} linestyle {noline} @Code "G into { @GTarget&&following }" +//0.2c +@Box 2.8c @Wide 2.5c @High {} +} + +// @Arrow from { A@E ++ {0.2 cm 0} } to { B@W -- {0.2 cm 0} } +// @Arrow from { C@E ++ {0.2 cm 0} } to { D@W -- {0.2 cm 0} } + +} +Here @I G will find the @Code "@GTarget" target within {@I X}. This is +dangerous, since if the first component of @I G is then promoted via +@I X into the first {@Code "@XTarget"} rather than into the second, +{@I G}'s target will not appear later in the final printed document than +its invocation point, as required by the @Code into clause. +@PP +Accordingly, when such a target is chosen, two special galley indexes +are inserted and linked together: a @Eq { PRECEDES } index at {@I G}'s +invocation point, and a @Eq { FOLLOWS } index at the first component of +{@I G}. The algorithm checks before promoting any @Eq { FOLLOWS } index +that its promotion would not place it earlier than the corresponding +@Eq { PRECEDES } index in the same galley, and rejects the component if +it would. Since @Eq { PRECEDES } and @Eq { FOLLOWS } indexes are rarely used, +this check can be implemented by linear search. +@PP +When two components are separated by {@Code "/"}, as opposed to the more +usual {@Code "//"}, each influences the horizontal position of the +other. Because of this, the @I SUSPEND action is in fact taken if a +receptive symbol occurs in any component separated from the first by +{@Code "/"} operators only. Again, linear search forwards to the first +{@Code "//"} suffices for this check. +@PP +A good illustration of these unusual cases is afforded by the +@Code "@Align" symbols from the standard DocumentLayout package. These +are used to produce displayed equations, aligned on their equals signs +despite being separated by arbitrary body text. +@PP +The @Code "@Align" symbols are packaged neatly for the convenience of +the non-expert user, but we will show just the essence of the +implementation here. First, an @Code "@AlignList" galley is created +which contains an infinite supply of @Code "@AlignPlace" receptive +symbols separated by @Code "/" operators: +@ID @Fig { + +{ +@I { body text galley } +//0.2c +@Box 2.8c @Wide 4.0c @High +{ //1.5c + A:: @Box margin { 0c } linestyle { noline } @Code "@Galley" +} +} + +||1.5c + +{ +//2.4c +B:: @Box margin { 0c } linestyle { noline } @Code "@AlignList" +//0.2c +@Box { + @Code "@AlignPlace" +//1vx @Code "@AlignPlace" +//1vx @Code "..." +//1vx @Code "@EndAlignList" +} + +} + +// @Arrow from { A@E ++ {0.2 cm 0} } to { B@W -- {0.2 cm 0} } +} +Then equations like +@ID @ShowMarks @Eq { f(x) ^= g(x) + 2 } +are created and sent to @Code "@AlignPlace&&following" targets. They +collect in the @Code "@AlignList" galley and are aligned there: +@ID @Fig { + +{ +@I { body text galley } +//0.2c +@Box 2.8c @Wide 4.0c @High +{ //1.5c + A:: @Box margin { 0c } linestyle { noline } @Code "@Galley" +} +} + +||1.5c + +{ +//2.4c +B:: @Box margin { 0c } linestyle { noline } @Code "@AlignList" +//0.2c +@Box { + @Line linestyle { dashed } from { xmark ysize } to { xmark 0 } + { + @Eq { f(x) ^= g(x) + 2 } + /1vx @Eq { f(x) - g(x) ^= 2 } + /1vx @Code "..." + /1vx @Code "@EndAlignList" + } +} + +} + +// @Arrow from { A@E ++ {0.2 cm 0} } to { B@W -- {0.2 cm 0} } +} +The @Code "@AlignList" galley does not flush, because its first +component is connected to a receptive symbol by @Code "/" operators. +@PP +After the last equation, an empty forcing galley is sent to +{@Code "@EndAlignList"}, deleting the two remaining receptive symbols from +the @Code "@AlignList" galley and permitting it to flush. @Eq { FOLLOWS } +indexes ensure that each equation finds a target placed in the body text +just after its point of invocation, so the equations return, aligned, to +approximately the points where they were invoked. Notice that the flushing +of body text is suspended until the list of equations is completed, as it +must be, since the horizontal position of the first equation cannot +be known until the last equation is added to the list. +@PP +Layout quality can occasionally be improved by rejecting a component +that could be promoted -- for example, a component of body text that +carries a footnote too large to fit on the current page. Since Lout +does not specify how breaking decisions are made, beyond the basic +constraints imposed by available space and @Code into clauses, in +principle such high quality breaking could be added to the +implementation with no change to the language. However, the +generality of the galley flushing algorithm, and its already +considerable complexity, make this a daunting problem in practice, +although a fascinating one. @TeX [9], with its unnested +set of `floating insertions' clearly identifiable as each page is begun, +has the advantage in this respect. +@End @SubSection diff --git a/doc/design/s5_3 b/doc/design/s5_3 new file mode 100644 index 0000000..3ff9881 --- /dev/null +++ b/doc/design/s5_3 @@ -0,0 +1,125 @@ +@SubSection + @Tag { constraints } + @Title { Size constraints and size adjustments } +@Begin +@PP +The galley flushing algorithm needs to know the available width and +height at each receptive symbol. These symbols may lie within +arbitrarily complex objects, and they may compete with each other for +available space (as body text and footnote targets do), so this +information must be extracted from the tree structure when required. +@PP +For example, consider the object +@ID @Code "5i @Wide { a / b }" +and suppose that the width of @Code { a } is @Eq { 1i, 2i } (@Eq {1i} to +the left of the mark, @Eq { 2i } to the right). What then is the +available width at {@Code { b }}? If we let the width of @Code b be +@Eq {l,r}, we must have +@ID @Eq { (1i up l) + (2i up r) <= 5i } +with the @Eq {non up } (i.e. max) operations arising from mark +alignment. Eliminating them gives +@ID @OneRow @Eq { +matrix { + { 1i + 2i ^<= 5i } +mabove { l + 2i ^<= 5i } +mabove { 1i + r ^<= 5i } +mabove { l + r ^<= 5i } +} +} +and since we assume that @Code a fits into the available space, the +first inequality may be dropped, leaving +@ID @OneRow @Eq { +matrix { + { l ^<= 3i } +mabove { l + r ^<= 5i } +mabove { r ^<= 4i } +} +} +Object @Code b may have width @Eq {l, r} for any @Eq { l } and +@Eq { r } satisfying these inequalities, and no others. +@PP +Here is another example: +@ID @Code "5i @High { a /2ix b }" +Assuming that @Code a has height @Eq {1i,1i}, the height @Eq {l, r} of +@Code b must satisfy +@ID @Eq { 1i + ((1i + l) up 2i) + r <= 5i } +This time the @Eq { non up } operation arises from the mark-to-mark gap +mode, which will widen the @Eq { 2i } gap if necessary to prevent +@Code a and @Code b from overlapping. This inequality can be rewritten as +@ID @OneRow @Eq { +matrix { + { l ^<= infinity } +mabove { l + r ^<= 3i } +mabove { r ^<= 2i } +} +} +In general, Lout is designed so that the available width or height at +any point can be expressed by three inequalities of the form +@ID @OneRow @Eq { +matrix { + { l ^<= x } +mabove { l + r ^<= y } +mabove { r ^<= z } +} +} +where @Eq {x }, @Eq {y} and @Eq {z} may be @Eq { infinity }. We +abbreviate these three inequalities to @Eq { l, r <= x, y, z }, and we +call @Eq {x, y, z} a {@I{size constraint}}. +@PP +The two examples above showed how to propagate the size constraint +@Eq { infinity, 5i, infinity } for +@Code "a / b" down one level to the child {@Code b}. Basser Lout +contains a complete set of general rules for all node types, too +complicated to give here. Instead, we give just one example of how +these rules are derived, using the object +@ID @OneRow { +@Eq {x sub 1} @Code "/" @Eq {x sub 2} @Code "/" @Eq {ldots} @Code +"/" @Eq {x sub n} +} +where @Eq { x sub j } has width @Eq { l sub j , r sub j } for all @Eq {j}. +@PP +Suppose the whole object has width constraint @OneCol @Eq {X,Y,Z}, and we +require the width constraint of {@Eq { x sub i }}. Let +@Eq { L = max sub j ` l sub j } and @Eq { R = max sub j ` r sub j }, +so that @OneCol @Eq {L, R} is the width of the whole object. We assume +@Eq {L, R <= X,Y,Z}. Then @Eq { x sub i } can be enlarged to any size +@Eq { l sub i ` , r sub i } satisfying +@ID @Eq { ( l sub i up L), ( r sub i up R) <= X, Y, Z } +which expands to eight inequalities: +@ID @OneRow @Eq { +matrix { + { l sub i ^<= X } +mabove { L ^<= X } +mabove { l sub i + r sub i ^<= Y } +mabove { l sub i + R ^<= Y } +mabove { L + r sub i ^<= Y } +mabove { L + R ^<= Y } +mabove { r sub i ^<= Z } +mabove { R ^<= Z } +} +} +Three are already known, and slightly rearranging the others gives +@ID @OneRow @Eq { +matrix { + { l sub i ^<= X } +mabove { l sub i ^<= Y - R } +mabove { l sub i + r sub i ^<= Y } +mabove { r sub i ^<= Z } +mabove { r sub i ^<= Y - L } +} +} +Therefore the width constraint of @Eq { x sub i } is +@ID @Eq { min(X, Y-R), Y, min(Z, Y-L) } +The size constraint of any node can be found by climbing the tree to a +@I WIDE or @I HIGH node where the constraint is trivial, then propagating +it back down to the node, and this is the function of procedure +{@I Constrained} in Basser Lout. +@PP +After some components have been promoted into a target, the sizes stored +in its parent and higher ancestors must be adjusted to reflect the +increased size. This is done by yet another set of recursive rules, +upward-moving this time, which cease as soon as some ancestor's size +does not change. These rules are embodied in procedure @I AdjustSize +of Basser Lout. The adjustment must be done before relinquishing +control to any other galley, but not after every component. +@End @SubSection diff --git a/doc/design/s5_4 b/doc/design/s5_4 new file mode 100644 index 0000000..b91d7ce --- /dev/null +++ b/doc/design/s5_4 @@ -0,0 +1,97 @@ +@SubSection + @Tag { lookahead } + @Title { The limited lookahead problem } +@Begin +@PP +Basser Lout assumes that there will be enough internal memory to hold +the symbol table plus a few pages, but not an entire document. This +section describes the consequent problems and how they were solved. +Other interpreters, notably interactive editors running on virtual +memory systems, would not necessarily need this assumption. +@PP +Although Basser Lout can read and format any legal input, its memory +consumption will be optimized when the bulk of the document resides in +galleys whose targets can be identified at the moment they are +encountered. Let us take the typical example of a root galley which +is a list of pages, a @Code "@BodyText" galley targeted into the +pages, @Code "@Chapter" galleys targeted into {@Code "@BodyText"}, +and @Code "@Section" galleys targeted into the @Code "@Chapter" +galleys: +@ID @OneRow @Code { +"@PageList" +"//" +"@BodyText" +"//" +"@Chapter {" +" @Section { ... }" +" @Section { ... }" +" ..." +" @Section { ... }" +"}" +"@Chapter {" +" ..." +"}" +} +Basser Lout is able to read and process such galleys one paragraph at +a time (strictly, from one @Code "//" at the outer level of a galley +to the next), as we now describe. +@PP +When the parser encounters the beginning of a galley, like @Code "@Chapter" +or {@Code "@Section"}, it initiates a new galley process. The special +receptive symbol @Code "@Input" is substituted for the as yet +unread right parameter of the galley. As each paragraph of the right +parameter is read, it is deleted from the parse tree and injected into +the galley's {@Code "@Input"}. The galley is then resumed. The parser +thus acts as an extra +concurrent process; it has low priority, so that input is read only when +there is nothing else to do. Since galleys may be nested, a stack of +@Code "@Input" symbols is needed, each with its own environment and +style. If a galley is encountered for which a target is not immediately +identifiable (a footnote, for example), it is read in its entirety and +hung in pure parse tree form from an @I UNATTACHED index in the usual way, +with an environment but without a style. It will be flushed later +when its component is promoted. +@PP +In addition to producing a steady flow of components from input, we must +also ensure that receptive symbols do not unduly block their +promotion. The @Code "@FootSect" symbol at the foot of each page is a +typical example: until it is deleted the page cannot be printed. +@PP +Receptive symbols are expanded only on demand, so @Code "@FootSect" can +be deleted as soon as we can prove that it is not wanted. The symbol +table can tell us that only @Code "@FootNote" galleys (with +@Code "@FootPlace&&following" targets) want it, so it might be possible +to deduce that @Code "@FootSect" may be deleted as soon as body text +enters the following page. +@PP +The author was unable to make this work, so Basser Lout requires the +user to identify those galleys which will carry the bulk of the document +({@Code "@Chapter"}, {@Code "@Section"}, {@Code "@BodyText"}) as +{@I {forcing galleys}}, by writing @Code "force into" instead of +@Code "into" in their definitions. As described in the previous +section, when a forcing galley attaches to a target, all receptive +symbols preceding the target in its galley are deleted, removing all +impediments to flushing. For example, when a forcing body text galley +enters a new page, the @Code "@FootSect" symbol on the preceding page +will be deleted. It seems likely that a system which could afford to +wait until all input was read before deleting any receptive symbols +would not need forcing galleys. +@PP +Galleys whose targets are a long way from their invocation points can be +a problem. If the direction is {@Code "following"}, such galleys are +held in internal memory for a long time, unless they are to be +sorted. If the direction is +{@Code "preceding"}, then either the entire intervening document must be +held in memory (prevented by the target from flushing), or else some +forcing galley prematurely deletes the target, leaving the galley bereft. +@PP +The typical example of the latter case occurs when the galley is an +entry in the table of contents, launched backwards from the beginning of +a chapter or section. Its target in the table of contents will have +been deleted long before, to permit the rest of the document to print, +so the galley ultimately emerges as an unattached galley promoted out of +the root galley. All such galleys are written to an auxiliary file, +indexed by the missing target. On the next run, just before that target +is deleted, the auxiliary file is checked and any galleys for it are +read in and flushed. +@End @SubSection diff --git a/doc/design/s5_5 b/doc/design/s5_5 new file mode 100644 index 0000000..af4d88b --- /dev/null +++ b/doc/design/s5_5 @@ -0,0 +1,109 @@ +@SubSection + @Tag { horizontal } + @Title { Horizontal galleys } +@Begin +@PP +There is a strong analogy between breaking a column of text into +page-sized pieces, and breaking a paragraph into line-sized pieces. In +fact, the two differ only in direction: vertical for body text, +horizontal for paragraphs. In this section we define {@I{horizontal +galleys}}, and show how they provide an unlimited number of paragraph +breaking styles, as well as solve some other problems. Regrettably, +lack of time has prevented their incorporation into the Basser Lout +interpreter. +@PP +Imagine a galley whose components are separated by horizontal +concatenation operators instead of vertical ones, perhaps indicated by a +@Code { horizontally into } clause. Then all object breaking, including +paragraph breaking, could be replaced by galley component promotion like +this: +@ID @OneRow @Code { +"def @Paragraph right x" +"{" +" def @LinePlace { @Galley }" +"" +" def @LineList" +" {" +" @HExpand @LinePlace" +" //1vx @LineList" +" }" +"" +" def @Par horizontally into { @LinePlace&&preceding }" +" right x" +" { x }" +"" +" @LineList // @Par { 0.2i @Wide {} &0i x &1rt }" +"}" +} +The @Code "@HExpand" operator, which is a primitive of Basser Lout, +horizontally expands the gaps in its right parameter until the result +fills the available space, thus implementing line adjustment, except +when the parameter contains tabulation gaps like {@Code "&1rt"}, which +cause the parameter to be already expanded. The result of +@ID @Code "@Paragraph { A short paragraph of text. }" +would then be something like +@ID 1.5i @Wide { +0.2i @Wide {} & A short paragraph of text. +} +depending on the available horizontal space. An unlimited range of +paragraph breaking styles could be defined, including ragged right, ragged +left, break-and-center, and so on. +@PP +In Basser Lout, indented paragraphs are produced by preceding them with +a horizontal concatenation operator, for example {@Code "|0.5i"}. This +has the unfortunate effect of making an indented paragraph into a single +component of the enclosing galley, so that it will always be kept +together on one page. Horizontal galleys solve this problem with a +simple change to {@Code "@LineList"}: +@ID @OneRow @Code { +"def @LineList" +"{" +" |0.5i @HExpand @LinePlace" +" //1vx @LineList" +"}" +} +showing the flexibility that comes from bringing the full power of the +Lout language to bear on paragraph layout. It is easy to make provision +for a tag on the first line. +@PP +Although Basser Lout permits receptive symbols within paragraphs, they +are of little use, because their available width is calculated after +paragraph breaking, and the incoming galley cannot spread over more than +one line. With horizontal galleys, such symbols would have infinite +available width, and we could easily produce a filled paragraph of +footnotes like this: +@ID 3.5i @Wide { +@OneRow { -2p @Font 1 ^/0.3vo } & See Jones and Saunders (1982). &2m +@OneRow { -2p @Font 2 ^/0.3vo } & Or so Jacobsen (1973) asserts. &2m +@OneRow { -2p @Font 3 ^/0.3vo } & {@I ibid}, p. 327. +} +based on an infinite horizontal sequence of @Code "@FootPlace" symbols +inside a horizontal galley. +@PP +When body text is placed on pages, the length of each column varies +depending on the available vertical space. Horizontal galleys could +analogously produce lines of varying length, and so could fill +non-rectangular shapes. +@PP +An important theoretical benefit of horizontal galleys is that they +would permit horizontal and vertical to be treated in a perfectly +symmetrical way, whereas at present paragraph breaking is horizontal +only, and galley breaking is vertical only. This must simplify the +treatment of non-European languages which fill in unusual directions, +although it is not itself sufficient to implement them. +@PP +There are a few minor problems with horizontal galleys. First, the +syntactic overhead of enclosing each paragraph in @Code "@Paragraph { ... }" +or whatever is unacceptable. Permitting user-defined operators to have lower +precedence than the white space between two words might help here. Second, +the built-in paragraph breaker includes hyphenation, and it permits line +breaks in the input to determine line breaks in the output, if +desired. These features must somehow be preserved. Finally, we have +explained how the Basser Lout interpreter assigns equal width to the +wider columns of tables (Section {@NumberOf style}). The equivalent +situation in vertical galleys occurs when two receptive symbols compete +for vertical space (e.g. @Code "@TextPlace" and {@Code "@FootSect"}), +and there it is conventional to grant as much as required to the first +arrival. It is not clear to the author how these different approaches +can be reconciled. +@End @SubSection diff --git a/doc/design/s5_9 b/doc/design/s5_9 new file mode 100644 index 0000000..648a1b6 --- /dev/null +++ b/doc/design/s5_9 @@ -0,0 +1,2 @@ +@EndSubSections +@End @Section diff --git a/doc/design/s6_0 b/doc/design/s6_0 new file mode 100644 index 0000000..07fb62e --- /dev/null +++ b/doc/design/s6_0 @@ -0,0 +1,18 @@ +@Section + @Title { Cross references } +@Begin +@PP +Cross references, such as `see page 57' and `see Figure 5,' are a useful +but highly error-prone feature of documents. Scribe [7] +introduced a method of keeping them up to date automatically as the +document changes: the user gives each referenced entity a tag, and +operators are provided that return the page or sequence number of the +entity with a given tag. +@PP +A cross reference takes an object (such as a page number) from one point +in the document and copies it to another, and this generalization +suggests other applications. For example, a running header is copied +from the title of a nearby chapter, and a reference is copied from a +bibliographic database. Making the unity of these applications manifest +is an interesting language design problem. +@BeginSubSections diff --git a/doc/design/s6_1 b/doc/design/s6_1 new file mode 100644 index 0000000..0ffc70d --- /dev/null +++ b/doc/design/s6_1 @@ -0,0 +1,85 @@ +@SubSection + @Tag { cross } + @Title { The cross reference abstraction } +@Begin +@PP +In developing the cross reference abstraction, it seemed best to begin +with the database application, since it is the simplest. Database +relations are naturally mapped into Lout definitions: +@ID @OneRow @Code { +"def @Reference" +" named @Tag {}" +" named @Author {}" +" named @Title {}" +" named @Journal {}" +"{}" +} +The set of all invocations of @Code "@Reference" is a relation whose +attributes are the parameters, and whose tuples are the invocations. To +complete the correspondence, we need only declare that the @Code "@Tag" +parameter is special, serving as the key attribute. +@PP +Following the database model, we next need a notation for retrieving the +invocation with a given tag: +@ID @Code "@Reference&&kingston91" +This @I {cross reference} is like an arrow pointing to the invocation. To +access its attributes, we write +@ID @Code "@Reference&&kingston91 @Open { @Author, @Title }" +The @Code "@Open" operator evaluates its right parameter in an +environment which includes the exported parameters of its left. +@PP +An invocation is chosen to be a running header because of its proximity +to the place where it is used, rather than by its tag. Such proximity +is naturally expressed by two special tags, {@Code preceding} and +{@Code following}; for example, @Code "@Sym&&following" will point to +the closest following invocation of @Code "@Sym" in the final printed +document. This is much simpler conceptually than reference to the +internal state of the document formatter at a critical moment, the usual +approach to running headers. +@PP +It turns out that the above design solves all the cross referencing +problems encountered in practice except one, which may be typified by +the problem of finding the number of the page on which the chapter whose +tag is @Code "intro" begins. Two cross referencing steps are needed, +first to {@Code "@Chapter&&intro"}, then from there to +{@Code "@Page&&preceding"}, where the page number is known. +@PP +Given our success so far, this last problem proves to be +surprisingly difficult. We first try +@ID @OneRow @Code { +"@Chapter&&intro @Open {" +" @Page&&preceding @Open { @PageNum }" +"}" +} +but this fails because @Code "@Page&&preceding" is evaluated in the +present context, not in the context of @Code "@Chapter&&intro" as +required. So our next attempt is +@ID @OneRow @Code { +"def @Chapter" +" named @PageNum { @Page&&preceding @Open { @PageNum } }" +" ..." +} +with the @Code "@Page&&preceding" cross reference attached to the +chapter; we write +@ID @Code "@Chapter&&intro @Open { @PageNum }" +This also fails, because parameters are evaluated after substitution, so +once again @Code "@Page&&preceding" is evaluated in the wrong context. We +could of course define a new operator specifically for this case: +@ID @Code "@Page&&{ @Preceding @Chapter&&intro }" +or some such. This is free of the annoying context-sensitivity, but it +seems quite complex, and the expected cross reference @Code "@Page&&preceding" +does not appear. +@PP +The author was lost in these obscurities for some time, and ultimately +rescued himself by looking ahead to the implementation of the +@Code preceding and @Code following tags, to see if a simple extension +of it would solve the problem. This led to the @Code "@Tagged" operator: +@ID @Code "@Page&&preceding @Tagged intro" +placed at the beginning of the body of the chapter will attach @Code intro +as an extra tag to the closest preceding invocation of {@Code "@Page"}, +so that +@ID @Code "@Page&&intro @Open { @PageNum }" +yields the desired page number. There is something low-level and ad hoc +about the @Code "@Tagged" operator, but the two cross references do +appear naturally, and it works. +@End @SubSection diff --git a/doc/design/s6_2 b/doc/design/s6_2 new file mode 100644 index 0000000..2df5478 --- /dev/null +++ b/doc/design/s6_2 @@ -0,0 +1,79 @@ +@SubSection + @Tag { cross.impl } + @Title { Implementation of cross references } +@Begin +@PP +Before an object can be sized and printed, the values of any cross +references within it must be known. If they refer to invocations that +have not yet been read, there is a problem. Scribe [7] +solves it by capitalizing on the fact that documents are formatted +repeatedly during the drafting process. All tagged invocations are +copied to an auxiliary file during the first run, and indexed for quick +retrieval on the second. A new auxiliary file is written during the second +run, for retrieval on the third, and so on. Cross references always lag +one run behind the rest of the document; a perfect copy may be produced +by formatting the same version twice, except in a few pathological cases +that fail to converge. +@PP +Cross referencing in Lout is implemented on top of a simple database +system. Each database is either writable or readable but not both at +once, and holds a set of key-value entries: the keys are @S ASCII +strings, and the values are Lout objects, possibly with environments, +written in Lout source. Operations are provided for writing an entry, +converting from writable to readable, retrieval by key, and sequential +retrieval in key order. +@PP +The implementation, which is quite unsophisticated, employs one or more +@S ASCII {@I{ database files}}, containing the values, and one @S ASCII +{@I{ index file}} per database, containing the keys. To write an entry, +the value is first appended to a database file, then a line like +@ID @Code "@Chapter&&intro ch1.ld 57" +is appended to the index file, giving the file and offset where the value +is stored. To convert from writable to readable, the index file is +sorted. Then retrieval by key requires a binary search of the index +file and one seek into a database file, and sequential retrieval by key +is trivial. +@PP +This database system is used in several ways. For an external database, +say of bibliographic references, the user creates the database file of +values (without environments), Lout creates the index file whenever it +cannot find one, and retrievals by key proceed as usual. Cross +references with tags other than @Code preceding and @Code following are +treated as described above, by writing all tagged invocations (with +environments) to a single database, which is converted to readable at +the end of the run for retrievals on the next run. Sorted galleys, such +as index entries, are written out indexed by target and key and retrieved +sequentially on the next run. Unsorted galleys with preceding targets +which pop off the top of the root galley without finding a target, such +as entries in tables of contents, are treated similarly, except that they +are indexed by target and a sequence number that preserves their relative +order during the sort. +@PP +When Lout processes a multi-file document, one cross reference database +file is written for each input file, but they share a common index +file. At end of run, the new index file is sorted and merged with the +old one in such a way as to preserve entries relating to files not read +on the current run. This provides some support for piecemeal +formatting, but eventually the files must all be formatted together. +@PP +When a @Code preceding or @Code following cross reference is found, +it is attached to a galley index of type @Eq { CROSS_PREC } or +{@Eq { CROSS_FOLL }}, together with an automatically generated tag composed +of the current file name and a sequence number. When a tagged +invocation is found, it is attached to a @Eq { CROSS_TARG } index. These +galley indexes are carried along through the dynamic tree, and +eventually pop off the top of the root galley, at which point it is easy +to determine which cross references refer to which invocations, since +the indexes are now in final printed document order. Each referenced +invocation is then written to the cross reference database, multiply indexed +by the generated tags of the associated cross references. On the next +run, when the same @Code preceding and @Code following cross references +are found, chances are good that the same tags will be generated, and +the appropriate values can be retrieved from the database immediately. +@PP +This approach was the genesis of the @Code "@Tagged" operator, whose +implementation is now immediate: for each @Code "@Tagged" operator we +produce one @Eq { CROSS_PREC } or @Eq { CROSS_FOLL } galley index, +replacing the generated tag with the right parameter of the @Code "@Tagged" +operator. Nothing more is required. +@End @SubSection diff --git a/doc/design/s6_9 b/doc/design/s6_9 new file mode 100644 index 0000000..648a1b6 --- /dev/null +++ b/doc/design/s6_9 @@ -0,0 +1,2 @@ +@EndSubSections +@End @Section diff --git a/doc/design/s7_0 b/doc/design/s7_0 new file mode 100644 index 0000000..2cb4245 --- /dev/null +++ b/doc/design/s7_0 @@ -0,0 +1,84 @@ +@Section + @Title { Conclusion } +@Begin +@PP +Since its public release in October 1991, the Basser Lout interpreter +has been ported without incident to a wide variety of Unix systems and +hardware. It was tested extensively before release on its own +documentation, and the few minor bugs which have emerged since then have +all been fixed in the second release, scheduled to appear in mid-1992. +@PP +Seven substantial packages of definitions are distributed with Basser +Lout. The DocumentLayout package, and its variants ReportLayout and +BookLayout, provide the standard features that all documents +require: pages, columns, paragraphs, headings, footnotes, floating +figures and tables, chapters and sections, displays and lists, access +to bibliographic databases, cross references, and so on +[11]. The BookLayout package has extra features +needed by books, including an automatically generated table of contents, +Roman page numbers for the prefatory material, running page headers, +odd and even page layouts, and a sorted index. The Eq package formats +equations, and Pas formats Pascal programs [10]; Tab +formats tables [12]; and Fig draws figures +[6]. +@PP +The non-expert user who uses these packages perceives a system of a +standard quite similar to other fully developed batch formatters, +although the interface is considerably more coherent than, say, the troff +family's [8]. The expert user perceives a system which +is radically different from previous ones, in which a great deal can be +achieved very quickly. To take an extreme example, Pas was designed, +implemented, tested, and documented in one afternoon. Eq took about +a week, but most of that time was spent in marshalling the vast +repertoire of mathematical symbols, and fine-tuning the spacing. Most +of the effort seems to go into designing a good interface; most symbols +are implemented in just one or a few lines of Lout. +@PP +A group of about 20 satisfied non-expert users has grown up within +the author's department, mainly Honours students with no investment +in older systems to hold them back. Basser Lout has been advertised +on the Internet news as available via anonymous {@I ftp}, so the +extent of its outside user community is hard to gauge. About 50 +people have mailed comments or questions to the author; many +of these people have ported the program, written small definitions, +and modified the standard packages. +@PP +Future work could usefully begin with the improvements suggested in this +paper: overlapping spanning columns, better semantics for available +space, and especially horizontal galleys. Support for non-European +languages is also needed. However, the main task is the development of +an interactive document editor based on Lout. A structure editor similar +to Lilac [13], which already has objects and user-defined +symbols, is envisaged; since cross references are easy when the whole +document is available, the only major new problem is the treatment of +galleys, including the expansion and retraction of receptive symbols. +@LP +@LP +@B { Note. } Since the above was written the author has completed a +revised version of Basser Lout, in which the problem concerning +available space mentioned in Section {@NumberOf style} has been resolved. +@LP +@LP +@B { Acknowledgment. } The author gratefully acknowledges many +valuable discussions with Douglas W. Jones, especially during the +development of the galley abstraction; and also many helpful comments on +presentation by the anonymous referee. +@DP +@DP +@Heading { References } +@NumberedList +@LI @RefPrint kingston91 +@LI @RefPrint kingston91over +@LI @RefPrint kingston91basser +@LI @RefPrint furuta82 +@LI @RefPrint kernighan75 +@LI @RefPrint kingston91fig +@LI @RefPrint reid80 +@LI @RefPrint ossanna76 +@LI @RefPrint knuth84 +@LI @RefPrint kingston91eq +@LI @RefPrint kingston91begin +@LI @RefPrint kingston91tab +@LI @RefPrint brooks91 +@EndList +@End @Section |