@Section
@Tag { lexical }
@Title { Lexical structure (words, spaces, symbols) and macros }
@Begin
@PP
The input to Lout consists of a sequence of @I {textual units},
textual.unit @Index {Textual unit }
which may be
either {@I{white spaces}},
@I identifiers,
@I delimiters,
or
@I {literal words}. Each
is a sequence of @I characters chosen from:
letter @Index { Letter character }
other @Index { Other character }
quote @Index { Quote character }
escape @Index { Escape character }
comment.char @Index { Comment character }
underscore.char @Index { Underscore character }
@ID @Tab
vmargin { 0.5vx }
@Fmta { @Col A ! @Col B }
{
@Rowa A { letter } B { @Code "@ab-zAB-Z_" }
@Rowa A { white space } B { @I { space formfeed tab newline } }
@Rowa A { quote } B { @Code "\"" }
@Rowa A { escape } B { @Code "\\" }
@Rowa A { comment } B { @Code "#" }
@Rowa A { other } B { @Code "!$%&'()*+,-./0123456789:;<=>?[]^`{|}~" }
}
Notice that @Code "@" and @Code "_" are classed as letters. Basser
Lout accepts the accented letters of the ISO-LATIN-1 character set
(depending on how it is installed), and these are also classed as
letters. The ten digits are classed as `other' characters, and in
fact the `other' class contains all 8-bit characters (except octal 0)
not assigned to previous classes.
@PP
A @I {white space} is a sequence of one or more white space characters.
white.space @Index { White space }
formfeed @Index { Formfeed }
space.f @Index { Space }
Lout treats the formfeed character exactly like the space character;
it is useful for getting page breaks when printing Lout source code.
@PP
A @I delimiter is a sequence of one or more `other' characters which
delimiter @Index { Delimiter }
is the name of a symbol. For example, @Code "{" and @Code "//" are
delimiters. When defining a delimiter, the name must be enclosed
in quotes:
@ID @Code {
"def \"^\" { {} ^& {} }"
}
but quotes are not used when the delimiter is invoked. A delimiter may
have delimiters and any other characters adjacent, whereas identifiers
may not be adjacent to letters or other identifiers. The complete list
of predefined delimiters is
@ID @OneRow @Code {
{
"/"
@JL "//"
@JL "^/"
@JL "^//"
} |2.2cx {
"|"
@JL "||"
@JL "^|"
@JL "^||"
} |2.2cx {
"&"
@JL "^&"
} |2.2cx {
"&&"
@JL "{"
@JL "}"
}
}
A longer delimiter like @Code "<=" will be recognised in
preference to a shorter one like {@Code "<"}.
@PP
An @I identifier is a sequence of one or more letters which is the name of a
identifier @Index { Identifier }
symbol. It is conventional but not essential to begin identifiers with
{@Code "@"}; Basser Lout will print a warning message if it finds an
unquoted literal word (see below) beginning with {@Code "@"}, since such
words are usually misspelt identifiers. The ten digits are not letters
and may not appear in identifiers; and although the underscore character
is a letter and may be used in identifiers, it is not conventional to
do so. The complete list of predefined identifiers is
@ID @OneRow @Code {
{ "@BackEnd"
@JL "@Background"
@JL "@Begin"
@JL "@Break"
@JL "@Case"
@JL "@Common"
@JL "@Char"
@JL "@CurrFace"
@JL "@CurrFamily"
@JL "@CurrLang"
@JL "@Database"
@JL "@End"
@JL "@Enclose"
@JL "@Filter"
@JL "@FilterErr"
@JL "@FilterIn"
@JL "@FilterOut"
@JL "@Font"
@JL "@ForceGalley"
@JL "@Galley"
@JL "@Graphic"
@JL "@HAdjust"
@JL "@HContract"
@JL "@HCover"
@JL "@HExpand"
@JL "@High"
@JL "@HLimited"
@JL "@HScale"
@JL "@HShift"
@JL "@HSpan"
} |4.4cx {
"@Include"
@JL "@IncludeGraphic"
@JL "@Insert"
@JL "@KernShrink"
@JL "@Key"
@JL "@Language"
@JL "@LClos"
@JL "@LEnv"
@JL "@LInput"
@JL "@LVis"
@JL "@LUse"
@JL "@Meld"
@JL "@Merge"
@JL "@Minus"
@JL "@Moment"
@JL "@Next"
@JL "@NotRevealed"
@JL "@Null"
@JL "@OneCol"
@JL "@OneOf"
@JL "@OneRow"
@JL "@Open"
@JL "@Optimize"
@JL "@PAdjust"
@JL "@PageLabel"
@JL "@PlainGraphic"
@JL "@Plus"
@JL "@PrependGraphic"
@JL "@RawVerbatim"
@JL "@Rotate"
} |4.4cx {
"@Rump"
@JL "@Scale"
@JL "@SetColor"
@JL "@SetColour"
@JL "@Space"
@JL "@StartHSpan"
@JL "@StartHVSpan"
@JL "@StartVSpan"
@JL "@SysDatabase"
@JL "@SysInclude"
@JL "@SysIncludeGraphic"
@JL "@SysPrependGraphic"
@JL "@Tag"
@JL "@Tagged"
@JL "@Target"
@JL "@Underline"
@JL "@Use"
@JL "@VAdjust"
@JL "@VContract"
@JL "@VCover"
@JL "@Verbatim"
@JL "@VExpand"
@JL "@VLimited"
@JL "@VScale"
@JL "@VShift"
@JL "@VSpan"
@JL "@Wide"
@JL "@Yield"
@JL "@YUnit"
@JL "@ZUnit"
}
}
plus the names of the parameters of @@Moment. The symbols @@LClos, @@LEnv,
lclos @Index { @@LClos symbol }
lenv @Index { @@LEnv symbol }
linput @Index { @@LInput symbol }
lvis @Index { @@LVis symbol }
luse @Index { @@LUse symbol }
@@LInput, @@LVis and @@LUse appear in cross reference databases generated
by Lout and are not for use elsewhere.
@PP
A sequence of characters which is neither a white space, an identifier, nor a
delimiter, is by default a @I {literal word}, which means that it will
word @Index { Word }
literal.word @Index { Literal word }
quoted.word @Index { Quoted word }
pass through Lout unchanged. An arbitrary sequence of characters
enclosed in double quotes, for example @Code "\"{ }\"", is also a
literal word. Space characters may be included, but not tabs or
newlines. There are special character sequences, used only between
quotes, for obtaining otherwise inaccessible characters:
@ID @Tab
vmargin { 0.5vx }
@Fmta { @Col A ! @Col B }
{
@Rowa A { @Code "\\\"" } B { produces @Code "\"" }
@Rowa A { @Code "\\\\" } B { "\\" }
@Rowa A { @Code "\\ddd" } B { the character whose ASCII code is }
@Rowa A { } B { the up to three digit octal number {@Code ddd} }
}
So, for example, @Code "\"\\\"@PP\\\"\"" produces {@Code "\"@PP\""}.
@PP
When the comment character
comment @Index { Comment }
@Code "#" is encountered, everything from
that point to the end of the line is ignored. This is useful for
including reminders to oneself, like this:
@ID @OneRow @Code {
"# Lout user manual"
"# J. Kingston, June 1989"
}
for temporarily deleting parts of the document, and so on.
@PP
@I Macros
macro @Index { Macro }
provide a means of defining symbols which stand for a
sequence of textual units rather than an object. For example, the macro
definition
@ID @Code {
"macro @PP { //1.3vx 2.0f @Wide &0i }"
}
makes Lout replace the symbol @Code "@PP" by the given textual units
before assembling its input into objects. A similar macro to this
one is used to separate the paragraphs of the present document. The
enclosing braces and any spaces adjacent to them are dropped, which can
be a problem: @Code "@PP2i" has result {@Code "//1.3vx 2.0f @Wide &0i2i"}
which is erroneous.
@PP
The meaning of symbols used within the body of a macro is determined by
where the macro is defined, not by where it is used. Due to implementation
problems, @@Open symbols will not work within macros. Named and body
parameters will work if the symbol that they are parameters of is also
present. There is no way to get a left or right brace into the body of
a macro without the matching brace.
@PP
Macros may be nested within other definitions and exported, but they may
not be parameters. They may not have parameters or nested definitions
of their own, and consequently a preceding @Code export clause (Section
{@NumberOf visibility}) would be pointless; however, an @Code import
clause is permitted.
@End @Section
