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53 lines
1.8 KiB
Plaintext
53 lines
1.8 KiB
Plaintext
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created: 20150220200255000
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modified: 20150221222349000
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tags: [[Macro Syntax]]
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title: Macro Definition Syntax
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type: text/vnd.tiddlywiki
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<<.preamble """What follows is a formal presentation of the syntax of the `\define` pragma, using [[railroad diagrams|Railroad Diagrams]]. A [[simpler overview|Macro Definitions in WikiText]] is also available.""">>
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<$railroad text="""
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"\define" space name params [:space] rest
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"""/>
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<<.place space>> denotes a sequence of [[whitespace characters|Filter Whitespace]].
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The [[macro|Macros]]'s <<.place name>> is a sequence of non-whitespace characters other than `(` or `>`.
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The parameter declaration list (<<.place params>>) has the following syntax:
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<$railroad text="""
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"(" [:sep] [:{ param sep }] ")"
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"""/>
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The parameter separator (<<.place sep>>) is any sequence of characters that does not match a <<.place param-name>>. Among other things, this includes commas, spaces and linefeeds.
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A <<.place param-name>> is a sequence of letters (`A`--`Z`, `a`--`z`), digits (`0`--`9`), hyphens (`-`) and underscores (`_`).
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Each individual <<.place param>> has the following syntax:
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<$railroad text="""
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param-name [: [:space] ":" [:space] default ]
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")"
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"""/>
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The optional <<.place default>> value of a parameter is specified as follows:
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<$railroad text={{$:/editions/tw5.com/railroad/macro-parameter-value}}/>
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The <<.place rest>> of the definition has the following syntax:
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<$railroad text="""
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( snippet | lf snippet lf "\end" [:space] ) lf
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"""/>
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<<.place lf>> denotes a linefeed.
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The <<.place snippet>> is any sequence of characters that doesn't terminate the macro definition. That is to say, a single-line snippet cannot contain a linefeed, and a multi-line snippet cannot contain `\end` on a line of its own.
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The snippet can contain placeholders with the following syntax:
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<$railroad text="""
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( "$" name "$" | "$" "(" name ")" "$" )
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"""/>
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