mirror of https://github.com/texmacs/doc.git
73 lines
2.8 KiB
Tcl
73 lines
2.8 KiB
Tcl
<TeXmacs|2.1.2>
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<style|<tuple|tmdoc|english>>
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<\body>
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<tmdoc-title|Macro expansion>
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The main interest of the <TeXmacs>' style-sheet language is the possibility
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to define macros. These come in three flavours: ordinary macros, macros
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which take an arbitrary number of arguments and external macros, whose
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expansion is computed by <name|Scheme> or a plug-in. The macro-related
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primitives are available from the <menu|Source|Macro> menu. Below, we will
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only describe the ordinary macros. For more details, we refer to the
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section about <hlink|macro primitives|../../format/stylesheet/prim-macro.en.tm>.
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Ordinary macros are usually defined using
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<\tm-fragment>
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<inactive*|<assign|my-macro|<macro|<active*|x<rsub|1>>|<active*|<math|\<cdots\>>>|<active*|x<rsub|n>>|body>>>
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</tm-fragment>
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After such an assignment, <markup|my-macro> becomes a new primitive with
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<math|n> arguments, which may be called using
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<\tm-fragment>
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<inactive|<my-macro|<active*|y<rsub|1>>|<active*|<math|\<cdots\>>>|<active*|y<rsub|n>>>>
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</tm-fragment>
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Inside the body of the macro, the <markup|arg> primitive may be used to
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retrieve the values of the arguments to the macro.
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<\tm-fragment>
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<inactive*|<assign|hello|<macro|name|Hello <arg|name>, you look nice
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today!>>>
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</tm-fragment>
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It is possible to call a macro with less or more arguments than the
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expected number. Superfluous arguments are simply ignored. Missing
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arguments take the nullary <markup|uninit> primitive as value:
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<\tm-fragment>
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<inactive*|<assign|hey|<macro|first|second|<style-with|src-compact|none|<if|<equal|<arg|second>|<uninit>>|Hey
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<arg|first>, you look lonely today...|Hey <arg|first> and <arg|second>,
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you form a nice couple!>>>>>
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</tm-fragment>
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We finally notice that you are allowed to compute with macros, in a similar
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way as in functional programming, except that our macros are not closures
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(yet). For instance:
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<\tm-fragment>
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<inactive|<assign|my-macro-copy|<inactive|<value|my-macro>>>>
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</tm-fragment>
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The <markup|compound> tag may be used to apply macros which are the result
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of a computation:
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<\tm-fragment>
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<inactive*|<assign|overloaded-hi|<macro|name|<style-with|src-compact|none|<compound|<if|<nice-weather>|<value|happy-hi>|<value|sad-hi>>|<arg|name>>>>>>
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</tm-fragment>
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<tmdoc-copyright|1998\U2004|Joris van der Hoeven>
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<tmdoc-license|Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version 1.1
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or any later version published by the Free Software Foundation; with no
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Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled "GNU Free
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Documentation License".>
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</body>
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<initial|<\collection>
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</collection>> |