mirror of https://github.com/texmacs/doc.git
217 lines
6.9 KiB
Tcl
217 lines
6.9 KiB
Tcl
<TeXmacs|1.0.7.16>
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<style|tmdoc>
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<\body>
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<tmdoc-title|Matching regular expressions>
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Regular expressions naturally generalize from strings to trees and allow to
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test whether a given tree matches a given pattern. <TeXmacs> implements the
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primitives <scm|match?> and <scm|match> for this purpose, which also
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provide support for wildcards, user-defined grammars and more.
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<\explain>
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<scm|(match? <scm-arg|expr> <scm-arg|pattern>)><explain-synopsis|check
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whether a scheme expression satisfies a pattern>
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<|explain>
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This function determines whether a scheme expression <scm-arg|expr>
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satisfies a given <scm-arg|pattern>. It will be detailed below how to
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form valid patterns. The matching routines recursively understand that
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native trees match their scheme counterparts. For instance, <scm|(match?
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(tree "x") "x<name|">)> will return <scm|(())> (meaning <scm|<scm|>#t>
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<with|color|red|-is this as intended?>) and <scm|(match? (tree "x")
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"y<name|">)> will return <scm|#f>.
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</explain>
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<\explain>
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<scm|(match <scm-arg|l> <scm-arg|pattern>
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<scm-arg|bindings>)><explain-synopsis|solutions to a given pattern under
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bindings>
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<|explain>
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Given a list <scm-arg|l> of scheme expressions, a <scm-arg|pattern> with
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free variables and an association list of <scm-arg|bindings>, this
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routine determines all substitutions of free variables by values
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(extending the given <scm-arg|bindings>), for which <scm-arg|l> matches
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the <scm-arg|pattern>.
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<with|color|red|Give an example, please.>
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</explain>
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<\explain>
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<scm|(define-regexp-grammar <scm-args|rules>)><explain-synopsis|user
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defined matching grammars>
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<|explain>
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Given a list of rules of the form <scm|(:<scm-arg|var>
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<scm-arg|pattern-1> ... <scm-arg|pattern-n>)>, this instruction defines a
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new terminal symbol <scm|:<scm-arg|var>> for each such rule, which
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matches the disjunction of the patterns <scm-arg|pattern-1> until
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<scm-arg|pattern-n>. This terminal symbol can then be used as an
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abbreviation in matching patterns. Grammar rules may be interdependent.
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See example below.
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</explain>
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Valid patterns are formed in the following ways:
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<\explain>
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<scm-arg|leaf><explain-synopsis|symbols, strings, etc.>
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<|explain>
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A <scm-arg|leaf> is only matched against itself.
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</explain>
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<\explain>
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<scm|(<scm-arg|pattern-1> ... <scm-arg|pattern-n>)><explain-synopsis|lists>
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<|explain>
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In the case when lists <scm|l-1> until <scm|l-n> match
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<scm-arg|pattern-1> until <scm-arg|pattern-n>, their concatenation
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matches the pattern <scm|(<scm-arg|pattern-1> ... <scm-arg|pattern-n>)>.
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</explain>
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<\explain>
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<scm|:%1>, <scm|:%2>, <scm|:%3> ..., <scm|:*><explain-synopsis|wildcards>
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<|explain>
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The wildcard <scm|:%n>, where <scm|n> is a number matches any list of
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length <scm|n>. The wildcard <scm|:*> matches any list, including the
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empty list.
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</explain>
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<\explain>
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<scm|'<scm-arg|var>><explain-synopsis|variables>
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<|explain>
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This pattern attempts to bind the variable <scm-arg|var> against the
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expression. If <scm-arg|var> is used only once, then it essentially
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behaves as a wildcard. More generally, it can be used to form patterns
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with identical subexpressions. For instance, the pattern <scm|(frac 'x
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'x)> will match all fractions <math|<frac|x|x>>.
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</explain>
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<\explain>
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<scm|:<scm-arg|var>><explain-synopsis|user-provided grammar rules>
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<|explain>
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In the case when <scm|:<scm-arg|var>> is a user-provided terminal symbol
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(see <scm|define-regexp-grammar> above), this pattern matches the
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corresponding grammar.
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</explain>
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<\explain>
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<scm|:<scm-arg|pred?>><explain-synopsis|arbitrary <scheme> predicates>
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<|explain>
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Given a <scheme> predicate <scm-arg|pred?>, such as <scm|string?>, this
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pattern matches any scheme expression which satisfies the predicate.
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</explain>
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<\explain>
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<scm|(:not <scm-arg|pattern>)>
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<scm|(:or <scm-arg|pattern-1> ... <scm-arg|pattern-n>)>
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<scm|(:and <scm-arg|pattern-1> ... <scm-arg|pattern-n>)><explain-synopsis|logical
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operations>
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<|explain>
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Negation, disjunction and conjunction of patterns.
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</explain>
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<\explain>
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<scm|(:repeat <scm-arg|pattern>)><explain-synopsis|repetition>
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<|explain>
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Given lists <scm|l-1> until <scm|l-n> which match <scm-arg|pattern>,
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their concatenation matches the repetition <scm|(:repeat
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<scm-arg|pattern>)>. In particular, the empty list is matched.
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</explain>
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<\explain>
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<scm|(:group <scm-arg|pattern-1> ... <scm-arg|pattern-n>)><explain-synopsis|grouping>
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<|explain>
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Groups a concatenation of patterns into a new list patterns. For
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instance, all lists of the form <scm|(a b a b ... a b)> are matched by
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<scm|(:repeat (:group a b))>, whereas <scm|(:repeat (a b))> rather
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matches all lists of the form <scm|((a b) (a b) ... (a b))>.
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</explain>
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<\explain>
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<scm|(:quote <scm-arg|expr>)><explain-synopsis|quotation>
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<|explain>
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Only matches a given expression <scm-arg|expr>.
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</explain>
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<\example>
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The tree
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<\scm-code>
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(define t '(foo (bar "x") (bar "y") (option "z")))
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</scm-code>
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matches the pattern <scm|(foo (:repeat (bar :%1)) :*)>, but not <scm|(foo
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(:repeat (bar 'x)) :*)>. The call <scm|(match t '(foo 'x 'y :*))> will
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return <scm|(((x . (bar "x")) (y . (bar "y"))))>.
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<\with|color|red>
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Actually this gives ``wrong-number-of-args'' but we have:
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</with>
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<\session|scheme|default>
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<\input|Scheme] >
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(define t '(foo (bar "x") (bar "y") (option "z")))
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</input>
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<\unfolded-io|Scheme] >
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(match? t '(foo 'x 'y :*))
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<|unfolded-io>
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(((y bar "y") (x bar "x")))
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</unfolded-io>
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</session>
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Which has a different format
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</example>
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<\example>
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Consider the grammar
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<\scm-code>
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(define-regexp-grammar
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\ \ (:a a b c)
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\ \ (:b (:repeat :a)))
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</scm-code>
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Then the list <scm|(a b x y c a a)> matches the pattern <scm|(:b :%2
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:b)>.
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<with|color|red|Does it?>
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<\session|scheme|default>
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<\input|Scheme] >
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(define-regexp-grammar
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\ \ (:a a b c)
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\ \ (:b (:repeat :a)))
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</input>
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<\unfolded-io|Scheme] >
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(match? \ '(a b x y c a a) \ (:b :%2 :b))
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<|unfolded-io>
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misc-error
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</unfolded-io>
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<\input|Scheme] >
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\;
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</input>
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</session>
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</example>
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<tmdoc-copyright|2007|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>
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<\collection>
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<associate|language|english>
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</collection>
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</initial> |