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doc: Augment "Pattern Matching" section.

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* doc/ref/match.texi (Pattern Matching): Mention records.  Add an
  example showing record matching and the `=' pattern.  Point users to
  `match.upstream.scm'.
This commit is contained in:
Ludovic Courtès 2011-09-03 22:16:54 +02:00
parent 5fcb7b3cc5
commit 8568067836
1 changed files with 40 additions and 6 deletions
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46
doc/ref/match.texi
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@ -1,6 +1,6 @@
@c -*-texinfo-*-
@c This is part of the GNU Guile Reference Manual.
@c Copyright (C) 2010 Free Software Foundation, Inc.
@c Copyright (C) 2010, 2011 Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions.
@c
@ -26,7 +26,7 @@ matcher found in many Scheme implementations.
@cindex pattern variable
A pattern matcher can match an object against several patterns and
extract the elements that make it up. Patterns can represent any Scheme
object: lists, strings, symbols, etc. They can optionally contain
object: lists, strings, symbols, records, etc. They can optionally contain
@dfn{pattern variables}. When a matching pattern is found, an
expression associated with the pattern is evaluated, optionally with all
pattern variables bound to the corresponding elements of the object:
@ -43,8 +43,8 @@ In this example, list @var{l} matches the pattern @code{('hello (who))},
because it is a two-element list whose first element is the symbol
@code{hello} and whose second element is a one-element list. Here
@var{who} is a pattern variable. @code{match}, the pattern matcher,
locally binds @var{who} to the value contained in this one-element list,
i.e., the symbol @code{world}.
locally binds @var{who} to the value contained in this one-element
list---i.e., the symbol @code{world}.
The same object can be matched against a simpler pattern:
@ -112,8 +112,8 @@ pat ::= identifier anything, and binds identifier
| #(pat_1 ... pat_n pat_n+1 ooo) vector of n or more, each element
of remainder must match pat_n+1
| #&pat box
| ($ struct-name pat_1 ... pat_n) a structure
| (= field pat) a field of a structure
| ($ record-name pat_1 ... pat_n) a record
| (= field pat) a ``field'' of an object
| (and pat_1 ... pat_n) if all of pat_1 thru pat_n match
| (or pat_1 ... pat_n) if any of pat_1 thru pat_n match
| (not pat_1 ... pat_n) if all pat_1 thru pat_n don't match
@ -154,6 +154,40 @@ The names @code{quote}, @code{quasiquote}, @code{unquote},
@code{or}, @code{not}, @code{set!}, @code{get!}, @code{...}, and
@code{___} cannot be used as pattern variables.
Here is a more complex example:
@example
(use-modules (srfi srfi-9))
(let ()
(define-record-type person
(make-person name friends)
person?
(name person-name)
(friends person-friends))
(letrec ((alice (make-person "Alice" (delay (list bob))))
(bob (make-person "Bob" (delay (list alice)))))
(match alice
(($ person name (= force (($ person "Bob"))))
(list 'friend-of-bob name))
(_ #f))))
@result{} (friend-of-bob "Alice")
@end example
@noindent
Here the @code{$} pattern is used to match a SRFI-9 record of type
@var{person} containing two or more slots. The value of the first slot
is bound to @var{name}. The @code{=} pattern is used to apply
@code{force} on the second slot, and then checking that the result
matches the given pattern. In other words, the complete pattern matches
any @var{person} whose second slot is a promise that evaluates to a
one-element list containing a @var{person} whose first slot is
@code{"Bob"}.
Please refer to the @code{ice-9/match.upstream.scm} file in your Guile
installation for more details.
Guile also comes with a pattern matcher specifically tailored to SXML
trees, @xref{sxml-match}.