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Describe match scoping behavior more precisely.

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This commit is contained in:
Sam Tobin-Hochstadt 2015-03-11 16:15:17 -04:00
parent 33d653113d
commit 2ccd4b1a95
1 changed files with 7 additions and 4 deletions
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11
pkgs/racket-doc/scribblings/reference/match.scrbl
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@ -22,9 +22,11 @@ on regular-expression matching on strings, bytes, and streams.
Finds the first @racket[pat] that matches the result of Finds the first @racket[pat] that matches the result of
@racket[val-expr], and evaluates the corresponding @racket[body]s with @racket[val-expr], and evaluates the corresponding @racket[body]s with
bindings introduced by @racket[pat] (if any). The last @racket[body] bindings introduced by @racket[pat] (if any). Bindings introduced by
@racket[pat] are not available in other parts of @racket[pat].
The last @racket[body]
in the matching clause is evaluated in tail position with respect to in the matching clause is evaluated in tail position with respect to
the @racket[match] expression. the @racket[match] expression.
To find a match, the @racket[clause]s are tried in order. If no To find a match, the @racket[clause]s are tried in order. If no
@racket[clause] matches, then the @exnraise[exn:misc:match?]. @racket[clause] matches, then the @exnraise[exn:misc:match?].
@ -58,12 +60,13 @@ In more detail, patterns match as follows:
@racketidfont{...}, @racketidfont{.._}, @racketidfont{...}, @racketidfont{.._},
@racketidfont{..}@racket[_k], and @racketidfont{..}@racket[_k], and
@racketidfont{..}@racket[_k] for non-negative integers @racketidfont{..}@racket[_k] for non-negative integers
@racket[_k]) or @racket[(var _id)] --- matches anything, and binds @racket[id] to the @racket[_k]) or @racket[(var _id)] --- matches anything, and binds @racket[_id] to the
matching values. If an @racket[_id] is used multiple times matching values. If an @racket[_id] is used multiple times
within a pattern, the corresponding matches must be the same within a pattern, the corresponding matches must be the same
according to @racket[(match-equality-test)], except that according to @racket[(match-equality-test)], except that
instances of an @racket[_id] in different @racketidfont{or} and instances of an @racket[_id] in different @racketidfont{or} and
@racketidfont{not} sub-patterns are independent. @racketidfont{not} sub-patterns are independent. The binding for @racket[_id] is
not available in other parts of the same pattern.
@examples[ @examples[
#:eval match-eval #:eval match-eval