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adjust guide to avoid else for match and to encourage _

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Robby Findler 2013-05-04 21:32:02 -05:00
parent 350e8184eb
commit b6e4bbdbc8
1 changed files with 9 additions and 3 deletions
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12
collects/scribblings/guide/match.scrbl
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@ -72,7 +72,8 @@ constructor:
] ]
Unquoted, non-constructor identifiers in a pattern are @tech{pattern Unquoted, non-constructor identifiers in a pattern are @tech{pattern
variables} that are bound in the result expressions: variables} that are bound in the result expressions, except @racket[_],
which does not bind (and thus is usually used as a catch-all):
@interaction[ @interaction[
#:eval match-eval #:eval match-eval
@ -85,8 +86,13 @@ variables} that are bound in the result expressions:
(match (hat 23 'bowler) (match (hat 23 'bowler)
[(shoe sz col) sz] [(shoe sz col) sz]
[(hat sz stl) sz]) [(hat sz stl) sz])
(match (hat 11 'cowboy)
[(shoe sz 'black) 'a-good-shoe]
[(hat sz 'bowler) 'a-good-hat]
[_ 'something-else])
] ]
An ellipsis, written @litchar{...}, acts like a Kleene star within a An ellipsis, written @litchar{...}, acts like a Kleene star within a
list or vector pattern: the preceding sub-pattern can be used to match list or vector pattern: the preceding sub-pattern can be used to match
any number of times for any number of consecutive elements of the list any number of times for any number of consecutive elements of the list
@ -98,10 +104,10 @@ result expression to a list of matches:
#:eval match-eval #:eval match-eval
(match '(1 1 1) (match '(1 1 1)
[(list 1 ...) 'ones] [(list 1 ...) 'ones]
[else 'other]) [_ 'other])
(match '(1 1 2) (match '(1 1 2)
[(list 1 ...) 'ones] [(list 1 ...) 'ones]
[else 'other]) [_ 'other])
(match '(1 2 3 4) (match '(1 2 3 4)
[(list 1 x ... 4) x]) [(list 1 x ... 4) x])
(match (list (hat 23 'bowler) (hat 22 'pork-pie)) (match (list (hat 23 'bowler) (hat 22 'pork-pie))