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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
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[
#:eval match-eval
@ -85,8 +86,13 @@ variables} that are bound in the result expressions:
(match (hat 23 'bowler)
[(shoe sz col) 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
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
@ -98,10 +104,10 @@ result expression to a list of matches:
#:eval match-eval
(match '(1 1 1)
[(list 1 ...) 'ones]
[else 'other])
[_ 'other])
(match '(1 1 2)
[(list 1 ...) 'ones]
[else 'other])
[_ 'other])
(match '(1 2 3 4)
[(list 1 x ... 4) x])
(match (list (hat 23 'bowler) (hat 22 'pork-pie))