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docs: clarification for `immutable?'

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This commit is contained in:
Matthew Flatt 2012-12-30 10:01:58 -06:00
parent ede0e3c625
commit 8b7379a7ad
1 changed files with 8 additions and 0 deletions
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8
collects/scribblings/reference/booleans.scrbl
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@ -115,6 +115,14 @@ Returns @racket[#t] if @racket[v] is an immutable @tech{string},
@tech{byte string}, @tech{vector}, @tech{hash table}, or box,
@racket[#f] otherwise.
Note that @racket[immutable?] is not a general predicate for
immutability (despite its name). It works only for a handful of
datatypes for which a single predicate---@racket[string?],
@racket[vector?], @|etc|---recognizes both mutable and immutable variants
of the datatype. In particular, @racket[immutable?] produces
@racket[#f] for a @tech{pair}, even though pairs are immutable, since
@racket[pair?] implies immutability.
@examples[
(immutable? 'hello)
(immutable? "a string")