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refine note on immutable hash table performance

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svn: r14664
This commit is contained in:
Matthew Flatt 2009-04-29 21:55:16 +00:00
parent f7d8270a6c
commit d5b5c8fb97
1 changed files with 5 additions and 2 deletions
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7
collects/scribblings/reference/hashes.scrbl
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@ -21,8 +21,11 @@ A @deftech{hash table} (or simply @deftech{hash}) maps each of its
keys to a single value. For a given hash table, keys are equivalent keys to a single value. For a given hash table, keys are equivalent
via @scheme[equal?], @scheme[eqv?], or @scheme[eq?], and keys are via @scheme[equal?], @scheme[eqv?], or @scheme[eq?], and keys are
retained either strongly or weakly (see @secref["weakbox"]). A hash retained either strongly or weakly (see @secref["weakbox"]). A hash
table is also either mutable or immutable; immutable tables support table is also either mutable or immutable. Immutable tables support
constant-time functional update. constant-time access and update, just like mutable hash tables; the
the constant on immutable operations is usually larger, but the
functional nature of immutable hash tables can pay off in certain
algorithms.
A hash table can be used as a two-valued @tech{sequence} (see A hash table can be used as a two-valued @tech{sequence} (see
@secref["sequences"]). The keys and values of the hash table serve as @secref["sequences"]). The keys and values of the hash table serve as