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46 lines
2.2 KiB
Racket
46 lines
2.2 KiB
Racket
#lang scribble/manual
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@(require scribble/eval (for-label racket sugar))
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@(define my-eval (make-base-eval))
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@(my-eval `(require sugar))
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@title{Cache}
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@defmodule[#:multi (sugar/cache (submod sugar/cache safe))]
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If, like Ricky Bobby and me, you want to go fast, then try using more caches. They're wicked fast.
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@defproc[
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(make-caching-proc
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[proc procedure?])
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procedure?]
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Make a caching version of @racket[_proc]. This means a hash table will be attached to @racket[_proc], and result values will automatically be saved & retrieved. The arguments to the procedure are used as the hash key.
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In the example below, notice that both invocations of @racketfont{slow-op} take approximately the same time, whereas the second invocation of @racketfont{fast-op} gets its value from the cache, and is thus nearly instantaneous.
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@examples[#:eval my-eval
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(define (slow-op x) (for/sum ([i (in-range 100000000)]) i))
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(time (slow-op 42))
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(time (slow-op 42))
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(define fast-op (make-caching-proc slow-op))
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(time (fast-op 42))
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(time (fast-op 42))
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]
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Keep in mind that the cache is only available to external callers of the resulting function. So if @racket[_proc] calls itself recursively, these calls are @italic{not} accelerated by the cache. If that's the behavior you need, use @racket[define/caching] to create a new recursive function.
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@defform[(define/caching (name arg ... . rest-arg) body ...)]
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Like @racket[define], but automatically uses @racket[make-caching-proc] to define a caching version of the function. If the function is recursive, the cache will be used for the recursive calls.
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In the example below, @racketfont{fib} is a recursive function. Notice that simply wrapping the function in @racket[make-caching-proc] doesn't work in this case, because @racketfont{fib}'s recursive calls to itself bypass the cache. But @racketfont{fib-fast} is rewritten to recur on the caching function, and the caching works as expected.
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@examples[#:eval my-eval
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(define (fib x)
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(if (< x 2) 1 (+ (fib (- x 1)) (fib (- x 2)))))
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(define fibber (make-caching-proc fib))
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(define/caching (fib-fast x)
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(if (< x 2) 1 (+ (fib-fast (- x 1)) (fib-fast (- x 2)))))
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(time (fib 32))
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(time (fibber 32))
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(time (fib-fast 32))
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] |