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[let-regexp] docs

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ben 2016-02-25 12:21:19 -05:00
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scribblings/trivial.scrbl
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@ -84,7 +84,7 @@ In other words, the result is one string for the matched substring and an unknow
(U #f (List String String)))
]
Regular expression patterns are expensive to compile, so we offer a definition form that remembers the number of groups in a pattern for later calls to @racket[regexp-match:].
Large regular expression patterns are expensive to compile, so we offer a definition form that remembers the number of groups in a pattern for later calls to @racket[regexp-match:].
@defform*[((define-regexp: id pattern)
(define-pregexp: id pattern)
@ -110,6 +110,32 @@ Regular expression patterns are expensive to compile, so we offer a definition f
(U #f (List Bytes))))
]
Similarly, @racket[let-regexp:] and friends are expression-binding forms.
For both the @racket[define-] and @racket[let-] forms, the @racket[pattern] may be any expression.
The only difference is that regular expression metadata is checked and preserved if present.
@defform*[((let-regexp: ([id expr] ...) expr ...)
(let-pregexp: ([id expr] ...) expr ...)
(let-byte-regexp: ([id expr] ...) expr ...)
(let-byte-pregexp: ([id expr] ...) expr ...))]{}
@examples[#:eval trivial-eval
(let-regexp: ([hamburger (regexp: "^{{.*beef.*}}$")])
(ann (regexp-match: hamburger "{{ lettuce tomato cheese }}")
(U #f (List String))))
(let-pregexp: ([bigmac (pregexp: "(bun).*(bun).*(bun)")])
(ann (regexp-match: bigmac "bun tomato bun meat bun")
(U #f (List String String String String))))
(let-byte-regexp: ([low-carb (byte-regexp: #"^([^bun]*)meat([^bun]*)$")])
(ann (regexp-match: low-carb "meat meat meat")
(U #f (List Bytes Bytes Bytes))))
(let-byte-pregexp: ([double-diet (byte-pregexp: #" {2}")])
(ann (regexp-match: double-diet " ")
(U #f (List Bytes))))
]
The following expression forms also cache the number of pattern groups.
Use these instead of the standard defaults.