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updated docs for struct-type-contract/c

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This commit is contained in:
Ryan Culpepper 2011-07-11 15:35:04 -06:00
parent 59a85b3eb2
commit 5a10ef7550
1 changed files with 42 additions and 19 deletions
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61
collects/unstable/scribblings/prop-contract.scrbl
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@ -16,34 +16,57 @@
Produces a contract for struct type properties. When the contract is Produces a contract for struct type properties. When the contract is
applied to a struct type property, it produces a wrapped struct type applied to a struct type property, it produces a wrapped struct type
property. When the wrapped struct type property is used to create a property that applies @racket[value-contract] to the value associated
new struct type (via @racket[struct], @racket[make-struct-type], etc), with the property when used to create a new struct type (via
it applies @racket[value-contract] to the value associated with the @racket[struct], @racket[make-struct-type], etc).
property.
The contract has no effect on the struct type property accessor. The struct type property's accessor function is not affected; it must
be protected separately.
@examples[#:eval the-eval @examples[#:eval the-eval
(define-values (prop prop? prop-ref) (module propmod racket
(make-struct-type-property 'prop)) (require racket/contract
unstable/prop-contract)
(define-values (prop prop? prop-ref)
(make-struct-type-property 'prop))
(define (prop-app x v)
(((prop-ref x) x) v))
(provide/contract
[prop? (-> any/c boolean?)]
[prop (struct-type-property/c
(-> prop? (-> number? boolean?)))]
[prop-app (-> prop? number? boolean?)])
(provide prop-ref))
(define/contract wrapped (module structmod racket
(struct-type-property/c (-> any/c (-> number? number?))) (require 'propmod)
prop) (struct s (f) #:property prop (lambda (s) (s-f s)))
(provide (struct-out s)))
(struct s (f) (require 'propmod 'structmod)
#:property wrapped (lambda (s) (s-f s))) (define s1 (s even?))
(prop-app s1 5)
(prop-app s1 'apple)
(define (get-f s) ((prop-ref s) s)) (define s2 (s "not a fun"))
(prop-app s2 5)
(define s1 (s add1)) (define s3 (s list))
((get-f s1) 5) (prop-app s3 5)
((get-f s1) 'apple)
(define s2 (s (lambda (n) (if (zero? n) 'zero 'nonzero)))) ((prop-ref s3) 'apple)
((get-f s2) 5)
((get-f s2) 'apple)
] ]
The first contract error above is a simple function contract violation
on @racket[prop-app]. The second and third contract errors above blame
the @racketidfont{structmod} module, because it accepted the struct type
property contract. To avoid blame, @racketidfont{structmod}
should have placed a contract on @racket[s]. The final contract error,
involving @racket[s3], blames @racketidfont{propmod} because the struct
type property contract obliges @racketidfont{propmod} to make sure the
property's value is not misused, but @racketidfont{propmod} allows
direct access to the property value via @racket[prop-ref]. To
avoid blame, @racketidfont{propmod} should remove the export of
@racket[prop-ref] or protect it with a contract.
} }
@close-eval[the-eval] @close-eval[the-eval]