Great, thanks! Robby
On Mon, Jun 25, 2012 at 8:28 PM, Asumu Takikawa <[email protected]> wrote: > On 2012-06-25 20:15:49 -0500, Robby Findler wrote: >> This is not directly related to your particular commit, but if I make >> a make-prime-dict, does apply a contract at that point (using >> 'contract')? If so, who are the parties that get blamed? > > The short answer is: the generated contract can be applied, for example, > in the range of a constructor and the blame is from whatever contract > boundary it was applied at. > > Longer: I'll explain by way of example. Suppose you define a generic > interface: > > (define-generics simple-dict > (dict-ref simple-dict key [default]) > (dict-set simple-dict key val) > (dict-remove simple-dict key)) > > then you define an implementation of it (perhaps in a different module): > > (define-struct some-dict (v) > #:methods gen:simple-dict > [...]) > > then you can provide a constructor from that implementing module that > contracts the resulting instance: > > (provide/contract > [make-int-dict > (-> key-value-list? > (simple-dict/c > [dict-ref (->* (simple-dict? symbol?) (any/c) integer?)] > [dict-set (-> simple-dict? symbol? integer? simple-dict?)] > [dict-remove (-> simple-dict? symbol? simple-dict?)]))])) > > You could also provide the same constructor under a different contract > (with a subset of the operations if you want): > > (provide/contract > [make-prime-dict > (-> key-value-list-of-primes? > (simple-dict/c > [dict-set (-> simple-dict? symbol? prime? simple-dict?)]))])) > > Instances made with these constructors will have the appropriate checks > when you use `dict-set` on them. > > Cheers, > Asumu _________________________ Racket Developers list: http://lists.racket-lang.org/dev
