[racket-dev] [plt] Push #24906: master branch updated

Great, thanks!

Robby

On Mon, Jun 25, 2012 at 8:28 PM, Asumu Takikawa <asumu at ccs.neu.edu> 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