[plt-scheme] A couple of contract questions

Let me also reccomend the chapter on contracts in the Guide.

Robby

On 8/16/08, Matt Jadud <jadudm at gmail.com> wrote:
> Hi Gregory,
>
> On Sat, Aug 16, 2008 at 6:30 PM, Woodhouse Gregory
> <gregory.woodhouse at gmail.com> wrote:
>> How do I write a contract for a function that takes no arguments (i.e., a
>> thunk)?
>
> (define/contract foo
>   (-> number?)
>   (lambda () 42))
>
>> Is it possible to write a contract specifying the return value
>> for a function like
>> (lambda (x) (lambda (y) (+ x y)))
>
> (define/contract bar
>   (-> (-> number? number?))
>   (lambda () (lambda (n) 42)))
>
> Or, if you prefer,
>
> (define/contract greg
>   (-> number? (-> number? number?))
>   (lambda (x) (lambda (y) (+ x y))))
>
>> ((greg 4) 2)
> 6
>> ((greg 4) 'two)
> . . 5:4: 5:3 broke the contract
>   (-> number? (-> number? number?))
> on greg; expected <number?>, given: two
>
> You can be more specific:
>
> (define/contract specific-greg
>   (-> (and/c number? even?) (-> (and/c number? odd?) number?))
>   (lambda (x) (lambda (y) (+ x y))))
>
>> ((specific-greg 2) 3)
> 5
>> ((specific-greg 3) 2)
> . . 5:4: 5:3 broke the contract
>   (->
>    (and/c number? even?)
>    (-> (and/c number? odd?) number?))
> on specific-greg; expected <(and/c number? even?)>, given: 3
>
> I think I'm using 402 under OSX.
>
> Cheers,
> Matt
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