#lang racket
(module x racket
(provide
(contract-out
(rename f g (-> integer? any/c))))
(define f displayln))
(require 'x)
(g 'a)
On Aug 27, 2014, at 2:18 PM, Kevin Forchione <[email protected]> wrote:
>
> On Aug 27, 2014, at 11:12 AM, Matthias Felleisen <[email protected]> wrote:
>
>>
>> On Aug 27, 2014, at 12:22 PM, Kevin Forchione <[email protected]> wrote:
>>
>>>
>>> #lang racket
>>>
>>> (provide (contract-out [foo
>>> (-> string? list?)])
>>> (rename-out (foo bar)))
>>>
>>> (define (foo n) (list n))
>>>
>>> (module+ test
>>> (require (submod ".."))
>>> (foo 3)
>>> (bar "3”))
>>>
>>> Here foo violates the contract. Changing the argument to foo to “3” and
>>> the argument to bar to 3 shows that bar does not violate the contract. So
>>> the contract is bound to foo and not to the rename. Quite interesting!
>>>
>>
>>
>> contract-out attaches a contract to foo so when you can call foo on 3, you
>> get an error.
>>
>> provide also exports foo as bar w/o contract, so you can call it on anything
>> you want.
>>
>> This is clearly what the words of the program imply, and the semantics of
>> the language gives it to you. No problems!
>
> Yes, I agree. Very useful! Is there a way to attach a contract to a renamed
> identifier? I tried wrapping contract around a rename form and it didn’t
> appear to like it.
>
> -Kevin
>
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