[racket] Contract for function with vararg

From: Roman Klochkov (kalimehtar at mail.ru)
Date: Sun Jun 29 21:10:07 EDT 2014

 I  reformulate my problem:
I need to make a chaperone, that checks only type of first arg. Is it possible?

If yes, I'll sumply make something like
(define (arity>=/c x)
    (λ (proc)
      (define arity (normalize-arity (procedure-arity proc)))
      (define max-arity
        (if (list? arity) (car (reverse arity)) arity))
      (or (arity-at-least? max-arity) 
          (>= max-arity x))))

(and/c (arity>=/c 2)
           (check-first-arg input-port?))

Sun, 29 Jun 2014 13:08:06 -0400 от "Alexander D. Knauth" <alexander at knauth.org>:
>You can use or/c to do this, as long as you guard them like this so that no more than one contract matches at a time:
> (and/c (procedure-has-arity/c 2) (-> input-port? any/c any))
> (and/c (procedure-has-arity/c 3) (-> input-port? any/c any/c any))
> (and/c (procedure-has-arity/c 4) (-> input-port? any/c any/c any/c any))
> (->* (input-port? any/c) #:rest list? any)
> )
>Or, you could use if/c from unstable/contract, or define a cond/c macro like this:
>(require unstable/contract)
>(define-syntax cond/c
>  (syntax-rules (else)
>    [(cond/c) none/c]
>    [(cond/c [else else-c])
>     else-c]
>    [(cond/c [pred then-c] clause ...)
>     (if/c pred
>           then-c
>           (cond/c clause ...))]))
>(cond/c [(procedure-has-arity/c 2) (-> input-port? any/c any)]
>        [(procedure-has-arity/c 3) (-> input-port? any/c any/c any)]
>        [(procedure-has-arity/c 4) (-> input-port? any/c any/c any/c any)]
>        [else (->* (input-port? any/c) #:rest list? any)])
>By the way it has to be procedure-has-arity/c, not procedure-includes-arity/c:
>(define (procedure-has-arity/c arity)
>  (define normalized-arity (normalize-arity arity))
>  (flat-named-contract
>   `(procedure-has-arity/c ,normalized-arity)
>   (λ (f)
>     (and (procedure? f)
>          (arity=? (procedure-arity f) normalized-arity)))))
>On Jun 29, 2014, at 8:00 AM, Roman Klochkov < kalimehtar at mail.ru > wrote:
>>How to make a contract, that accepts 
>>(-> input-port? any/c any)
>>(-> input-port? any/c any/c any)
>>(-> input-port? any/c any/c any/c any)
>>(->* (input-port? any/c) #:rest list? any)
>>So theare should be at least two args and first arg should be input-port.
>>Roman Klochkov ____________________
>> Racket Users list:
>>  http://lists.racket-lang.org/users

Roman Klochkov
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20140630/b104616c/attachment.html>

Posted on the users mailing list.