[plt-scheme] Contract question

You have to pin down the arity enough that users of your function know
what the legal argument lengths are. (Is that what you're asking?)

Robby

At Mon, 23 Jan 2006 23:58:08 +0000, pedro pinto wrote:
>  One more question, how would I go about saying something about the return
> type of proc/func? From my understanding of the docs I need to write a
> function contract, as opposed to what I think is a flat-contract like
> arity-matches-lists, but I did not see a way to write one that does not also
> pin down the arity.
> 
> -pp
> 
> 
> 
> >  On 1/23/06, Robby Findler <robby at cs.uchicago.edu> wrote:
> > >
> > > You have to use the more complex combinators to express that. Here's
> > > how ->r can be used to express map's contract:
> > >
> > > (module map-c mzscheme
> > > (require (lib "contract.ss"))
> > >
> > > (define map-c map)
> > >
> > > (provide/contract
> > >   [map-c
> > >    (->r ([func
> > >           (and/c
> > >            procedure?
> > >            (let ([arity-matches-lists
> > >                   (λ (f)
> > >                     (procedure-arity-includes? f (+ 1 (length
> > > rest-args))))])
> > >              arity-matches-lists))]
> > >          [lst-one (listof any/c)])
> > >         rest-args
> > >         (and/c (listof (listof any/c))
> > >                (let ([same-length-lists (λ (x) (apply equal? (length
> > > lst-one) (map length x)))])
> > >                  same-length-lists))
> > >         (listof any/c))]))
> > >
> > > (require map-c)
> > >
> > > (define (print-msg exn)
> > > (display (exn-message exn))
> > > (newline))
> > >
> > > (map-c (lambda (x y) x) (list 1 2 3) (list 4 5 6))
> > > (with-handlers ([values print-msg])
> > > (map-c (lambda (x) x) (list 1 2 3) (list 4 5 6)))
> > > (with-handlers ([values print-msg])
> > > (map-c (lambda (x y) x) (list 1 2 3) (list 4 5 6 7)))
> > >
> > > At Mon, 23 Jan 2006 19:49:34 +0000, pedro pinto wrote:
> > > > Hi there,
> > > >
> > > > I just started fumbling around with contracts and I was trying to
> > > write a
> > > > contract for a function similar to map:
> > > >
> > > > map proc clist1 clist2 ... -> list
> > > >
> > > > Is there a way to say that proc is a procedure whose arity should
> > > match the
> > > > number of clist arguments?
> > > >
> > > > TIA,
> > > > -pp
> > > > _________________________________________________
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> > >
> >
> >