[racket-dev] contract-out

That's the best solution I've come up with, which is basically the
abstraction I suggested under #4.

sam th

On Sunday, September 25, 2011, Carl Eastlund wrote:

> How about we write a "define-toggle-contract-out" form, so everyone
> can define their own without actually implementing their own.
> Something like so:
>
> (define-toggle-contract-out my-contract-out #:disable) ;; comment out
> keyword to enable
> (provide (my-contract-out [thing thing/c]))
>
> Carl Eastlund
>
> On Sun, Sep 25, 2011 at 7:41 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
> > Everyone rolling their own is bad. We want people to contract their code,
> and they don't want to always pay for the overhead. #2 sounds the best,
> since that could be again abstracted over by the user, this time with one
> line instead of the sevel it takes to implement provide-cond-contract. This
> also has the advantage that the user can have access to any subforms someone
> else adds later.
> > -Ian
> > ----- Original Message -----
> > From: Sam Tobin-Hochstadt <samth at ccs.neu.edu>
> > To: J. Ian Johnson <ianj at ccs.neu.edu>
> > Cc: Matthew Flatt <mflatt at cs.utah.edu>, dev at racket-lang.org
> > Sent: Sun, 25 Sep 2011 11:34:39 -0400 (EDT)
> > Subject: Re: [racket-dev] contract-out
> >
> > On Sun, Sep 25, 2011 at 10:55 AM, J. Ian Johnson <ianj at ccs.neu.edu>
> wrote:
> >> Very nice! Is it easy to make a provide form that conditionally provides
> with contracts, such as Sam's provide-cond-contract in
> typed-scheme/utils/utils.rkt?
> >
> > The trouble with this is that it's not clear how it should be
> > controlled.  There are a few obvious possibilities:
> >
> > 1. There's a global flag for all of Racket which turns contracts on
> > and off.  It should be pretty clear that this is a bad idea.
> > 2. There's a form like `(contract-cond-out expr stuff ...)'  which
> > uses the contracts in `stuff' IFF `expr' is true.  This is easy to
> > implement, but pretty inconvenient to use.
> > 3. Something like the status quo, where everyone defines their own
> > thing, but maybe with some abstraction.
> > 4. A compiler flag.  We don't have anything like this, though,
> > currently, and it's not clear how it should work.
> >
> >
> >> -Ian
> >> ----- Original Message -----
> >> From: Matthew Flatt <mflatt at cs.utah.edu>
> >> To: dev at racket-lang.org
> >> Sent: Sat, 24 Sep 2011 09:41:17 -0400 (EDT)
> >> Subject: [racket-dev] contract-out
> >>
> >> The `racket/contract' and `racket' modules now provide `contract-out',
> >> which is a `provide' form for contracts. Use
> >>
> >>    (provide (contract-out ....))
> >>
> >> instead of
> >>
> >>    (provide/contract ....)
> >>
> >>
> >> There's one difference between `(provide (contract-out ....))' and
> >> `(provide/contract ....)': contract expressions in contract-out' are
> >> implicitly moved to the end of the module, which means that they can
> >> refer to variables that are defined later. For example, the following
> >> program works as you'd expect:
> >>
> >>  #lang racket
> >>
> >>  (provide (contract-out [mask-of (turtle? . -> . color?)])
> >>          turtle?
> >>          color?)
> >>
> >>  (define (turtle? v)
> >>   (memq v '(Leonardo Michelangelo Donatello Raphael)))
> >>  (define (color? v)
> >>   (memq v '(blue orange purple red)))
> >>
> >>  (define (mask-of t)
> >>   (match t
> >>     ['Leonardo 'blue]
> >>     ['Michelangelo 'orange]
> >>     ['Donatello 'purple]
> >>     ['Raphael 'red]))
> >>
> >>
> >> The `contract-out' form is implemented as a provide pre-transformer,
> >> which is a new kind of `provide' form that is now supported by
> >> `racket/provide-transform'.
> >>
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-- 
sam th
samth at ccs.neu.edu
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