[racket] [typed racket] type case

On Thu, Oct 20, 2011 at 3:08 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
> Does typed racket fail to typecheck because cond will return void on negative numbers or something more related to exhaustive checking regardless of return value?

The former.  Since there's no pattern matching in "core" Racket, it's
not even clear what exhaustiveness would mean in that case.

> -Ian
> ----- Original Message -----
> From: Sam Tobin-Hochstadt <samth at ccs.neu.edu>
> To: Eric Tanter <etanter at dcc.uchile.cl>
> Cc: Racket Users <users at racket-lang.org>
> Sent: Thu, 20 Oct 2011 14:39:19 -0400 (EDT)
> Subject: Re: [racket] [typed racket] type case
>
> There are basically two options here:
>
> 1. If you just use `cond' with no `else', you get a type error when
> your cases are not exhaustive. For example:
>
> (: f ((U String Integer) -> Boolean))
> (define (f x)
>  [(string? x) (string=? x "hi")]
>  [(exact-nonnegative-integer? x) (= x 7)])
>
> This program will fail to typecheck.
>
> 2. For the particular case of the PLAI `cases' form, Eli and I have
> built something for his class which uses Typed Racket, but the
> exhaustiveness checking is done by `cases' itself.  Lots more about
> that is available from Eli's class web page [1], and I'm sure he'd be
> happy to give you the code.
>
> [1] http://pl.barzilay.org/
>
> On Thu, Oct 20, 2011 at 10:48 AM, Eric Tanter <etanter at dcc.uchile.cl> wrote:
>> Hi again,
>>
>> Is there a mechanism to do an exhaustive type case?
>>
>> I know I can use (cond [(type-pred? v) ...]
>>                       [...])
>>
>> but of course I have no guarantee that I am exhaustive (and of course, doing pattern matching to destruct the value would be even nicer).
>>
>> Basically, I guess I'm after the typed version of PLAI's type-case.
>>
>> Thanks,
>>
>> -- Éric
>>
>>
>>
>> _________________________________________________
>>  For list-related administrative tasks:
>>  http://lists.racket-lang.org/listinfo/users
>>
>
>
>
> --
> sam th
> samth at ccs.neu.edu
>
> _________________________________________________
>  For list-related administrative tasks:
>  http://lists.racket-lang.org/listinfo/users
>
>



-- 
sam th
samth at ccs.neu.edu