I think this is exactly what you need. You could write (< (assert s
integer?) 0) or (and s (integer? s) (< s 0)), which mostly do the same
thing.
But the fundamental issue is that this program is well-typed:
(process (list (cons 'size "hi")))
since that's a perfectly valid `OptList`. If you didn't have a dynamic
check in `process`, you'd end up with (< "hi" 0) which is wrong.
If that's not what you want, what should the restrictions on `OptList` be?
Sam
On Sun, Nov 30, 2014 at 8:46 AM, Manfred Lotz <manfred.l...@arcor.de> wrote:
> Well, I should have added that I've found this:
>
> (: process (-> OptList Void))
> (define (process ol)
> (let ([s (optval 'size ol)])
> (if (and s (< (cast s Integer) 0))
> (displayln "wrong value")
> (displayln "ok")))
> )
>
>
> but I didn't find this really nice. Actually, I was hoping for
> something more concise.
>
> --
> Manfred
>
>
> On Sun, 30 Nov 2014 10:13:48 +0100
> Manfred Lotz <manfred.l...@arcor.de> wrote:
>
>> Hi there,
>> I've got another problem with typed racket.
>>
>> Let us say I have an assoc list with options for a program. These
>> options could be of type String, Boolean, or Integer.
>>
>> Now in my program I want to check certain options but I don't know how
>> to do without Typed Racket screaming at me.
>>
>> Here a minimal example:
>>
>> #lang typed/racket
>>
>> (define-type Myopt (U String Boolean Integer))
>> (define-type OptList (Listof (Pairof Symbol Myopt)))
>>
>>
>> (: olist OptList)
>> (define olist (list '(dir . ".")
>> '(verbose . #t)
>> '(size . 12)))
>>
>> (: optval (-> Symbol OptList Myopt))
>> (define (optval v ol)
>> (let ([val (assoc v ol)])
>> (if val
>> (cdr val)
>> (error "Unexpected option encountered"))))
>>
>> (: process (-> OptList Void))
>> (define (process ol)
>> (if (< (optval 'size ol) 0)
>> (displayln "wrong value")
>> (displayln "ok")))
>>
>>
>> I get an error:
>> Type Checker: type mismatch
>> expected: Real
>> given: Myopt
>> in: (optval (quote size) ol)
>>
>>
>> How could I solve this?
>>
>>
>
>
>
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