[racket] Typed racket problem

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.lotz at 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?
> 
>