[racket] Typed racket and hash table

On Fri, 27 Jun 2014 15:59:47 -0400
"Alexander D. Knauth"
<alexander at knauth.org> wrote:

> Are you sure you meant "hash-ref!" and not just "hash-ref”?
> 

Well I thought hash-ref! is the way to go because I just wanted #f in
case of not found.

> Because even with (hash-ref! my-hash size (lambda () #f)), it would
> expect the #f to be of type (Listof String), which it isn’t.  
> 

Oops, that makes the difference. Using hash-ref works fine now.
It seems that in untyped racket hash-ref! is fine but it is not suited
for typed racket.

Thanks a lot, Manfred



> On Jun 27, 2014, at 3:32 PM, Manfred Lotz
> <manfred.lotz at arcor.de> wrote:
> 
> > I tried this:
> > 
> > #lang typed/racket/base
> > 
> > (: my-hash (HashTable Nonnegative-Integer (Listof String)))
> > (define my-hash (make-hash))
> > 
> > 
> > 
> > (: my-hash-add (-> Nonnegative-Integer String Void))
> > (define (my-hash-add size s)
> >  (let* ([val (hash-ref! my-hash size #f)])
> >    (if val
> >        (hash-set! my-hash size (cons s val))
> >        (hash-set! my-hash size (list s)))))
> > 
> > and got:
> > 
> > test.rkt:10:14: Type Checker: Polymorphic function `hash-ref!' could
> > not be applied to arguments: Argument 1:
> >  Expected: (HashTable a b)
> >  Given:    (HashTable Nonnegative-Integer (Listof String))
> > Argument 2:
> >  Expected: a
> >  Given:    Nonnegative-Integer
> > Argument 3:
> >  Expected: (-> b)
> >  Given:    False
> > 
> >  in: (hash-ref! my-hash size #f)
> >  context...:
> >   /home/manfred/racket/share/pkgs/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt:249:0:
> >  type-check /home/manfred/racket/share/pkgs/typed-racket-lib/typed-racket/tc-setup.rkt:40:0:
> >  tc-setup /home/manfred/racket/share/pkgs/typed-racket-lib/typed-racket/typed-racket.rkt:25:4
> >   standard-module-name-resolver
> > 
> > 
> > What can I do to make this work?
> > 
> > 
> > -- 
> > Manfred
> > 
> > 
> > 
> > 
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