[plt-scheme] In Typed Scheme, type for sub1 doesn't include (Integer -> Integer)

There will be soon, e.g., n in Nat such that even? is true, too. Sam  
has been working on this and it should come out soon -- Matthias



On Apr 20, 2009, at 11:23 AM, Todd O'Bryan wrote:

> Any reason why?
>
> The following doesn't work:
>
> (: ! (Integer -> Integer))
> (define (! n)
>  (cond
>    [(zero? n) 1]
>    [else (* n
>             (! (sub1 n)))]))
>
> but change (sub1 n) to (- n 1) and it works fine.
>
> Also, is there any way to define subtypes? For example, could I define
> a "natural-number" type that's limited to non-negative integers?
>
> Thanks,
> Todd
>
> P.S. Typed Scheme is fun to play with. :-)
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