[racket] Possible issue in the typed version of foldl

Thank you for the speedy fix, and thank goodness I'm not just crazy

On Mon, Oct 20, 2014 at 2:45 PM, Vincent St-Amour <stamourv at ccs.neu.edu>
wrote:

> Thanks for the report!
>
> I pushed a fix earlier today.
>
> Vincent
>
>
>
> At Sun, 19 Oct 2014 23:16:11 -0700,
> Jack Firth wrote:
> >
> > I think there may be a mistake in the type definition of foldl for the
> case
> > that accepts an initial value and three lists and a function of four
> values
> > to fold them over. The following untyped code runs correctly:
> >
> > #lang racket
> > (define (f a b c d) d)
> > (define ns '(0 1 2))
> > (define vs '(a 2 "b"))
> > (foldl f 'ok ns ns vs)
> >
> > However, the typed form of this code gives a type error:
> >
> > #lang typed/racket
> > (define: (f [a : Natural] [b : Natural] [c : Any] [d : Symbol]) : Symbol
> d)
> > (: ns (Listof Natural))
> > (define ns '(0 1 2))
> > (: vs (Listof Any))
> > (define vs '(a 2 "b"))
> > (foldl f 'ok ns ns vs)
> >
> > Specifically, the type checker outputs:
> >
> > Type Checker: Polymorphic function `foldl' could not be applied to
> arguments:
> > Types: (-> a b c d d) d (Listof a) (Listof b) (Listof d) -> d
> >        (-> a b c c) c (Listof a) (Listof b) -> c
> >        (-> a b b) b (Listof a) -> b
> > Arguments: (-> Nonnegative-Integer Nonnegative-Integer Any Symbol
> > Symbol) 'ok (Listof Nonnegative-Integer) (Listof Nonnegative-Integer)
> > (Listof Any)
> > Expected result: AnyValues
> >  in: (foldl f (quote ok) ns ns vs)
> >
> > I think the issue may be in that first line of the type definition, (->
> a b
> > c d d) d (Listof a) (Listof b) (Listof d) -> d. Shouldn’t that last
> > argument type be (Listof c) instead of (Listof d)?
> > ​
> > [1.2  <text/html; UTF-8 (quoted-printable)>]
> >
> > [2  <text/plain; us-ascii (7bit)>]
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