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)>] > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
