On Mon, Jan 30, 2012 at 3:37 PM, Sam Tobin-Hochstadt <sa...@ccs.neu.edu> wrote: > On Mon, Jan 30, 2012 at 3:22 PM, John Clements > <cleme...@brinckerhoff.org> wrote: >> Am I missing something obvious in either of these? > > No. Typed Racket doesn't have type subtraction, which is what you > need in the first case. I'm not sure why the second case isn't working > right; I think the type of `filter' is a little too restrictive.
Thinking more about the second case, the problem is that you want the type of `pair?' to be: (All (A) (A -> Boolean : A \intersect (Pairof Any Any)) But the type of `pair?' is: (Any -> Boolean : (Pairof Any Any)) which is equivalent in the first-order case, but not in the higher-order case, as when used as the argument to `filter'. -- sam th sa...@ccs.neu.edu ____________________ Racket Users list: http://lists.racket-lang.org/users
