On Jan 30, 2012, at 12:53 PM, Sam Tobin-Hochstadt wrote: > 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))
Yes, I agree, and intersection types occurred to me in this case too. I assume you're speaking hypothetically: TR doesn't support intersections, does it? John
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