On Sep 19, 2006, at 8:52 AM, Conor McBride wrote:
Hi folks
apfelmus@quantentunnel.de wrote:
Btw, why are there no irrefutable patterns for GADTs? I mean, such a sin should be shame for a non-strict language...
Just imagine
data Eq a b where Refl :: Eq a a
coerce :: Eq a b -> a -> b coerce ~Refl a = b
I think you mean:
coerce ~Refl x = x
coerce undefined True :: String
Bang you're dead. Or rather... Twiddle you're dead.
Moral: in a non-total language, if you're using indexing to act as evidence for something, you need to be strict about checking the evidence before you act on it, or you will be vulnerable to the blandishments of the most appalling liars.
As Randy Pollack used to say to us when we were children, the best thing about working in a strongly normalizing language is not having to normalize things.
All the best
Conor
Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG