[Haskell-cafe] Re: Optimization problem
robdockins at fastmail.fm
Tue Sep 19 09:40:10 EDT 2006
On Sep 19, 2006, at 8:52 AM, Conor McBride wrote:
> Hi folks
> apfelmus at 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
Speak softly and drive a Sherman tank.
Laugh hard; it's a long way to the bank.
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