[Haskell-cafe] Re: Optimization problem

[Conor McBride]

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

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

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