Elimination of absurd patterns

Felipe Almeida Lessa felipe.lessa at gmail.com
Tue May 3 04:03:23 CEST 2011

On Mon, May 2, 2011 at 6:20 PM, C Rodrigues <red5_2 at hotmail.com> wrote:
> I was experimenting with using GADTs for subtyping when I found something
> interesting.  Hopefully someone can satisfy my curiosity.
> Here are two equivalent GADTs.  My understanding was that GHC would
> translate "Foo" and "Bar" into isomorphic data types.  However, GHC 6.12.3
> generates better code for 'fooName' than for 'barName'.  In 'fooName', there
> is no pattern match against 'FooExtra'.  In 'barName', there is a pattern
> match against 'BarExtra'.  What makes these data types different?

IIRC, GHC 6.12.3 had some problems with type equalities.  Did you try GHC 7.0.3?

Cheers, =)


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