Elimination of absurd patterns (reformatted)

Brent Yorgey byorgey at seas.upenn.edu
Tue May 3 03:26:27 CEST 2011

On Mon, May 02, 2011 at 09:25:06PM +0000, C Rodrigues wrote:
> I'm re-sending this e-mail, hopefully with proper line breaks this time.
> 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?

Not a real answer to your question, but have you tried this with GHC
7.0.3? The type checker changed a lot between 6.12 and 7 and it may
now behave more consistently (although I do not know for sure).


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