On Jun 22, 2009, at 14:43 , Andrew Coppin wrote:
data Foobar a where Foo :: X -> Y -> Foobar NoZoo Bar :: X -> Y -> Foobar NoZoo Zoo :: Foobar NoZoo -> Foobar ZooFor some reason, if I do this I get endless type check errors. I have to change the top two back to Foobar a before it will work. *sigh*
That's probably because ghc can't fix a type for Foobar a if you never actually use a anywhere. Functional dependencies could solve that, but giving ghc a way to infer a type for it by using it where it doesn't affect anything important is easier and doesn't risk possible(?) weird interactions between FDs and GADTs.
-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
PGP.sig
Description: This is a digitally signed message part
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
