On Thu, Jan 5, 2012 at 3:32 PM, Rian Hunter
hello
i'm getting inconsistent monomorphism behavior with the same code only depending on whether or not -XTypeFamilies is enabled:
Which version of GHC are you using? Starting with GHC 7.0, the TypeFamilies extension implies the MonoLocalBinds language feature, which looks like what you're running into. Here's a blog post from the GHC folks about it: http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7 Antoine
---- {-# LANGUAGE TypeFamilies #-}
snda :: a -> b -> b snda ba = id
main = do let ma = (return () :: IO ()) mBox bb = snda ma bb
mBox $ return (4 :: Int) mBox $ return "G"
return () ----
in the preceding example, if -XTypeFamilies is enabled then "mBox" is monomorphic and the program will terminate early, otherwise, it's polymorphic and the program will complete successfully.
i think i understand why this is the case but i couldn't find documentation on this inconsistency anywhere. is this expected behavior or is this a bug in GHC? thanks!
rian
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