[Haskell-cafe] fmap vs. liftM

Felipe Lessa felipe.lessa at gmail.com
Tue Feb 5 16:51:18 EST 2008

On Feb 5, 2008 6:06 PM, Dan Weston <westondan at imageworks.com> wrote:
> Can you do this with a GHC rule? Something like:
> {-# RULES
>        "join_dot_fmap_return/id"  forall x . join (fmap return x) = x
> #-}
> Dan

I guess this would make use of the rule (otherwise the transformation
would change the code's semantic) but would not enforce that the rule
itself is valid (which is undecidable).



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