[Haskell-cafe] fmap vs. liftM

[Felipe Lessa]

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).

Cheers,

-- 
Felipe.