mapM /= traverse?

Simon Marlow marlowsd at
Mon May 11 19:15:59 UTC 2015

I was hoping that in GHC 7.10 we would make mapM = traverse for lists, 
but it appears this isn't the case: the Traversable instance for lists 
overrides mapM to be the manually-defined version in terms of foldr.

Why is this?  Fusion?

Unfortunately since I want mapM = traverse (for Haxl) I'll need to 
continue to redefine it in our custom Prelude.


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