[Haskell-cafe] Are newtypes optimised and how much?

[Gregory Crosswhite]

On 10/20/10 4:09 AM, Simon Peyton-Jones wrote:
> No, this isn't optimised.  The trouble is that you write (map Foo xs), but GHC doesn't know about 'map'.  We could add a special case for map, but then you'd soon want (mapTree Foo my_tree).

How about a special case for fmap?  That seems like it should handle a 
lot of cases.

Cheers,
Greg