Monomorphism restriction - is this still needed for efficiency?

[Simon Marlow]

Brian Hulley wrote:

> I'm wondering if the monomorphism restriction is now just an anachronism 
> from Haskell 98 or if it is still needed for efficiency ie should I just 
> now use -fno-monomorphism-restriction when compiling all my code to 
> consign it to the dustbin of history? :-)
> 
> A related question is, if it can still improve efficiency when applied 
> to local bindings, whether it would be worthwhile to have an additional 
> option to switch monomorphism off for top level bindings but still keep 
> it for local bindings, since I can't think of any situation where I 
> don't want a top level binding to be fully polymorphic.
> 
> Does anyone know of any situation where a top level binding should not 
> be fully polymorphic?

The discussion on the monomorphism restriction on the haskell-prime list 
recently should help you:

http://www.haskell.org//pipermail/haskell-prime/2006-February/000252.html

I measured what happened to the nofib suite with 
-fno-monomorphism-restriction.  The answer was, on the whole, "not 
much".  But there were a couple of programs that got worse.

It's a matter of personal taste whether you should use 
-fno-monomorphism-restriction, I wouldn't like to emphatically declare 
one way or the other which is best.

Cheers,
	Simon