Int vs Word performance?

[Simon Marlow]

Claus Reinke wrote:
>>> Here is a trivial example with drastic difference between
>>> T = Int and T = Word (~2.5x here):
>>>
>>>    main = print $ foldl' (+) 0 [1..100000000::T]
> ..

> A quick grep shows almost no specialization at all for Word, or for
> IntXX/WordXX (see below). Still, none of that seems to explain the
> example repeated at the top of this message.

The Enum instance for Int uses specialised implementations of enumFromTo 
and friends, whereas the Word version uses the generic integralEnumFromTo.

Cheers,
	Simon