Proposal: Export Data.Word.Word from Prelude

[Evan Laforge]

On Wed, Aug 13, 2014 at 3:06 PM, Ben Millwood <haskell at benmachine.co.uk> wrote:
> `length :: [a] -> Word` (or things of that ilk) would be even more of a
> mistake, because type inference will spread that `Word` everywhere, and `2 -
> 3 :: Word` is catastrophically wrong.

This is a pretty convincing argument for me.  I have in the past used
Word for things that seemed like they should always be positive, and
pretty quickly reverted back to a signed type.  All you need is a
subtraction anywhere and the chance of underflow is very high.  And,
as Ben said, it's easy for the "always positive" type to wind up in a
domain where subtraction is valid due to type inference.  The
principled thing might be to make that a different type, but in
practice that can be a lot of hassle so it often doesn't happen (do
you use NonEmpty everywhere possible? always have separate types for
absolute and relative measures? sometimes it's not worth the clutter).