Re: Proposal: Foldable typeclass: make foldl' and foldr' class methods

On Mon, Jun 20, 2011 at 12:02 PM, Duncan Coutts wrote:

This should not break much code. In particular it should not break existing type class instance declarations since there is a default definition for instances that don't defined the new methods.

The only potential breakage is that foldl' and foldr' are exported via Foldable(..) rather than directly. This could affect modules that use explicit imports.  (I consider this fact to be a slightly unfortunate quirk of the Haskell module system).

What would the broken code look like? GHC 6.12 handles:

import Module (classMethod)

just fine, even when 'classMethod' is exported only via:

module Module (MyClass(..))

I haven't tested this too extensively - only with 'runghc'. Antoine