RE: foralls in class assertions

19 Jul 2002

      At 2002-02-20 13:15, Simon Peyton-Jones wrote:
...
OK, so it does look as though it's the same idea as 
that described in our paper.   Good.
I have not implemented, yet.
I don't suppose you did for GHC 5.04?...
...
As always my implementation
priorities are strongly influenced by my perception of whether
some enhancement would be used.  Maybe you can outline
why such a change would be useful to you?  I only have the
example in our paper as motivation so far.
I just thought of another motivating example for this:

  class Monoid a where
    mempty :: a
    mappend :: a -> a -> a
    mconcat :: [a] -> a

  class (
    Monad m,
    forall a. Monoid m a
    ) => MonadPlus m

Of course, you folks might not want to rewrite Control.Monad.MonadPlus. 
But I think is shows this sort of thing is useful in principle (and it 
would great for my HBase, which does its own Prelude).

-- 
Ashley Yakeley, Seattle WA