[Haskell-cafe] classes for data structures

[Wolfgang Jeltsch]

Am Mittwoch, 6. Februar 2008 16:12 schrieb Jules Bean:
> And indeed there *will* be a Monad, if there is a sensible way of
> defining concat :: b (b a) -> b a, which there probably is.

Not with sets.  “concat” on Set would have type

    Ord a => Set (Set a) -> Set a

instead of

    Set (Set a) -> Set a.

Best wishes,
Wolfgang