30 Dec
2009
30 Dec
'09
6:15 p.m.
I would use:
foldm :: Monoid m => [m] -> m
Which is just a better implementation of mconcat / fold. The reason I prefer this interface is that foldm has a precondition in order to have a simple semantics: the operator you're giving it has to be associative. I like to use typeclasses to express laws.
That's a valid point. Unfortunately, Haskell is not Coq, so there is no guarantee that the monoid laws are actually satisfied. And using a type-class has the downside that you can have only one instance per type. Maybe, you want to use both `foldm (+) 0' and `foldm (*) 1'. So the bottom-line is that you should have both versions. Cheers, Ralf