On Fri, 2008-10-03 at 20:43 +0100, Andrew Coppin wrote:
David Menendez wrote:
It wasn't until fairly recently that people realized that you could do useful things if you had "return" and "ap", but not (>>=), which why we have some unfortunate limitations in the Haskell prelude, like Applicative not being a superclass of Monad.
This leads to all the duplication between Applicative and Monad. In a perfect world, we would only need the Applicative versions.
OK. So it's broken "for compatibility" then? (Presumably any time you change something from the Prelude, mass breakage ensues!)
I'm not a big fan of backward-compatibility myself, but changing Monad to be a sub-class of Applicative actually would have broken every monad instance in existence (at the time Applicative was added, since it didn't have any instances yet). I don't know what proportion of Haskell programs/libraries/etc. have at least one Monad instance in them, but I would guess it's high. jcc