Doug McIlroy writes: | In Hugs 1.4, ++ was an operator of class Monad; in Hugs 98 it is | an operator on lists. I've looked in the Hugs documentation and | haven't found anything about the change (probably a failing of | mine, not the documentation). | | Anyway, that breaks some code in an article that's been accepted | for JFP, wherein I overloaded ++ by placing the operand type in | class Monad. This doesn't work any more. | | I don't want to publish code that doesn't work, and I don't want | to give up that overloading, which is completely natural. Can | you shed any light on what happened between the two versions? | Or offer an idea about how to rescue the overloading? Hi. It was in the transition from Haskell 1.4 to Haskell 98 that (++) was taken out of class MonadPlus and became list-specific. I think it had something to do with simplifying error messages. MonadPlus is still there, but the overloaded operator in question is now called `mplus`. Regards, Tom