Re: [Haskell-cafe] Is there a generic way to detect "mzero"?

On 26 March 2012 20:33, Ting Lei wrote:

can :: (MonadPlus m) => (a -> m b) -> a -> Bool can f x = case f x of             mzero -> False             _ -> True

In the first pattern `mzero' is just a variable and matches anything, as does `_'. So, naturally, both patterns overlap. I don't see any way to write this without requiring `Eq m'.