Re: [Haskell-cafe] MonadPlus m => Maybe a -> m a

On Sat, Jul 28, 2012 at 8:00 AM, Thiago Negri wrote:

I'm solving this exercise:

http://www.haskell.org/haskellwiki/All_About_Monads#Exercise_4:_Using_the_Mo...

I'm missing a function to transform a Maybe a into a MonadPlus m => m a. I did search on Hoogle with no luck.

There is no standard definition for the "g" function I'm defining?

g :: (MonadPlus m) => Maybe a -> m a

g Nothing = mzero g (Just a) = return a

I doubt there is a "standard" named function for this, since conversions between monads are typically not "unique" and there are lots and lots of pairs of monads you can convert between. You can define g in terms of Data.Maybe.maybe as: g = maybe mzero return