[Haskell-cafe] what is inverse of mzero and return?

[S. Alexander Jacobson]

I assume there is a standard name for this 
class/function:

   instance Foo [] where
     foo [] = mzero
     foo (x:_) = return x

   instance Foo (Maybe x) where
     foo Nothing = mzero
     foo Just x = return x


-Alex-





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