9 Nov
2009
9 Nov
'09
11:40 a.m.
Excerpts from Henk-Jan van Tuyl's message of Mon Nov 09 11:10:07 +0100 2009:
Either is not a monad, you can check this by typing :i Either in GHCi; you will not see a line like instance Monad Either in the result. Compare this to :i Maybe
In fact the Either Monad instance is defined in the 'transformers' (or 'mtl') packages. However for this reason among others you may want to use the 'attempt'[1] package instead of Either. [1]: http://hackage.haskell.org/package/attempt-0.0.0 -- Nicolas Pouillard http://nicolaspouillard.fr