Re: [Haskell-cafe] MonadPlus instance for IO

Am Mittwoch, 2. Februar 2005 14:17 schrieb David Roundy:

I'm sure I'm doing something stupid, but somehow ghc isn't recognizing the existance of a MonadPlus instance for IO:

DarcsIO.lhs:48: No instance for (MonadPlus IO) arising from use of `mplus' at DarcsIO.lhs:48 In the definition of `foo': foo = (fail "aaack") `mplus` (fail "foobar")

Any idea what I'm doing wrong? I'm using

$ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.2.2

packaged for debian.

Probably you haven't imported 'Control.Monad.Error', where the instance is defined. I did and all went well. Cheers, Daniel