Thank you. I assumed when I saw this:   "we could use Maybe's mplus to define a function, parent s = (mother s) `mplus` (father s)" that mplus was *already* present in Maybe. Michael --- On Fri, 5/1/09, Neil Mitchell <ndmitchell@gmail.com> wrote: From: Neil Mitchell <ndmitchell@gmail.com> Subject: Re: [Haskell-cafe] chr/ord? To: "michael rice" <nowgate@yahoo.com> Cc: "haskell-cafe@haskell.org" <haskell-cafe@haskell.org>, "Anton van Straaten" <anton@appsolutions.com> Date: Friday, May 1, 2009, 6:32 AM Hi

But I get this when I try to use it:

sheep.hs:30:22: Not in scope: `mplus' [michael@localhost ~]$

You need to import Control.Monad. You can find answers to these sorts of questions with Hoogle: http://haskell.org/hoogle/?hoogle=mplus Thanks Neil