On Wednesday 19 September 2007, Janis Voigtlaender wrote: > Hi, > > the Prelude docs found via > > http://haskell.org/hoogle/hoodoc.cgi?module=Prelude&name=Functor&mode=class > > claim that there is an instance > > Functor ((,) a) > > And yet, I get (in GHC, but similarly in Hugs): > > Prelude> fmap (+1) (undefined,2) > > <interactive>:1:0: > No instance for (Functor ((,) a)) > arising from use of `fmap' at <interactive>:1:0-22 > Possible fix: add an instance declaration for (Functor ((,) a)) > In the expression: fmap ((+ 1)) (undefined, 2) > In the definition of `it': it = fmap ((+ 1)) (undefined, 2) > > What do I have to import to get the Functor ((,) a) instance? > > (Of course, I can define it myself, but this is not the point.)
In GHC 6.6 and above, you'll need to import Control.Monad.Instances (a bit of a weird place to put it, but I guess there's no Control.Functor and such). If you have an earlier version than that, I'd say import Control.Monad.Writer at a guess. -- Dan _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell