On Saturday 29 May 2010 02:26:38, Ivan Lazar Miljenovic wrote: > Daniel Fischer <daniel.is.fisc...@web.de> writes: > > But if you want to have > > > > instance Monad (Either ConcreteType) where ... > > > > , you can have > > > > fail msg = Left someDefaultValue > > > > (or let the value depend on the message) and you can construct > > Left someMeaningfulValue in concrete situations. > > Which happens to make it identical to Maybe ;-)
If you use only the default value. But if you use more, making your type an instance of Error would be the sensible thing (unless you're one of the mtl-haters, but probably transformers has a similar instance). _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
