----- Ursprüngliche Nachricht ----- Von: "rodrigo.bonifacio" <[EMAIL PROTECTED]> Datum: Freitag, August 17, 2007 3:11 pm Betreff: [Haskell-cafe] Basic question....
> Hi all. > > I want to create the following polymorphic type (EnvItem) that we > can apply two functions (envKey and envValue). I tried the following: > > > type Key = String > > > data EnvItem a = EnvItem (Key, a) > > > envKey :: EnvItem (Key, a) -> String > > envKey EnvItem (key, value) = key > > > envValue :: EnvValue(Key, a) -> a > > envValue EnvItem (key, value) = value > > But this is resulting in the error: [Constructor "EnvItem" must > have exactly 1 argument in pattern] > > I think this is a very basic problem, but I don't know what is wrong. You are simply missing some brackets: > envKey :: EnvItem (Key, a) -> String > envKey (EnvItem (key, value)) = key > envValue :: EnvValue(Key, a) -> a > envValue (EnvItem (key, value)) = value Ciao, Janis. _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
