> nullify 6 on the Hugs command line: > > ERROR - Unresolved overloading > *** Type : (Num a, Null a) => a > *** Expression : nullify 6
Try 'nullify (6::Int)'. Hugs (not due to any fault of its own) doesn't know that 6 is supposed to be of type Int, so if you also had an instance 'Null Double', what should it do? > I then tried the following: > > instance Num a => Null a where > nullify x = 0 > > but got the following error in Hugs > > ERROR "C:\zero.hs":5 - Syntax error in instance head (constructor expected) This is because instance declarations like this are illegal. Basically, there has to be a constructor on the RHS of the =>. You can't just have a type variable. -98 on hugs and -fglasgow-exts on ghc should lift this restrictuion, though I think you need -fallow-undecidable-instances in ghc and something else in Hugs... - Hal -- Hal Daume III | [EMAIL PROTECTED] "Arrest this man, he talks in maths." | www.isi.edu/~hdaume _______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
