Re: [Haskell] help with some basic code that doesn't work

On 2005-02-07 20:36:55 +0000, pablo daniel rey wrote:

data Dir = Left | Right | Up | Down data Piece = Vertical | Horizontal | CodeA | CodeB

the error i get :

Instances of (Eq Dir, Eq Piece) required for definition of chgDir

You try to compare Dir and Piece values without having told Haskell how the comparison should work. Haskell doesn't provide a default comparison funcition even for the really obvious cases like this, unless you tell it to using the "deriving" keyword: data Bool = False | True deriving (Eq,Ord,Show,Read) In your case, all you need is Eq, so you can skip the parentheses. -- Karl Hasselström, kha@treskal.com www.treskal.com/kalle