Re: [Haskell-cafe] nice simple problem for someone struggling....

Nicholls, Mark wrote:

*instance* ShapeInterface SquareType *where*

area (SquareConstructor sideLength) = sideLength * sideLength

*data* SquareType a = Num a => SquareConstructor a

Now you have changed your type from SquareType to SquareType a, you need to change the instance to: instance ShapeInterface (SquareType a) where... Jules