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

[Jules Bean]

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