[Haskell-cafe] nice simple problem for someone struggling....
jules at jellybean.co.uk
Fri Dec 21 10:33:26 EST 2007
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...
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