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

Jules Bean 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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