[Haskell-cafe] nice simple problem for someone struggling....
Nicholls.Mark at mtvne.com
Fri Dec 21 11:37:06 EST 2007
Really....I'm sure I tried that...(as it seemed obvious) ... and it
failed....but I'll have another go....
From: Jules Bean [mailto:jules at jellybean.co.uk]
Sent: 21 December 2007 15:33
To: Nicholls, Mark
Cc: haskell-cafe at haskell.org
Subject: Re: [Haskell-cafe] nice simple problem for someone
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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