Let me resend the code...as it stands....
module Main where
data SquareType numberType = Num numberType => SquareConstructor
numberType
class ShapeInterface shape where
area :: Num numberType => shape->numberType
data ShapeType = forall a. ShapeInterface a => ShapeType a
instance (Num a) => ShapeInterface (SquareType a) where
area (SquareConstructor side) = side * side
and the errors are for the instance declaration.......
[1 of 1] Compiling Main ( Main.hs, C:\Documents and
Settings\nichom\Haskell\Shapes2\out/Main.o )
Main.hs:71:36:
Couldn't match expected type `numberType' against inferred type `a'
`numberType' is a rigid type variable bound by
the type signature for `area' at Main.hs:38:15
`a' is a rigid type variable bound by
the instance declaration at Main.hs:70:14
In the expression: side * side
In the definition of `area':
area (SquareConstructor side) = side * side
I'm becoming lost in errors I don't comprehend....
What bamboozles me is it seemed such a minor enhancement.
________________________________
From: d4ve.menendez@gmail.com [mailto:d4ve.menendez@gmail.com] On Behalf
Of David Menendez
Sent: 21 December 2007 17:05
To: Nicholls, Mark
Cc: Jules Bean; haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] nice simple problem for someone
struggling....
On Dec 21, 2007 11:50 AM, Nicholls, Mark