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

[Miguel Mitrofanov]

> module Main where
>
>
>
> data SquareType numberType = Num numberType => SquareConstructor  
> numberType
>
>
>
> class ShapeInterface shape where
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>       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
>

Awesome! That's the first e-mail I see that looks good in HTML!
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