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

[Brent Yorgey]

>
> "class ShapeInterface shape where
>        area :: shape->Int"
>
> now looks dubious....I want it to be something like
>
> "class ShapeInterface shape where
>        area :: Num numberType => shape->Int" ?
>

Rather, I think you probably want

class ShapeInterface shape where
    area :: Num numberType => shape -> numberType

-Brent
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