EXAMPLE MODULE

> module Shape (Shape(Rectangle, Ellipse),
>               Radius, Side, Vertex,
>               square, circle, area
>              ) where
> 
> data Shape = Rectangle Side Side
>            | Ellipse Radiaus Radius
>          deriving Show
> 
> type Radius = Float
> type Side = Float
> type Vertex = (Float, Float)
> 
> square s = Rectangle s s
> circle r = Ellipse r r
> area :: Shape -> Float
> area (Rectangle s1 s2) = s1 * s2
> area (Ellipse r1 r2) = pi * r1 * r2
> mars = Ellipse 1 1.093