sh.hs

import Shapes
main = do
  print $ nudge (baseCircle 30) 10 20

Shapes.hs

module Shapes
( Point, Shape, area, nudge, baseCircle, baseRect) where
data Point = Point Float Float deriving (Show)
data Shape = Circle Point Float |
             Rectangle Point Point deriving (Show)
area :: Shape -> Float
area (Circle _ r) = pi * r ^ 2
area (Rectangle (Point x1 y1) (Point x2 y2))
    = (abs $ x2 - x1) * (abs $ y2 - y1)
nudge :: Shape -> Float -> Float -> Shape
nudge (Circle (Point x y) r) a b = Circle (Point (x+a) (y+b)) r
nudge (Rectangle (Point x1 y1) (Point x2 y2)) a b
    = Rectangle (Point (x1+a) (y1+b)) (Point (x2+a) (y2+b))
baseCircle :: Float -> Shape
baseCircle r = Circle (Point 0 0) r
baseRect :: Float -> Float -> Shape
baseRect width height = Rectangle (Point 0 0) (Point width height)