shapes.hs

module Shape where

import Data.List (nub)

data Circle = Circle { radius :: Float }

data Triangle = Triangle { a :: Float, b :: Float, c :: Float }

class Dimensions shape where
  name :: shape -> String
  perimeter :: shape -> Float
  area :: shape -> Float

triangleName :: Triangle -> String
triangleName t =
  case length $ nub [a t, b t, c t] of
    1 -> "equilateral"
    2 -> "isoceles"
    _ -> "scalene"

instance Dimensions Triangle where
  name t = triangleName t
  perimeter t = (a t) + (b t) + (c t)
  area t =
    let
      a' = a t
      b' = b t
      c' = c t
      s  = (a' + b' + c') / 2
    in
      sqrt(s * (s - a') * (s - b') * (s - c'))

instance Dimensions Circle where
  name circle = "circle"
  perimeter circle = 2 * pi * (radius circle)
  area circle = pi * (radius circle)^2