Cube.hs

module Geometry.Cube
( volume
, area
) where
import qualified Geometry.Cuboid as Cuboid
volume :: Float -> Float
volume side = Cuboid.volume side side side
area :: Float -> Float
area side = Cuboid.area side side side

Cuboid.hs

module Geometry.Cuboid
( volume
, area
) where
volume :: Float -> Float -> Float -> Float
volume a b c = rectArea a b * c
area :: Float -> Float -> Float -> Float
area a b c = rectArea a b * 2 + rectArea a c * 2 + rectArea c b * 2
rectArea :: Float -> Float -> Float
rectArea a b = a * b

geo.hs

import qualified Geometry.Sphere as Sphere
import qualified Geometry.Cuboid as Cuboid
import qualified Geometry.Cube as Cube

main = do
  print $ Cube.volume 4.0

Sphere.hs

module Geometry.Sphere
( volume
, area
) where
volume :: Float -> Float
volume radius = (4.0 / 3.0) * pi * (radius ^ 3)
area :: Float -> Float
area radius = 4 * pi * (radius ^ 2)