Displace implicit function

displaced.hs

import Prelude
import Control.Applicative (pure)
import Graphics.Implicit
import Graphics.Implicit.Definitions
import Graphics.Implicit.Primitives

displaced
  :: (Object obj vec)
  => (vec -> Double)
  -> obj
  -> obj
displaced dispFn obj = implicit
  (\i -> 
    let prim = getImplicit obj i
        disp = dispFn i
    in prim + disp
    )
  -- XXX
  ((*2) <$> getBox obj)

mul (V3 a b c) = a * b * c
-- main = writeSTL 1 "displaced.stl"  $ displaced (\v@(V3 x y z) -> mul ( (cos . (*(2))) <$> v ) ) $ sphere 10
main = writeSTL 1 "displaced.stl"  $ displaced (\v@(V3 x y z) -> mul ( 
  V3 (sin . (*(2)) $ x)
     (cos . (*(1/2)) $ y)
     (sin z)
  ) ) $ sphere 10