Hi! This is not all. If I compare performance of those two semantically same functions: castRayScene1 :: Ray -> ViewportDotColor castRayScene1 (Ray vd o d) = ViewportDotColor vd (castRay' noColor 0) where castRay' color@(VoxelColor _ _ _ alpha) depth | depth > depthOfField = color | alpha < 0.001 = castRay' pointColor (depth + distance') | alpha > 0.999 = color | otherwise = castRay' newColor (depth + distance') where (# pointColor, distance #) = worldScene (o <+> (d <* depth)) distance' = max 1 distance newColor = addColor color pointColor and: castRay :: World -> Ray -> ViewportDotColor castRay world (Ray vd o d) = ViewportDotColor vd (castRay' noColor 0) where castRay' color@(VoxelColor _ _ _ alpha) depth | depth > depthOfField = color | alpha < 0.001 = castRay' pointColor (depth + distance') | alpha > 0.999 = color | otherwise = castRay' newColor (depth + distance') where (# pointColor, distance #) = world (o <+> (d <* depth)) distance' = max 1 distance newColor = addColor color pointColor castRayScene2 :: Ray -> ViewportDotColor castRayScene2 = castRay worldScene is the program which uses castRayScene1 1.35 faster then the program which uses castRayScene2 (37 seconds versus 50 seconds). (Compiler with GHC 6.8.3 and -O2 switch. Program is executing almost just this function over and over again.) It is somehow award that passing function as an argument slow down the program so much. Is not Haskell a functional language and this such (functional) code reuse is one of its main points? Of course. I could use some preprocessor/template engine to change/find/replace castRay-like function into a castRayScene1 before compiling. But this somehow kills the idea of a compiler? Smart compiler. Which should do things for you? The same as my previous example. Where a hard-coded list was not optimized. (Like it would change during the execution.) It looks like my program would be interpreted and not compiled. Mitar