indexed_colors2.elm

import Dict

type Painting = {palette: [Color], grid: [[Int]]}

model: Painting
model = {
  palette = [red, orange, yellow, green, blue, purple],
  grid = [[0,1,2,3,4,5], [1,2,3,4,5,0], [2,3,4,5,0,1]] }

indexed: [a] -> Dict.Dict Int a
indexed list = Dict.fromList (zip [0..(length list)] list)

type Palette = Dict.Dict Int Color

makePalette: [Color] -> Palette
makePalette colors = indexed colors

colorAt: Palette -> Int -> Color
colorAt p i = case Dict.lookup i p of
      Just c -> c
      Nothing -> black

cellAt: Palette -> Int -> Int -> Form
cellAt p x i = moveX (toFloat (5 + x * 10)) (filled (colorAt p i) (rect 10 10))

rowAt: Palette -> Int -> [Int] -> Form
rowAt p y pixels = moveY (toFloat (-5 - y * 10)) (group (zipWith (cellAt p) [0..(length pixels)] pixels))

render: Painting -> Element
render m = 
  let width = 10 * (length (head m.grid))
      height = 10 * (length m.grid)
      palette = makePalette m.palette
      image = (group (zipWith (rowAt palette) [0..(length m.grid)] m.grid))
  in
    collage width height [move (toFloat(-width)/2, toFloat(height)/2) image]

rotate: [a] -> [a]
rotate l = concat [(tail l), [head l]]

step: Float -> Painting -> Painting
step _ prev = { palette = rotate prev.palette, grid = prev.grid }

frames: Signal Painting
frames = foldp step model (every second)

main: Signal Element
main = lift render frames