Main.elm

blur : Dict(Int,Int) Int -> ( Int, Int ) -> Int
blur cells ( x, y ) =
    let
        xs =
            range (x - 1) (x + 1)

        ys =
            range (y - 1) (y + 1)

        points =
            concatMap (\x -> map (\y -> ( x, y )) ys) xs

        ( sum, num ) =
            foldr
                (\p ( s, n ) ->
                    case Dict.get p cells of
                        Just h ->
                            ( sum + h, num + 1 ) --  ( s + h, n + 1 )

                        Nothing ->
                            ( s, n )
                )
                ( 0, 0 )
                points
    in
    sum // num