[Haskell-cafe] Newbie Haskell optimization question

[Slavomir Kaslev]

Hello,

I am new to Haskell and I am having fun with it writing L-system
generator. I was very pleased with concise syntax. It's an order of
magnitude better than any C++, Lisp, etc program I've ever written or
read.

Doing algorithmic optimizations on my generator I ended up with 4
different versions (you can see the other 3 in the file attached). The
most optimal of them is:

import qualified Data.Map

type LSystemElement = (Char, [Int])
type LSystem = [LSystemElement]
type LSystemRules = Data.Map.Map Char (LSystemElement -> LSystem)

generate'' :: LSystemRules -> LSystem -> Int -> LSystem
generate'' rules axiom steps =
    concatMap (iterate f axiom !!) (ind !! steps)
    where
      ind = [0] : [g x | x <- ind]
          where
            g [] = []
            g [x] = [x, x + 1]
            g xs = xs ++ g (drop (length xs `div` 2) xs)
      f = concatMap $ \elem -> Data.Map.findWithDefault (\x -> [x])
(fst elem) rules elem

-- Tests
a (_, [x, y]) | y <= 2    = [('A', [x + 2, y + 2])]
              | otherwise = [('B', [2]), ('A', [x - 1, y - 1])]

b (_, [x]) | x <= 2    = [('C', [])]
           | otherwise = [('B', [x - 1])]

rules = Data.Map.fromList [('A', a), ('B', b)]
axiom = [('A', [2, 2])]

Now I am thinking of doing some language level optimizations. Can you
give me any (random) directions? Any style recommendations are welcome
as well.

Cheers.

-- 
Slavomir Kaslev
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