make fibonacci graphviz dot file

graph-fibonacci.hs

import Debug.Trace
import System.Environment
import System.IO

newtype S a =  S (Int, a) deriving (Show)
fib' :: S Int -> Int 
fib' (S (s, 0)) =  trace (show s ++ " [ label = " ++ show 0 ++ "]") 1
fib' (S (s, 1)) =  trace (show s ++ " [ label = " ++ show 1 ++ "]") 1
fib' (S (s, n)) = trace (show s ++ " [label = " ++ show n ++ "]") f1 + f2 
     where
        f1 = trace (show s ++ " -> " ++ show (s * 2 + 0)) $ fib' (S (s * 2 + 0, n - 1))
        f2 = trace (show s ++ " -> " ++ show (s * 2 + 1)) $ fib' (S (s * 2 + 1, n - 2))

fib :: Int -> Int
fib n = fib' (S (1, n))

main :: IO ()
main = do
  [n] <- getArgs
  hPutStrLn stderr "digraph fib {"       
  putStrLn $ show $ fib $ read n 
  hPutStrLn stderr "}"