Using StaticArrow to track the number of steps in a computation.

gistfile1.hs

module Main where

import Data.Monoid
import Control.Monad
import Control.Applicative
import Control.Arrow
import Control.Arrow.Transformer
import Control.Arrow.Transformer.Static

type SteppedIO a b = StaticArrow ((,) (Sum Int)) (Kleisli IO) a b

step :: (a -> IO b) -> SteppedIO a b
step cmd = wrap (Sum 1, Kleisli cmd)

countSteps :: SteppedIO a b -> Int
countSteps = getSum . fst . unwrap

exec :: SteppedIO a b -> a -> IO b
exec =  runKleisli . snd . unwrap 

program :: SteppedIO () ()
program =
    step (\_ -> putStrLn "What is your name?")  
    >>>
    step (\_ -> getLine)
    >>>
    step (putStrLn . mappend "Hello, ")

main :: IO ()
main = do
    putStrLn $ "Number of steps: " ++ show (countSteps program)
    exec program ()