How to calculate how many recursive calls happened in this Haskell function?

Question

I\'ve been trying to figure this out for a couple of hours now. I need to calculate how many recursive calls happened using a certain function:

maximum\' ::         


        

Answer 1

Do you love functional programming? Do you love imperative programming? Why not have both! Here's a recursive-imperative way to count the recursion depth.

{-# LANGUAGE FlexibleContexts #-}

import Control.Monad.State

maximumWithCount :: (Ord a, MonadState Int m) => [a] -> m a
maximumWithCount xs = case xs of
  [] -> error "empty list"
  [x] -> return x
  (x:xs) -> do
    modify (+1)  -- increment the counter because we're recursing!
    y <- maximumWithCount xs
    return $ max x y

λ runState (maximumWithCount [1,2,3,4,5,4,3,2,1]) 0
(5,8)