{-# LANGUAGE NoMonomorphismRestriction #-}

module Main where

import Data.Monoid
import Control.Applicative
import Control.Monad.Writer.Strict
import System

data BTree = Leaf | Node BTree BTree

inc = tell (Sum 1)

leaf = inc >> return Leaf
node a b = inc >> return (Node a b)

make 0 = leaf
make depth = do
 t1 <- make (depth - 1)
 t2 <- make (depth - 1)
 node t1 t2

main = do
  depth <- depthArgs <$> getArgs
  let counter = getSum . execWriter . make $ depth
  print counter
    where
      depthArgs :: [String] -> Int
      depthArgs [] = 10
      depthArgs [x] = read x

{-
$ ghc --make -O2 -no-recomp Foo.hs
[1 of 1] Compiling Main             ( Foo.hs, Foo.o )
Linking Foo ...
$ time ./Foo 23
16777215

real    0m0.005s
user    0m0.004s
sys     0m0.000s
-}