monad_drunken.hs

module Main where
  -- モナド: 型構成子、 return、 バインド
  data Position t = Position t deriving (Show) -- 型構成子、 自家製モナド
  stagger (Position d) = Position (d + 2)
  crawl (Position d) = Position (d + 1)

  rtn x = x -- return のかわり
  x >>== f = f x -- bind(>>=) のかわり

  treasureMap pos = pos >>==
                    stagger >>== -- stagger pos >>==
                    stagger >>== -- stagger stagger pos >>==
                    crawl >>== -- crawl stagger stagger pos >>==
                    rtn -- crawl stagger stagger pos

You can use the state monad:

module Main where

    import Control.Monad.State

    stagger :: State Integer ()
    stagger = do
        d <- get
        put (d+2)

    crawl :: State Integer ()
    crawl = do
        d <- get
        put (d+1)

    treasureMap :: State Integer () 
    treasureMap = do
        stagger
        stagger
        crawl

    follow :: Integer -> Integer
    follow d = execState treasureMap d

Thanks, looks great!
I am just a beginner. Using monad is hard :<

My original code is in "Sevel Languages in Seven Weeks".
The author's intention is maybe learning HOW a monad works.

I think that monads can be easy and difficult at the same time. They can make the code very readable and easy to understand, but it can be difficult to create them.

In the code above I'm using "syntactic sugar" which makes the code more similar to imperative program code.