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

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.