drunken-monad identity monad example posted by Leo @ Sun, 06 Mar 2011 05:42:14 +0000

in looking at the body of the treasureMap function on page 304 (“Building a Monad from Scratch”), I am trying to figure out how to parse the expression:

pos >>==
stagger>>==
stagger>>==
crawl>>==
rtn

how is this parsed by GHC? (right associative or left associative >>==)
Like this(right associative >>==)?

pos >>==
(stagger>>==
(stagger>>==
(crawl>>==
rtn)))

or like this(left associative >>==)?

(((pos >>==
stagger>>==)
stagger>>==)
crawl>>==)
rtn

The first(right-associative) would seem to transform like so:
form0: pos >>== (stagger>>== (stagger>>== (crawl>>== rtn)))
...form1: (stagger>>== (stagger>>== (crawl>>== rtn))) (pos)
...form2 (stagger>>== (crawl>>== rtn)) (stagger (pos))
...form3 (crawl>>== rtn) (stagger (stagger (pos)))
....form4 rtn (crawl (stagger (stagger (pos))))

I think I fudged it a bit to make the parentheses work right. My confusion is, for example, in step :
what does (crawl>>==rtn) mean? This can’t be right since crawl>>==return evaluates to return(crawl). Either I’m missing some sort of function composition operator in my rewriting or my transformation is wrong.

Thanks for your help