[GHC] #12683: Monad laws in terms of fishes (>=>)

10 Oct 2016


      #12683: Monad laws in terms of fishes (>=>)
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Documentation  |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:  #12672
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Present monad laws with Kleisli composition (fish operator)

 {{{#!hs
   return >=> g
 = g

   g >=> return
 = g

   (f >=> g) >=> h
 = f >=> (g >=> h)
 }}}

 instead of bind:

 {{{#!hs
   return a >>= k
 = k a

   m >>= return
 = m

   m >>= (\x -> k x >>= h)
 = (m >>= k) >>= h
 }}}

 Even though `>>=` is a method of `Monad` this is so much clearer that I
 think it's worth it, started as ticket:12672#comment:4

 ----

 Fun mention: [http://www.cse.chalmers.se/~jomoa/papers/quickspec2016.pdf
 QuickSpec] doesn't generate lambda terms so it will not discover `(xs >>=
 f) >>= g` = `xs >>= (\x -> f x >>= g)` so it needs to be in terms of
 `>=>`.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12683
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler