[GHC] #14107: Implement Semigroup and Monoid instances for the ST monad

[GHC]

#14107: Implement Semigroup and Monoid instances for the ST monad
-------------------------------------+-------------------------------------
           Reporter:  plato          |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Core           |           Version:  8.2.1
  Libraries                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Since IO implements `Semigroup` and `Monoid`, is there a good reason for
 `ST` not to implement those, too? I discovered the lack of those instances
 while using `foldMap` for code that used to use `IO` as the underlying
 monad.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14107>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler