[GHC] #1460: Problem with Monoid instance of Data.Map

[GHC]

#1460: Problem with Monoid instance of Data.Map
-----------------------------+----------------------------------------------
  Reporter:  ahey at iee.org    |          Owner:                 
      Type:  proposal        |         Status:  new            
  Priority:  normal          |      Milestone:                 
 Component:  libraries/base  |        Version:  6.6.1          
  Severity:  normal          |       Keywords:  Data.Map Monoid
Difficulty:  Easy (1 hr)     |             Os:  Multiple       
  Testcase:                  |   Architecture:  Multiple       
-----------------------------+----------------------------------------------
See..

 [http://www.haskell.org/pipermail/libraries/2007-May/007491.html]

 Data.Map Monoid instance is currently..

 {{{
 instance (Ord k) => Monoid (Map k v) where
     mempty  = empty
     mappend = union
     mconcat = unions
 }}}

 ..but probably should be..

 {{{
 instance (Ord k, Monoid v) => Monoid (Map k v) where
  mempty            = empty
  mappend map0 map1 = unionWith mappend map0 map1
  mconcat maps      = foldr (unionWith mappend) empty maps
 }}}

 Adrian Hey

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1460>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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