[GHC] #1816: Add Data.Set.mapMaybe

[GHC]

#1816: Add Data.Set.mapMaybe
-----------------------------+----------------------------------------------
  Reporter:  guest           |          Owner:         
      Type:  proposal        |         Status:  new    
  Priority:  normal          |      Milestone:  Not GHC
 Component:  libraries/base  |        Version:  6.8    
  Severity:  normal          |       Keywords:         
Difficulty:  Unknown         |             Os:  Unknown
  Testcase:                  |   Architecture:  Unknown
-----------------------------+----------------------------------------------
 This function is also available for lists (from Data.Maybe) and Maps
 (Data.Set).
 The semantics are straightforward:
 {{{
 mapMaybe f = fromList . catMaybes . map f . toList
 }}}

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1816>
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