[GHC] #7089: -fwarn-unused-do-bind with type families

[GHC]

#7089: -fwarn-unused-do-bind with type families
------------------------------+---------------------------------------------
 Reporter:  dag               |          Owner:                  
     Type:  bug               |         Status:  new             
 Priority:  normal            |      Component:  Compiler        
  Version:  7.4.1             |       Keywords:                  
       Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
  Failure:  None/Unknown      |       Testcase:                  
Blockedby:                    |       Blocking:                  
  Related:                    |  
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 When using acid-state, I get warnings for "unused do binds" from functions
 that return {{{()}}} but whose type involve asssociated types:


 {{{
 update :: UpdateEvent event => AcidState (EventState event) -> event -> IO
 (EventResult event)
 }}}


 Shouldn't GHC be able to deduce when {{{EventResult}}} resolves to unit?

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7089>
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