[GHC] #784: defining type of returned value

[GHC]

#784: defining type of returned value
----------------------------------------+-----------------------------------
  Reporter:  Bulat.Ziganshin at gmail.com  |          Owner:         
      Type:  bug                        |         Status:  new    
  Priority:  low                        |      Milestone:         
 Component:  Compiler                   |        Version:  6.4.2  
  Severity:  normal                     |     Resolution:         
  Keywords:                             |             Os:  Unknown
Difficulty:  Unknown                    |   Architecture:  Unknown
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Changes (by simonpj):

  * priority:  normal => low

Comment:

 I know what is going on here.  The key code is:
 {{{
 foo :: IO (ForeignPtr a) = undefined

 baz :: IO (ForeignPtr a)
 baz = undefined
 }}}
 Here, the binding of {{{foo}}} is supposed to bind {{{a}}}, while the type
 sig on {{{baz}}} uses {{{a}}}.  Unfortunately, the dependency analyser
 isn't taking scoped type variables into account, which is clearly a bug.

 The exact setup for scoped type variables is under review, so I'm
 reluctant to invest effort in fixing this (it's not entirely trivial).  So
 for now I'm going to leave it as an open bug with low priority.

 Workaround: don't use a pattern binding that binds a scoped type variable.
 My bet s that you didn't intend that in the first place.

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/784>
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