[GHC] #4296: The dreaded SkolemOccurs problem

[GHC]

#4296: The dreaded SkolemOccurs problem
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    Reporter:  simonpj           |        Owner:                                       
        Type:  bug               |       Status:  new                                  
    Priority:  normal            |    Milestone:                                       
   Component:  Compiler          |      Version:  6.12.3                               
    Keywords:                    |     Testcase:  indexed-types/should_compile/Simple20
   Blockedby:                    |   Difficulty:                                       
          Os:  Unknown/Multiple  |     Blocking:                                       
Architecture:  Unknown/Multiple  |      Failure:  None/Unknown                         
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 The "!SkolemOccurs" problem is a celebrated difficulty with combining (a)
 termination and (b) completeness, in this example:
 {{{
 type instance F [a] = [F a]
 f :: (F [a] ~ a) => ...
 }}}
 Currently we err on the side of completeness, and lose termination.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4296>
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