[GHC] #2238: panic nameModule tpl_B1{v}

[GHC]

#2238: panic nameModule tpl_B1{v}
-------------------------+--------------------------------------------------
    Reporter:  claus     |        Owner:         
        Type:  bug       |       Status:  new    
    Priority:  normal    |    Milestone:         
   Component:  Compiler  |      Version:  6.9    
    Severity:  normal    |   Resolution:         
    Keywords:            |     Testcase:         
Architecture:  Unknown   |           Os:  Unknown
-------------------------+--------------------------------------------------
Comment (by claus):

 btw, before the panic, this was meant to pin down an issue with TFs (vs
 FDs), where TFs don't improve types sufficiently for instance selection.
 compare:
 {{{
 *Main> :t undefined :: CTF Bool how => how
 undefined :: CTF Bool how => how :: HowTF Bool
 *Main> :t undefined :: CFD Bool how => how
 undefined :: CFD Bool how => how :: A
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2238#comment:1>
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