[GHC] #11952: automatic show instance generating loop

[GHC]

#11952: automatic show instance generating loop
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           Reporter:  maxigit   |             Owner:
               Type:  bug       |            Status:  new
           Priority:  normal    |         Milestone:
          Component:  Compiler  |           Version:  7.10.3
           Keywords:            |  Operating System:  Unknown/Multiple
       Architecture:  x86       |   Type of failure:  None/Unknown
          Test Case:            |        Blocked By:
           Blocking:            |   Related Tickets:
Differential Rev(s):            |         Wiki Page:
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 I have the following code :

 {{{#!hs
 {-# LANGUAGE TypeFamilies, DataKinds #-}

 data Status = Valid | Invalid deriving(Show)

 data A s = A (TF s)

 type family TF (s:: Status) where
     TF Valid = Int
     TF Invalid = Either String Int

 instance Show (A Valid)
 instance Show (A Invalid)

 a :: A Valid
 a = A 3
 }}}
 Printing `a` results in a stackoverflow.

 I'm using GHC-7.10.3 (and 7.8.4) on Ubuntu under a VM

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11952>
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