[GHC] #12386: Infinite loop when showing type family error

[GHC]

#12386: Infinite loop when showing type family error
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           Reporter:  elliottt       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 When attempting to load this code in ghci with ghc-8.0.1, I get an
 infinite loop while it attempts to display the error:

 {{{
 {-# LANGUAGE TypeFamilies #-}

 class C a where
   type family F a t :: *

   type family T a :: *
   type T a = F a
 }}}

 {{{
 catbug :: ~/Scratch/ast-experiment » ghci test.hs
 GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /Users/trevor/.ghci
 [1 of 1] Compiling Main             ( test.hs, interpreted )

 test.hs:7:14: error:
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12386>
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