[GHC] #15716: GHC hangs on default implementation of type family

7 Oct 2018

      #15716: GHC hangs on default implementation of type family
-------------------------------------+-------------------------------------
           Reporter:  Heimdell       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:
          Component:  Compiler       |           Version:  8.4.1
           Keywords:                 |  Operating System:  Linux
       Architecture:  x86_64         |   Type of failure:  Compile-time
  (amd64)                            |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I have this code:

 {{{
 {-# language TypeFamilies #-}
 {-# language MultiParamTypeClasses #-}
 {-# language FlexibleInstances #-}

 import Control.Monad.Except

 class Component comp where
     data Error comp :: *
     type ComponentT comp :: * -> *
     type ComponentT comp = ExceptT (Error comp)

 }}}

 I expect it to either compile or fail with error.

 Instead, GHC[i] hangs every time.

 It prints
 {{{
 <interactive>:10:28: error:
 }}}

 and then hangs.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15716
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