[GHC] #11265: Internal error, using pattern synonym as instance head

19 Dec 2015


      #11265: Internal error, using pattern synonym as instance head
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.3
           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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 {{{!#hs
 {-# LANGUAGE PatternSynonyms, DataKinds #-}

 pattern A = True

 class    F a
 instance F A
 }}}

 when loaded in ghci it results in an internal error

 {{{!#hs
 % g internal.hs
 GHCi, version 7.11.20151216: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( internal.hs, interpreted )

 internal.hs:5:12: error:
     • GHC internal error: ‘A’ is not in scope during type checking, but it
 passed the renamer
       tcl_env of environment: []
     • In the first argument of ‘F’, namely ‘A’
       In the instance declaration for ‘F A’
 Failed, modules loaded: none.
 Prelude>
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11265
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