[GHC] #8755: Happy parser file compilation causes panic

[GHC]

#8755: Happy parser file compilation causes panic
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        Reporter:  wting               |            Owner:
            Type:  bug                 |           Status:  new
        Priority:  normal              |        Milestone:
       Component:  Compiler            |          Version:  7.6.3
      Resolution:                      |         Keywords:
Operating System:  Unknown/Multiple    |     Architecture:  x86_64 (amd64)
 Type of failure:  Compile-time crash  |       Difficulty:  Unknown
       Test Case:                      |       Blocked By:
        Blocking:                      |  Related Tickets:
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Comment (by wting):

 Sorry, this also fails on 7.4.1:

 {{{
 ╭─ting at sloth ~/code/cs345  ‹python-2.7.3›  ‹hw2›
 ╰─➤  ghc DeclareParse.hs
 [1 of 4] Compiling Base             ( Base.hs, Base.o )
 [2 of 4] Compiling Lexer            ( Lexer.hs, Lexer.o )
 [3 of 4] Compiling Declare          ( Declare.hs, Declare.o )
 [4 of 4] Compiling DeclareParse     ( DeclareParse.hs, DeclareParse.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.4.1 for x86_64-unknown-linux):
         Prelude.head: empty list

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 I'm going to try and investigate further.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8755#comment:1>
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