[GHC] #14109: GHC matches -- as a varsym when lexing a qvarsym

[GHC]

#14109: GHC matches -- as a varsym when lexing a qvarsym
-------------------------------------+-------------------------------------
           Reporter:  glguy          |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.1
  (Parser)                           |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Other
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 GHC seems only to exclude the line comment marker `--`  when lexing a
 varsym and not a qvarsym.

 This can be observed in the following code

 {{{
 module Demo where

 x Demo.-- y = (x,y)
 }}}

 Generating this surprising error message

 {{{
 /Users/emertens/Desktop/Demo.hs:3:3: error:
     Qualified name in binding position: Demo.--
 }}}

 and excludes this definition perhaps?
 {{{
 example f = Just.-- comment
             f
 }}}

 Which might either have lexed as `Just` `.` `-- comment`, or it might have
 lexed as `Just.-` `-`, but it probably shouldn't be the case that it's a
 qvarsym.

 At a minimum, the Haskell Report specifically excludes `--` from the
 varsym rule, so it can't support the qvarsym rule match that it is now.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14109>
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