[GHC] #9428: Pretty printer bad formatting

[GHC]

#9428: Pretty printer bad formatting
-------------------------------------+-------------------------------------
       Reporter:  terrelln           |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  lowest             |               Milestone:
      Component:  Driver             |                 Version:  7.6.3
       Keywords:  pretty print       |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:  Other
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 When compiling with `-fwarn-incomplete-patterns`, the first test case
 `s17.hs` (attached) outputs unmatched patterns correctly.

 {{{
 test.hs:4:1: Warning:
     Pattern match(es) are non-exhaustive
     In an equation for `f':
         Patterns not matched:
             B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B
 _ B _
             B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B
 _ A B
             B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ A
 B B _
             B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ B _ A
 B A B
             ...
 }}}

 However, when compiling `s18.hs` each argument is printed on its own line.
 16 lines of the output are included below.

 {{{
 test.hs:4:1: Warning:
     Pattern match(es) are non-exhaustive
     In an equation for `f':
         Patterns not matched:
             B
             _
             B
             _
             B
             _
             B
             _
             B
             _
             B
             _
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9428>
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