[GHC] #11245: Non-exhaustive pattern, "Patterns not matched" list is empty

[GHC]

#11245: Non-exhaustive pattern, "Patterns not matched" list is empty
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        Reporter:  osa1              |                Owner:  gkaracha
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 I see your point about this not being a bug, but can't we have a better
 error message? For example:

 {{{
 Exhaustive.hs:10:7: warning:
     Pattern match(es) are non-exhaustive
     In the definition for ‘a’: Cases not matched:
       (Just i <- x), not (odd i)
 }}}

 Maybe it's hard to get that "cases not matched" so exactly, but at least
 we can say vaguely that the guards are incomplete, instead of the error
 suggesting that a list follows but then omitting the list.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11245#comment:3>
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