[GHC] #10873: Bad error message for incorrect pattern synonym signature

[GHC]

#10873: Bad error message for incorrect pattern synonym signature
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        Reporter:  mpickering        |                Owner:  rdragon
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.2
  checker)                           |             Keywords:
      Resolution:  fixed             |  PatternSynonyms
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1866
       Wiki Page:                    |
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Changes (by bgamari):

 * status:  new => closed
 * resolution:   => fixed


Comment:

 This is greatly improved with the patch in comment:10. The original
 example now fails with,
 {{{
 Hi.hs:6:22: error:
     • No instance for (Show a)
         arising from the "provided" constraints claimed by
           the signature of ‘Pat’
       In other words, a successful match on the pattern
         Just a
       does not provide the constraint (Show a)
     • In the declaration for pattern synonym ‘Pat’
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10873#comment:11>
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