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

30 Dec 2015

      #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 gkaracha):

 Henceforth, a non-exhaustiveness warning about a match for which guards
 are responsible
 (the match has no arguments so incompleteness appears due to guards not
 covering all possible
 cases), a better warning will be printed. E.g. for the example above, the
 warning issued will be:
 {{{
 T11245.hs:12:7: warning:
     Pattern match(es) are non-exhaustive
     In an equation for ‘a’:
         Guards do not cover entire pattern space
 }}}
 There is probably (probably because it is always subject to the
 performance cost) room for
 improvement, like printing more details concerning failure, but I think I
 can safely close
 this ticket now.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11245#comment:8
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