Re: [GHC] #15753: Inconsistent pattern-match warnings when using guards versus case expressions

4 Jan 2019

      #15753: Inconsistent pattern-match warnings when using guards versus case
expressions
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.10.1
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15884, #16129    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by sjakobi):

 Replying to [comment:6 RyanGlScott]:

 Not sure if this is a useful reduction:

 {{{#!hs
 {-# LANGUAGE PatternSynonyms #-}
 module Bug where

 {-# COMPLETE Id #-}
 pattern Id :: () -> ()
 pattern Id a = a

 bug :: () -> ()
 bug ia
   | Id a <- id ia
   = a
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15753#comment:7
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler