[GHC] #13021: Inaccessible RHS warning is confusing for users

[GHC]

#13021: Inaccessible RHS warning is confusing for users
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           Reporter:  mpickering     |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  PatternMatchWarnings               |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The pattern match checker makes the distinction between redundant matches
 and matches with an inaccessible right hand side.

 A pattern with an inaccessible RHS, is a redundant pattern which forces
 the argument so affects strictness.

 I think this is confusing for users as most of the time you write programs
 assuming totality but the error message doesn't make it clear why the two
 warnings are different. I think that instead they should both be called
 redundant but a note added to the inaccessible case explaining that
 removing it could affect strictness.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13021>
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