[GHC] #9636: Function with type error accepted

[GHC]

#9636: Function with type error accepted
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              Reporter:  augustss    |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 For what it's worth, I don't have a strong opinion either way. I think we
 are agreed that:

  * In an user-written type signature,
  * if an application of a closed type family is "apart" from all equations
 of the family,
  * then we should signal either an error or a warning.

 Lennart says "error", Richard says "warning", and I can't work up much
 excitement about which is chosen.  One advantage of "error" is that you
 don't have to add a flag to suppress the warning!

 Anyway, if someone wants to implement it, go ahead!

 This all applies to ''user-written type signatures''.  I don't want to
 apply this to "types that appear during the type inference process"
 because I don't know exactly what that might mean.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9636#comment:6>
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