[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 augustss):

 I would like it to apply to types that appear during type checking,
 because I think it's an error and errors should be reported.  I presume
 that at some point during type checking the closed type family equations
 are used to simplify a type.  If at that point you discover that none of
 the equations can possibly match, then that should be reported as an
 error.

 If irreducible closed type family (type) expressions are allowed then
 these are some kind of "ghost types".  If we agree that that only "data"
 and "newtype" generate types, then these ghosts are some new kind of types
 that have no meaning.  They are not empty types, they simply malformed.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9636#comment:7>
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