[GHC] #9558: "Illegal equational constraint" that might not be the users fault

[GHC]

#9558: "Illegal equational constraint" that might not be the users fault
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              Reporter:  rrnewton    |            Owner:
                  Type:  bug         |           Status:  closed
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.9
            Resolution:  invalid     |         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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Changes (by simonpj):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Reid is right.

 Is the change a good design choice?  In general I think "yes".  The
 language extensions are meant to say whether or not you are using a
 language extension in a module; and if you need an extension to write down
 the type of a function you are defining I think that yes, you are using
 the extension.

 But if it causes major backward-compatibility pain, that might have
 outweighed it (if we'd known).  But now 7.8 is out.

 I'll close this as invalid (since it is by-design), but if anyone feels
 strongly we should actually change back (in 7.10) to the previous design
 (where GHC would infer a type that you could not write in a type signature
 without adding more flags), then please open a new ticket to say so and
 why.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9558#comment:3>
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