[GHC] #11409: Cannot instantiate literals using TypeApplications

[GHC]

#11409: Cannot instantiate literals using TypeApplications
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        Reporter:  Feuerbach         |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1-rc1
      Resolution:                    |             Keywords:
                                     |  TypeApplications
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11352            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Replying to [comment:4 adamgundry]:
 > See also #11352, which is about the same issue for the newfangled
 overloaded labels (and I guess overloaded string and rational literals
 should be treated similarly).

 OK, so that makes it more worth thinking about.

 >  I experimented with something like Simon's suggestion for overloaded
 labels, and found that error messages got worse, because it was no longer
 possible to give a `CtOrigin` that mentioned the overloaded label as the
 source.

 I don't understand why.
  * We continue to have a case in the type checker for integer literals, as
 now.
  * It elaborates the literal to `integerLit 3` with type `forall a. Num a
 => a`

 When we instantiate that type (which is delayed in the new
 `TypeApplication` world) we need a suitable `CtOrigin`.  We get that using
 `exprCtOrigin` (see `TcExpr.tcApp`).  It can produce a suitable origin for
 an integer literal, string -- or field label.

 So it seems ok to me.  Worth a try?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11409#comment:5>
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