[GHC] #15471: Polymorphism, typed splices and type inference don't mix

[GHC]

#15471: Polymorphism, typed splices and type inference don't mix
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        Reporter:  mpickering        |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Template Haskell  |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 But that doesn't scale well
 {{{
 foo2 :: Num a => a -> a
 foo2 x = x+1

 test_foo2 :: ???
 test_foo2 = [|| foo2 |]]
 }}}
 If you give it the type `test_foo2 :: forall a. Num a => Q (TExp (a->a))`
 then you'll need to decide what dictionary to pass to it when you invoke
 it in `$$(test_foo2)`.

 Only erasure is allowing MetaOCaml to squeeze by, and we don't have that
 luxury.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15471#comment:11>
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