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

5 Sep 2018

      #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 mpickering):

 I still claim there is some bug here for two reasons.

 1. The result is unusable after splicing.
 2. A very similar program using static pointers works fine.

 {{{
 foo = static (id :: forall a . a -> a )

 foo2 = [|| id :: forall a . a -> a ||]
 }}}

 In GHCi

 {{{
...
(deRefStaticPtr foo) 'a'
 'a'
...
($$(foo2)) 5
<interactive>:89:12: error:
     • No instance for (Num Any) arising from the literal ‘5’
     • In the first argument of ‘$$(foo2)’, namely ‘5’
       In the expression: ($$(foo2)) 5
       In an equation for ‘it’: it = ($$(foo2)) 5

 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15471#comment:5
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