[GHC] #13306: Problems with type inference for static expressions

[GHC]

#13306: Problems with type inference for static expressions
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        Reporter:  edsko             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 The error about `f9` makes sense because after dictionary translation the
 syntactic restriction is no longer met:
 {{{#!hs
 f9 dTa dTNIa = static (f7 dTa)
 }}}
 From `static f7` you could get a `StaticPtr (forall a. Typeable a => U a
 -> NonInj a -> NonInj a)`, if that were legal. But in order to get a `U a
 -> NonInj a -> NonInj a` you need to combine the (static) `f7` with a (not
 static) `Typeable` dictionary.

 The other errors all involve `StaticPtr (NonInj a -> NonInj a)`, with a
 type argument that does not determine `a`. I'm not sure whether this is
 okay (or useful); it feels potentially dubious, but I can't see concretely
 why it would be bad.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13306#comment:3>
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