[GHC] #4459: Polymorphic Data.Dynamic

[GHC]

#4459: Polymorphic Data.Dynamic
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    Reporter:  vivian                                |        Owner:  vivian      
        Type:  feature request                       |       Status:  new         
    Priority:  normal                                |    Milestone:  7.4.1       
   Component:  GHC API                               |      Version:  7.1         
    Keywords:  polymorphic, dynamic, class, linking  |     Testcase:              
   Blockedby:                                        |   Difficulty:              
          Os:  Unknown/Multiple                      |     Blocking:  4316        
Architecture:  Unknown/Multiple                      |      Failure:  None/Unknown
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Comment(by vivian):

 Replying to [comment:9 simonmar]:
 > I'm completely confused about what this ticket is asking for.  Could
 somebody explain in more detail please?  e.g. the ticket seems to be
 asking for something in the `Data.Dynamic` library, but then there's lots
 of talk about something in the GHC API.  What is `TypedAny`?

 This ticket is about adding support for polymorphic dynamic types, which
 would appear in `Data.Dynamic` or similar as a package, so that, for
 example, a variable `sort :: Ord a => [a] -> [a]` can be loaded at runtime
 (like `System.Plugins`) and then dynamically linked/typechecked against
 the variable to which it is applied.  Currently dynamics and plugins are
 limited by the monomorphic restriction.

 `TypedAny` (renamed to `DynamicHValue`) is supposed to be an opaque type
 that wraps an `HValue` and a `Type` via the GHC API.  [I have got this
 far, i.e. dynamically loaded code via GHC]

 [In an early incarnation I was able to apply a dynamically loaded ad hoc
 polymorphic function to a list and print the result]

 I listed this as a feature request against the GHC API because there need
 to be some additions 'under the hood' for this to work:

   1) a way of getting the type of an expression to the value level
 `ty <- GHC.modInfoLookupName` <-- okay for dynamically loaded code but not
 normal code

   2) a way of getting a 'type as value' to become the type of an
 expression
 `(unsafeCoerce hvalue) :: ty` <-- currently completely impossible

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4459#comment:10>
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