#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:21 simonpj]:
> The way to generate dictionaries is to call the type checker. As
described in the Commentary
http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/HscMain, and
http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler, the type
checker takes a `(HsExpr Name)`, with no `HsWrap` constructors, and
returns an `(HsExpr Id)`, replete with `HsWrap` constructors that do the
dictionary application.
>
This paragraph is from
[http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/TypeChecker].
The functions referred to, including `sourceTypeRep` are maybe part of the
old typechecker?
Of particular interest are the variants SourceTy and NoteTy of
TypeRep.Type. The constructor SourceTy :: SourceType -> Type represents a
type constraint; that is, a predicate over types represented by a
dictionary. The type checker treats a SourceTy as opaque, but during the
translation to core it will be expanded into its concrete representation
(i.e., a dictionary type) by the function
[[GhcModule(compiler/types/Type.lhs])).sourceTypeRep. Note that newtypes
are not covered by SourceTypes anymore, even if some comments in GHC still
suggest this. Instead, all newtype applications are initially represented
as a NewTcApp, until they are eliminated by calls to
[[GhcModule(compiler/types/Type.lhs])).newTypeRep.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4459#comment:23>
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