On Wed, May 16, 2012 at 05:41:33PM +0100, "Philip K. F. Hölzenspies" wrote:
>
> I'm trying to refactor the types in GHC (working on HEAD). First of all, I
> want to parameterise HsExpr et al to be parametric in the type representation
> (to remove the PostTcType type, which can not be instantiated before the type
> checker).
For what it's worth, I recently looked at doing this, but all the
options seemed to end up very ugly.
The most promising approach was using something like this:
data None = None
type family PostTc i t :: *
type instance PostTc RdrName a = None
type instance PostTc Name a = None
type instance PostTc Id a = a
---
data ForeignDecl name =
...
| ForeignExport (Located name)
(LHsType name)
(PostTc name Coercion)
but then you get GHC needing a "Data (PostTc id Coercion)" instance all
over the place, which would result in a lot of noise.
This could potentially be fixed by using DataKinds to close the set of
types that PostTc can return, but that isn't currently possible (see
http://hackage.haskell.org/trac/ghc/ticket/6074#comment:5
), and even if it was, it would be a few years before we could use it in
GHC.
> The build system resolves the directories in the GHC source tree, so I'm
> compensating for this by seeing which files I can find. To this end, I first
> build a name table by seeing what files I can find in the source tree:
I'm a little confused. Why aren't you just setting importPaths (like the
ghc -ifoo flag does)?
> The FIXME poses the problem. If I add the target, GHC panics when it comes to
> FastString.lhs, saying that "Data.Data" is a package module.
I didn't follow exactly what you're doing, but if ghci does it then it
can often be useful to look at how.
Thanks
Ian
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