A couple of GHC-API questions

Simon Peyton Jones simonpj at microsoft.com
Thu Jul 24 07:32:23 UTC 2014


I'd like to help but I don't understand the question.  What do you mean by "resolve" all the types that are imported from module A?  

If you have a TyCon (for A.Foo) in your hand, it has a Name. That Name tells you where it comes from. Inside it you will find its DataCons which also come from A.  And so on.

Later you say "is there a simple way to ask GHC to resolve the name x in the context of module m".  You could mean
 * Imagine that the unqualified name "x" appeared in module m.  How do I look it up, in m's top-level lexical environment.
but I don’t think that is what you mean.

I'm confused. Could you be more concrete?
Possibly this may help? https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/NameType

I'm cc'ing ghc-devs.  


| -----Original Message-----
| From: Eric Seidel [mailto:eseidel at cs.ucsd.edu]
| Sent: 23 July 2014 19:01
| To: Simon Peyton Jones
| Subject: A couple of GHC-API questions
| Hi Simon,
| I have a couple of questions about how to use GHC’s API properly.
| There’s nothing urgent here as we’re making due just fine in
| LiquidHaskell, but I’m pretty sure we’re hacking around GHC when we
| don’t need to :)
| As you probably know, we basically use GHC to get the Core binders of a
| module, and to resolve a bunch of names. Translating to Core has never
| been an issue for us as far as I know, but our name-resolution code is
| very haphazard. The core of our problems with name-resolution comes
| down to resolving the names in specifications that have been imported
| from another module, e.g.
|     module A where
|     data Foo
|     mkFoo :: {v:Int | v >= 0} -> Foo
|     ...
|     module B where
|     import qualified A
|     ...
| When we verify module B we have to first resolve all of the types that
| were imported from module A, *but* we can’t do that in the context of
| module B due to the qualified import. So I’ve been using a slightly
| modified version of GHC’s DynamicLoading.lookupRdrNameInModule to
| handle the change of context, but this seems to require that we use the
| HscInterpreted flag, which causes further problems for a few of our
| benchmarks that make use of the C FFI.. This method also only works for
| modules where we actually have the source code available, i.e. we have
| to use a different method of looking up names to attach specifications
| to functions from the base libraries.
| So I guess my question is this: is there a simple way to ask GHC to
| resolve the name x in the context of module m, without invoking the
| code generator or any other part of GHC’s functionality? I suppose a
| more principled solution would be to somehow hook into the .hi files
| that GHC generates, but I’m not sure if that’s possible.
| Again, the code we have right now works, it’s just very fragile and I’d
| like to clean things up.
| Thanks!
| Eric

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