Accessing the "original" names via GHC API

[Edward Z. Yang]

Hi Ranjit,

Unfortunately you need more information to do this, since the
set of modules which are available for import can vary depending
on whether or not packages are hidden or not (not even counting
whether or not a module is exposed or not!)

The way GHC's pretty printer gives a good name is that it keeps
track of all of the names in scope and where they came from
in a GlobalRdrEnv.  The relevant code is in 'mkPrintUnqualified'
in HscTypes, but if you pretty print using user-style with
an appropriately set up GlobalRdrEnv you should
get the things you want.

Edward

Excerpts from Ranjit Jhala's message of 2017-01-24 19:00:05 -0800:
> Dear Joachim,
> 
> You are right -- some more context.
> 
> Given
> 
>   tc  :: TyCon
>   m   :: ModName
>   env :: HscEnv
> 
> I want to get a
> 
>   s :: String
> 
> such that _in_ the context given by `m` and `env` I can resolve `s` to get
> back the original `TyCon`, e.g. something like
> 
>   L _ rn <- hscParseIdentifier env s
>   name   <- lookupRdrName env modName rn
> 
> would then return `name :: Name` which corresponds to the original `TyCon`.
> 
> That is, the goal is _not_ pretty printing, but "serialization" into a
> String
> representation that lets me recover the original `TyCon` later.
> 
> (Consequently, `"Data.Set.Base.Set"` doesn't work as the `Data.Set.Base`
> module is hidden and hence, when I try the above, GHC complains that the
> name is not in scope.
> 
> Does that clarify the problem?
> 
> Thanks!
> 
> - Ranjit.
> 
> 
> On Tue, Jan 24, 2017 at 6:11 PM, Joachim Breitner <mail at joachim-breitner.de>
> wrote:
> 
> > Hi Ranjit,
> >
> > Am Dienstag, den 24.01.2017, 16:09 -0800 schrieb Ranjit Jhala:
> > > My goal is to write a function
> > >
> > >    tyconString :: TyCon -> String
> > >
> > > (perhaps with extra parameters) such that given the
> > > `TyCon` corresponding to `Set`, I get back the "original"
> > > name `S.Set`, or even `Data.Set.Set`.
> > >
> > > Everything I've tried, which is fiddling with different variants of
> > > `PprStyle`, end up giving me `Data.Set.Base.Set`
> > >
> > > Does anyone have a suggestion for how to proceed?
> >
> > in a way, `Data.Set.Base.Set` is the “original”, proper name for Set,
> > everything else is just a local view on the name.
> >
> > So, are you maybe looking for a way to get the “most natural way” to
> > print a name in a certain module context?
> >
> > This functionality must exist somewhere, as ghci is printing out errors
> > this way. But it certainly would require an additional argument to
> > tyconString, to specify in which module to print the name.
> >
> > Greetings,
> > Joachim
> >
> >
> > --
> > Joachim “nomeata” Breitner
> >   mail at joachim-breitner.de • https://www.joachim-breitner.de/
> >   XMPP: nomeata at joachim-breitner.de • OpenPGP-Key: 0xF0FBF51F
> >   Debian Developer: nomeata at debian.org
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> >
> >