Uniquable RdrName instance

Simon Peyton Jones simonpj at microsoft.com
Tue Jun 17 16:00:17 UTC 2014

We just haven't needed one so far.

Can a RdrName and a Name have the same Unique?  Well, of course that just depends on what you are using the RdrName Uniques for.  It's not a question that has a yes or no answer.

Does it matter if (Orig m x) and (Orig n x) have the same Unique? Same answer, except that I bet the answer is "yes it matters". 

FWIW the "OrigNameCache" is a finite map keyed by (ModuleName,Orig) pairs.


| -----Original Message-----
| From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Jan
| Stolarek
| Sent: 16 June 2014 12:45
| To: ghc-devs at haskell.org
| Subject: Uniquable RdrName instance
| Hi all,
| I just found myself in the need of Uniquable instance for RdrName. I'm
| surprised that such instance does not exist already because other
| datatypes like Name or OccName already have Uniquable instances. So, is
| there a reason why Uniquable instance for RdrName does not exist already
| (other than "it wasn't needed")? How should such an instance look like?
| I made an
| attempt:
| rdrNameUnique :: RdrName -> Unique
| rdrNameUnique (Unqual occName) = getUnique occName rdrNameUnique (Qual _
| occName) = getUnique occName rdrNameUnique (Orig _ occName) = getUnique
| occName
| rdrNameUnique (Exact name    ) = getUnique name
| But I suspect this might be wrong:
| - cases 1 and 4 simply return a Unique for the OccName/Name stored
| inside RdrName. I think this will assign the same Unique to RdrName and
| corresponding OccName/Name. Is this allowed?
| - cases 2 and 3 ignore the Module stored inside RdrName. Again, this
| assigns the RdrName with a Unique identical to OccNames stored inside
| it.
| Help appreciated.
| Janek
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