FYI it's #7828, not #7282.

Jan, I'm very glad you're working on this. Thanks!

On Mon, Jun 16, 2014 at 2:33 PM, Jan Stolarek <jan.stolarek@p.lodz.pl> wrote:

> Why do you want this? The danger I see lurking is that you might find two
> RdrNames that give the same answer to getUnique but represent different

Yes, that's exactly my concern.

> Why do you want this?

I'm working on #7282 - RebindableSyntax and Arrows. Here's a snippet from desugaring of arrow
notation:

leaves = concatMap leavesMatch matches
 where
   leavesMatch :: LMatch Id (Located (body Id)) -> [(Located (body Id), IdSet)]
   leavesMatch (L _ (Match pats _ (GRHSs grhss binds)))
         = let defined_vars = mkVarSet (collectPatsBinders pats) `unionVarSet`
                                          mkVarSet (collectLocalBinders binds)
             in  [(body, mkVarSet (collectLStmtsBinders stmts) `unionVarSet` defined_vars) | L _
(GRHS stmts body) <- grhss]

This is in the desugarer. But I need to also know `length leaves` at the renaming stage, which
means I need to call `concatMap leavesMatch matches`. The problem is that in the renamer my
datatypes are not parametrised by `Id`. I turned `Id` into a type parameter `id`, but then I
can't use VarSets. I could use more general UniqueSets but only if `id` type parameter is an
instance of Uniquable. And since in the renamer the datatypes are parametrized with RdrName this
leads me to wanting Uniqable RdrName instance.

Janek
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