Uniquable RdrName instance

[Nicolas Frisby]

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 at 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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