Special treatment of family and role in the parser
thomasmiedema at gmail.com
Wed Jan 20 20:10:17 UTC 2016
CC Ulya Trofimovich (skvadrik), who removed the remaining reduce/reduce
conflicts from the parser last year, and can maybe also help out here.
Ulya: see email from Jan below.
On Wed, Jan 20, 2016 at 8:25 PM, Richard Eisenberg <eir at cis.upenn.edu>
> From your email, you understand everything I do about this. :)
> I think the challenge really is just understanding and eliminating these
> conflicts. See the commentary at the top of Parser.y to see how to get an
> analysis of the conflicts.
> While you're in the area, you may want to look at #11267. It's not quite
> related, but it's also about parsing types.
> On Jan 20, 2016, at 1:42 PM, Jan Stolarek <jan.stolarek at p.lodz.pl> wrote:
> > Richard, I still don't fully understand special treatment of 'role' and
> 'family' in the parser I
> > asked about recently on Skype. Say I have:
> > foo :: role -> role
> > foo role = role
> > This results in parse error of type signature, regardless of enabling or
> > disabling -XRoleAnnotations. Using `role` as a variable name (not type
> variable) is fine though.
> > This is a consequence of explicitly listing 'role' lexeme in the varid
> production in the parser,
> > but not in tyvarid production. But if I add 'role' to tyvarid production
> (or, even better, push
> > it to special_id production used both by varid and tyvarid) everything
> works perfectly, I can use
> > `role` both as variable and type variable name. Role annotations also
> work. The only downside is
> > a small increase in number of shift/reduce conflicts. If I treat
> 'family' in the same way (ie.
> > add it to tyvarid production) the increase in shift/reduce conflicts
> really becomes significant:
> > from 37 to 129. Is this the only reason we don't do it? As you can guess
> this question is related
> > to open kinds work: I need to add 'kind' lexeme to special_id to make
> sure it is accepted as a
> > variable and type variable name.
> > Janek
> > ---
> > Politechnika Łódzka
> > Lodz University of Technology
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