[antlr-interest] Building AST's for CSS2.1 with ANTLR

[Simon Janes]

(this was previously titled) Re: Interesting problem with ANTLR and
CSS 2.1 (tokens added to AST rewrites almost works)

You know, I tried that and for whatever reason, this still isn't
working for me and I suspect its the weirdness of CSS--has anyone
written a "best practice" for pulling AST's out of a parse tree with
ANTLR 3.0.1?   I've been reading the ANTRv3.g and Cpp.g grammars to
get some context.

* Do you always need to supply a token or literal token to be the
"root" or "parent" of a AST tree/subtree?

Simon

On 10/13/07, Austin Hastings <Austin_Hastings at yahoo.com> wrote:
> Simon,
>
> You're not asking for what you want. :)
>
> When you say
>
> parse : stylesheet* -> ^(STYLESHEET stylesheet) ;
>
> you are asking for only one stylesheet. When you are faced with a rule
> element that has a cardinality different from "exactly one" you need to
> use a cardinality operator on the right hand side of the -> as well.
>
> Try this:
>
> parse:  stylesheet* -> ^(STYLESHEET stylesheet*) ;
>
> Or for a weird time, try this:
>
> parse: stylesheet* -> ^(STYLESHEET stylesheet)* ;
>
> (Dump them both so you'll grok the difference.)
>
> This trick works with + as well. Sometimes you can use ? too, but I've
> occasionally had to use * on the RHS when I used ? on the left - this is
> 3.0.1 after all. :)
>
> =Austin
>
>
>
> Simon Janes wrote:
> > Thanks dave!
> >
> > That almost works-- now I no longer get the "more than one node as
> > root" error, but only receive one child in the list.  I got this by
> > changing the grammar rules here and introducing some "semantic"
> > tokens:
> >
> > ----
> > parse :       stylesheet* -> ^(STYLESHEET stylesheet);
> >
> > stylesheet
> >       : comment_stylesheet -> ^(COMMENT comment_stylesheet)
> >       | ruleset -> ^(RULESET ruleset)
> >       | media -> ^(MEDIA media)
> >       | page -> ^(PAGE page)
> >       ;
> > ----
> >
> > The CSS for this run:
> >
> > /* hello comment */
> > .hello { color: blue; font-face: Arial; }
> > .again { color: blue; }
> >
> > The getStringTree() dump:
> >
> > (STYLESHEET (COMMENT /* hello comment */))
> >
> > Is there something I need to do tell it to append to a node?
> >
> >
> >
> >> On Fri, Oct 12, 2007 at 04:23:04PM -0400, Simon Janes wrote:
> >>
> >>> parse    :    stylesheet -> ^(stylesheet); /* I think this sets the "root"
> >>> of the AST. */
> >>>
> >>> stylesheet
> >>>     : (comment_stylesheet|ruleset|media|page)* ;
> >>>
> >>> I'll get a runtime error:
> >>>
> >>> "more than one node as root"
> >>>
> >> I've not seen that before, but I assume the problem is that..
> >>
> >>   -> ^(stylesheet)
> >>
> >> ..attempts to make the AST referenced by 'stylesheet' be the root node of
> >> the result AST, but in your case 'stylesheet' does not represent a
> >> single node, but a list of nodes.
> >>
> >> Probably you should just remove the '^'..
> >>
> >>   parse    :    stylesheet -> stylesheet;
> >>
> >> ..but then you might as well just remove the rewrite, because it doesn't
> >> add anything..
> >>
> >>   parse    :    stylesheet;
> >>
> >>
> >> Alternatively, you could add an 'imaginary' node to act as the root, if
> >> you really want a single node result rather than a list..
> >>
> >>   parse    :    stylesheet -> ^(STYLESHEET stylesheet);
> >>
> >>
> >> Note that for the standard ANTLR tree implementation, a 'list' of nodes
> >> is really just a special case node:
> >>
> >>   http://www.antlr.org/api/Java/classorg_1_1antlr_1_1runtime_1_1tree_1_1_common_tree.html#670edeb282b219bc714ed9490aa5a728
> >>
> >>
> >> ta,
> >> dave
> >>
> >>
> >
> >
> >
>
>