I agree that
additiveExpression
: multiplicativeExpression ('+' | '-') multiplicativeExpression
| multiplicativeExpression
;
is equiwalent to:
additiveExpression
: multiplicativeExpression (('+' | '-') multiplicativeExpression)?
;
Why it does not generate the same AST tree I do not know. May be it is a bug - I have to investigate.
Goot point about the "a + b + c" case.
Thanks,
Tomasz
--- On Fri, 8/7/09, Sam Barnett-Cormack <s.barnett-cormack at lancaster.ac.uk> wrote:
From: Sam Barnett-Cormack <s.barnett-cormack at lancaster.ac.uk>
Subject: Re: [antlr-interest] could not even do k=1 for decision xx; reason: timed out
To: "Tomasz Jastrzebski" <tdjastrzebski at yahoo.com>
Cc: "antlr-interest" <antlr-interest at antlr.org>
Date: Friday, August 7, 2009, 6:29 PM
Tomasz Jastrzebski wrote:
> But this creates a different tree, while what I need is plain and simple structure like this:
> +
> / \
> / \
> a *
> / \
> / \
> c d
No, it does exactly what the one you provided does. The output rule is only observed if the subrule matches, otherwise it follows the default. It is identical in effect to the rule you provided...
additiveExpression
: e1=multiplicativeExpression ((o='+'|o='-')
e2=multiplicativeExpression ->
BINARY_EXPRESSION<BinaryExpression>[$o.text, $e1.tree, $e2.tree])?
;
(I've corrected where it should be a question mark, not * - * would accept chained expressions, but the tree rewrite would be awkward)
If the subrule matches, the rewrite (which I don't quite understand) applies. If it doesn't, then the default (just emit the token as a single node) takes place.
Your grammar doesn't appear to support expressions like
3 + 4 - 5
or
2 * 3 / 5
Sam
> --- On *Fri, 8/7/09, Sam Barnett-Cormack /<s.barnett-cormack at lancaster.ac.uk>/* wrote:
>
>
> From: Sam Barnett-Cormack <s.barnett-cormack at lancaster.ac.uk>
> Subject: Re: [antlr-interest] could not even do k=1 for decision xx;
> reason: timed out
> To: "Tomasz Jastrzebski" <tdjastrzebski at yahoo.com>
> Date: Friday, August 7, 2009, 2:30 PM
>
> Tomasz Jastrzebski wrote:
>
> > But the problem is that I cannot do that since I need to catch
> reference to each expression and operator to build nice AST tree.
> The real code looks more like this:
> > additiveExpression
> > : e1=multiplicativeExpression (o='+' | o='-')
> e2=multiplicativeExpression ->
> BINARY_EXPRESSION<BinaryExpression>[$o.text, $e1.tree, $e2.tree]
> > | multiplicativeExpression
> > ;
>
> Still left-factor it.
>
> additiveExpression
> : e1=multiplicativeExpression ((o='+'|o='-')
> e2=multiplicativeExpression ->
> BINARY_EXPRESSION<BinaryExpression>[$o.text, $e1.tree, $e2.tree])*
> ;
>
> This means that the output expression is only considered if the
> optional subrule matches - otherwise it uses the default output
> (just e1).
>
> -- Sam Barnett-Cormack
>
>
-- Sam Barnett-Cormack
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