[antlr-interest] Tricky tree rewrite without wildcards for subtree roots
Jim Idle
jimi at temporal-wave.com
Wed Apr 28 08:29:30 PDT 2010
Well, you cannot use . as the root as that will just match everything, but in fact your root is D anyway, so wall you need is something akin to:
tree grammar T;
options
{
output=AST;
}
a : x EOF ;
x : ^(A B C ^(D c+=x))
| .
;
With the rewrite rules added. This assumes that your representation below is accurate of course. Here you should then rewrite subtrees of D that are subtrees of A, in a recursive fashion.
Jim
> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Sebastian Bächle
> Sent: Wednesday, April 28, 2010 1:19 AM
> To: antlr-interest at antlr.org
> Subject: [antlr-interest] Tricky tree rewrite without wildcards for
> subtree roots
>
> Hi,
>
> I want to rewrite a subtrees of the form
>
> \
> A
> / | \
> / | \
> B C D
> / \
> E...F
>
> to
>
> \
> D
> / \ \
> A \ \
> / \ \ \
> B C E...F
>
>
> The problem is that D may be the subtree of an "arbitrary complex"
> expression
> that I don't know in advance - and I don't want to know. I am just
> interested
> in the surrounding construct defined by A, B, and C and want to become
> them
> the first child subtree of D, which itself takes over the place of its
> former
> parent A in the resulting tree.
>
> Is there a smart way to to do this with tree rewrite rules of antlr
> 3.2? Or
> must I manually modify the tree?
>
> I can think of a tree pattern rule similar to this
>
> ^(a=A b=B c=C ^(d=. children+=.*)) -> ^({$d.token} ^($a $b $c)
> $children+)
>
> but this is rejected with the error:
>
> Wildcard invalid as root; wildcard can itself be a tree
>
> I found a discussion from 2008 in the archives ("wildcard in tree
> grammar")
> about that particular topic. The design decision was to interpret "."
> in a
> tree grammar always as a whole subtree, forbidding constructs like the
> one
> above. As far as I understood, the underyling mechanism with
> interleaved
> UP/DOWN tokens for tree grammars, however, is potentially capable to
> match
> such wildcard patterns.
>
> I appreciate your hints and comments.
>
>
> Regards,
>
> Sebastian
>
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