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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