I'm working with the tree pattern matching and think it is excellent
(especially re-writing).
I have repeatedly come across the need to match trees that are descents of
other sub-trees, but have not found an elegant way to do so.
For example...
Given the tree:
^(GROUP
^(UPDATE ^(SET RULE) ^(SET RULE))
^(UPDATE ^(SET RULE RULE ^(SET RULE RULE)) ^(SET RULE))
^(QUERY ^(SET RULE) ^(SET RULE RULE)))
I would like to match all RULE entries that are under an UPDATE but not a
QUERY.
I have come up with two solutions but I'm not happy with either and I'm
wondering if anybody else has a suggestion.
Solution #1: Specify the nesting path...
topdown: ^(UPDATE matchSet);
matchSet: ^(SET (matchRule | matchSet));
matchRule: RULE {...}
This requires enumerating all of the paths that a value COULD be at, so
things get really ugly if a SET can contain many types of items that can
also contain RULE entries.
Solution #2: Flag and filter
@members{boolean inUpdate = false;}
topdown
: ^(UPDATE .*) {inUpdate = true;}
| {inUpdate}?=> RULE -> ^(RULE NEW STUFF);
bottomup: ^(UPDATE .*) {inUPdate = false;}
The use of state makes a serialization point to flag when I am in a in my
otherwise nicely concurrent application, since there is now a global
variable of the parser called inUpdate.
This need is similar to recursive path operations in Apache Ant with **
specifier (at some depth below).
Is there a similar syntax for ANTLR contextual sub-tree matching?
Many thanks,
-Joseph A. Cottam
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