[antlr-interest] tree parsers vs visitors & xml translators etc...

[Terence Parr]

Heh, just found a very good reason to use a tree grammar over a simple 
AST visitor or any other translator you'd find in the XML world: 
visitors have to look for your pattern over the whole tree whereas a 
tree grammar specifies precisely where to look and, most importantly, 
when to stop looking!  On large ASTs such as those representing Java 
programs this can be a big win.

For example, I'm working on the java parser / tree parser we have.  My 
first tree phase will pick up class/interface and method definitions.  
Naturally, these are all at the outermost layers within the Java ASTs 
and it would not make sense to look into every expression in your java 
program looking for class defs.  The tree parser knows these constructs 
exist at the highest level and therefore does not traverse all the 
expressions (I use '.' wildcard to terminate the walk when I know 
there's no hope of finding deeper class defs).

I'm guessing that most visitor patterns and all XSLT type stuff will 
search the whole damn tree looking for node of type CLASS_DEF.  
<snicker>.

Can anybody comment on the visitor/xslt side?  How would you do this 
"find class defs" problem efficiently?

Hooray for tree grammars!  And now back to your regularly scheduled 
lives...

Ter
--
Co-founder, http://www.jguru.com
Creator, ANTLR Parser Generator: http://www.antlr.org


 

Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/