[antlr-interest] Multiple pass tree walking Q

[Paul Johnson]

Hill, Robert wrote:
> I've pretty much gone down the multiple tree parser routes, its a real 
> pain in the ass though, as if you modify your parser, you then have to 
> modify all the tree parser grammars too. I must be missing something 
> here. :(
> there must be a rule that ignores a whole branch, but i've tried all 
> sorts and haven't succeeded ,
>  
> ignoreme : ^(.*) ... if only :)
>  
> which is why i ended up with 3 tree parse phases. I just get this 
> nagging feeling im missing the point.

You won't like this reply, but this is why I don't use tree grammars. 
I've got 8 passes, each of which needs to modify the AST. I manually 
parse the tree, and cut out branches when I've finished with them (or 
replace nodes, or whatever).

The recursive tree parse in each pass is (almost) trivial, so a grammar 
would buy me little. I do have occasional complications with having to 
find my context in the tree, parsing node lists right-to-left instead of 
left-to-right, and so on, but no major problems, and certainly nothing 
that would justify maintaining 8 different grammars. One major advantage 
is that I can trivially add extra passes that do almost nothing, except 
maybe some cleaning up for the next pass.

Disclaimer: I've never actually tried the tree grammar route, so I (too) 
may have missed easy ways to do what I'm now doing manually.

There's a lot on this in the archives - have a look. You could start 
with Andy Tripp's reply in the "How much use is ANTLR for manipulating 
ASTs?" thread (18/06/2005).

Paul