[antlr-interest] working with AST

[mzukowski at yci.com]

tokens{
ALT1;
ALT2;
}

rule1: (test1)=> alt1 {##=#(#[ALT1], ##);}
       | alt2 {##=#(#[ALT2],##);}

This is a common idiom.  I use it all over the gcc grammar for instance.
http://www.codetransform.com/gcc.html

## means "the current tree"
#[ALT1] means create a new node with ALT1 as the type
#() means create a new tree with the nodes given

Monty

-----Original Message-----
From: Adrian Sandor [mailto:aditsu at yahoo.com] 
Sent: Saturday, July 19, 2003 6:36 AM
To: antlr-interest at yahoogroups.com
Subject: [antlr-interest] working with AST


I have a parser which builds an AST, and uses some syntactic predicates;
currently it's basically a list, it doesn't have levels, and when I parse
the AST for translation, I need to use similar predicates for correct
recognition I know I should create subtrees for easier processing, but the
only example I saw was for expressions where it was very easy to use the
operators as roots, but in my case I can't find any specific token to
identify the subtree uniquely is there any way to create and add
non-existing tokens as roots to mark certain kinds of subtrees?

e.g. I have:
rule1: (test1) => alt1 | alt2;

then I want to "label" the two alternatives, e.g. #(ALT1 alt1) and #(ALT2
alt2), where ALT1 and ALT2 did not exist in the lexer can I do that? or
something similar?

Adrian


 

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