[antlr-interest] Inserting missing nodes

Jean-Sebastien Vachon jean-sebastien.vachon at wantedtech.com
Thu Apr 28 13:06:33 PDT 2011


Hi All,

First, I'd like to make it clear that I'm new to ANTLR so please be kind with me ;)

Second, my main problem right now is that I'm currently building a grammar that will let
me validate and parse a Boolean query with some special features. I got 90% of my parser working but I'm stuck with the last
feature that is required. Basically, I need to be able to insert missing operators (AND/OR) where required.

Considering the following query: "software engineer java"
I need to build a tree representing the query as if it was "software AND engineer AND java" but I also need to be able to change the inserted operator 'AND' to something else.

My first thought was to push a new type of node (let's say DEFAULT_OP) into my tree using a rewrite rule that I could rewrite to the proper operator using a tree walker and/or translator.

I made a few tries and got it working in some situations but I can't get it to parse everything I'm throwing at it. My best try so far is shown in the listing below... I did not include the lexer as it is pretty straight forward...

All hints and comments are welcomed...

Thanks for your help
===============================
grammar MyGrammar;

options {
  language = Java;
  output = AST;
  ASTLabelType = CommonTree;
}

query
  : and_expr+ EOF!
  ;

and_expr
  : (expr expr+) => default_op
  | (u1=or_expr (AND^ u2=or_expr)*);

or_expr
  : u1=expr (OR^ u2=expr)*
  ;

default_op
  : (e1=or_expr e2=or_expr) -> ^(DEFAULT_OP $e1 $e2)
  ;

expr
  : (NOT^)? (operand)
  ;

operand
  : (FIELD^)(operand)
  | PREFIX
  | WORD
  | SENTENCE
  | WORDLIST
  | NEGATIVE(w=PREFIX|w=WORD|w=SENTENCE|w=WORDLIST) -> ^(NOT $w)
  | MUST
  | LPAREN! expr RPAREN!
  ;



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