Nested Boolean Expression Parser using ANTLR

[Sudhindra Kumar]

I'm new to ANTLR and I'm trying to parse a Nested Boolean Expression and get the individual conditions within the expression separately. For e.g., if the input string is:

(A = a OR B = b OR C = c AND ((D = d AND E = e) OR (F = f AND G = g)))

I would like to get the conditions with the correct order. i.e.,

D =d AND E = e OR F = f AND G = g AND A = a OR B = b OR C = c

I'm using ANTLR 4 to parse the input text and here's my grammar:

grammar SimpleBoolean;

rule_set : nestedCondition* EOF;

AND : 'AND' ;
OR  : 'OR' ;
NOT : 'NOT';

TRUE  : 'TRUE' ;
FALSE : 'FALSE' ;

GT : '>' ;
GE : '>=' ;
LT : '<' ;
LE : '<=' ;
EQ : '=' ;

LPAREN : '(' ;
RPAREN : ')' ;

DECIMAL : '-'?[0-9]+('.'[0-9]+)? ;

IDENTIFIER : [a-zA-Z_][a-zA-Z_0-9]* ;

WS : [ \r\t\u000C\n]+ -> skip;

nestedCondition : LPAREN condition+ RPAREN (binary nestedCondition)*;
condition: predicate (binary predicate)*
            | predicate (binary component)*;
component: predicate | multiAttrComp;
multiAttrComp : LPAREN predicate (and predicate)+ RPAREN;
predicate : IDENTIFIER comparator IDENTIFIER;
comparator : GT | GE | LT | LE | EQ ;
binary: AND | OR ;
unary: NOT;
and: AND;

And here's the Java Code that I'm using to parse it:

ANTLRInputStream inputStr = new ANTLRInputStream(input);
SimpleBooleanLexer lexer = new SimpleBooleanLexer(inputStr);
TokenStream tokens = new CommonTokenStream(lexer);
SimpleBooleanParser parser = new SimpleBooleanParser(tokens);
parser.getBuildParseTree();
ParseTree tree = parser.rule_set();
System.out.println(tree.toStringTree(parser));

The output is:

(rule_set (nestedCondition ( (condition (predicate A (comparator =) a) (binary OR) (component (predicate B (comparator =) b)) (binary OR) (component (predicate C (comparator =) c)) (binary AND) (component (multiAttrComp ( (predicate ( D (comparator =) d) (and AND) (predicate E (comparator =) e) ))) (binary OR) (component (multiAttrComp ( (predicate F (comparator =) f) (and AND) (predicate G (comparator =) g) )))) ) )) <EOF>)

I'm looking for help on how to parse this tree to get the conditions in the correct order? In ANTLR 3, we could specify ^ and ! to decide how the tree is built(refer this thread), but I learnt that this is not supported in ANTLR 4.

Can someone suggest how I can parse the String in the correct order?

[Jonathan Coveney]

Antlr4 can handle this and I believe the antlr4 book even has an example?

Either way, if you make an OR version of multiAttrcomp and put it in the right order, then in antlr4 the order defines the precedence. "it's that simple" (tm)

Here is an example: http://stackoverflow.com/questions/9509048/antlr-parser-for-and-or-logic-how-to-get-expressions-between-logic-operators

though this is actually more verbose than it needs to be with the new fancy pants precedence generation.

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