My parser rules are listed as stmt : (elem|LPAREN stmt RPAREN) ( bop (elem| LPAREN stmt RPAREN) )* ; elem : "ti" WROD; bop : "and"|"or"|"not" ; WORD : ('a'..'z')+ ; LPAREN : '(' ; RPAREN : ')' ; However, when I parser "ti abc and ti efg", it complains with " unexpected token: null", I guess the lexer returned a null token to the parser at the end of the string and the parser still tried to mathch "any" based on the wildcard pattern. Any idea to resolve that. ( If I try to parser "ti abd and (ti efg)", it works fine. )    More>>

			

			stmt : (elem|LPAREN stmt RPAREN)
			

			( bop (elem| LPAREN stmt RPAREN) )*
			

			;
			

			

			elem : "ti" WROD;
			

			

			bop  : "and"|"or"|"not"
			

			;
			

			

			WORD : ('a'..'z')+
			

			;
			

			

			LPAREN : '('
			

			;
			

			

			RPAREN : ')'
			

			;