fix Parser::parseAnyOperator silently ignoring errors

libwccl/parser/Parser.cpp

@@ -135,11 +135,11 @@ boost::shared_ptr<ANTLRParserResultBase> Parser::parseAnyOperator(
 boost::shared_ptr<ANTLRParserResultBase> Parser::parseAnyOperator(
 		std::istream& istr) const
 {
-	ANTLRLexer lexer(istr);
-	ANTLRParser parser(lexer);
-
 	boost::shared_ptr<ANTLRParserResultBase> result;
 	if (!result) {
+		istr.seekg(0, std::ios::beg);
+		ANTLRLexer lexer(istr);
+		ANTLRParser parser(lexer);
 		try {
 			result = parser.parse_sym_set_operator(this->tagset);
 		} catch (antlr::ANTLRException) {
@@ -147,6 +147,9 @@ boost::shared_ptr<ANTLRParserResultBase> Parser::parseAnyOperator(
 		}
 	}
 	if (!result) {
+		istr.seekg(0, std::ios::beg);
+		ANTLRLexer lexer(istr);
+		ANTLRParser parser(lexer);
 		try {
 			result = parser.parse_string_operator(this->tagset);
 		} catch (antlr::ANTLRException) {
@@ -154,6 +157,9 @@ boost::shared_ptr<ANTLRParserResultBase> Parser::parseAnyOperator(
 		}
 	}
 	if (!result) {
+		istr.seekg(0, std::ios::beg);
+		ANTLRLexer lexer(istr);
+		ANTLRParser parser(lexer);
 		try {
 			result = parser.parse_predicates(this->tagset);
 		} catch (antlr::ANTLRException) {