final Matcher identifierMatcher = identifierPattern.matcher(expression.substring(position));
if (identifierMatcher.lookingAt()) {
String identifierPart = identifierMatcher.group(1);
if (!identifierPart.isEmpty()) {
if (keywords.contains(identifierPart)) {
tokens.add(new KeywordToken(position, identifierPart));
} else {
tokens.add(new IdentifierToken(position, identifierPart));
}
position += identifierPart.length();