// precedence-climbing method
// https://en.wikipedia.org/wiki/Operator-precedence_parser#Precedence_climbing_method
private Node parseExpression(Node lhs, int minPrecedence)
{
spyScannerToken();
// the spied token is an operator and has precedence >= the minimumum precedence
while (isOperator(spiedScannerToken.GetValueOrDefault()) && OPERATOR_PRECEDENCE[spiedScannerToken.GetValueOrDefault()].precedence >= minPrecedence)
{
GingerToken op = spiedScannerToken.GetValueOrDefault();
// move to spied position
nextScannerToken();
nextScannerToken();
Node rhs = parseTerminalExpression();
spyScannerToken();
// the spied token is an operator, and its precedence is greater than the previous op's precedence OR it is a right associated operator with precedence equal to op's precedence
while (isOperator(spiedScannerToken.GetValueOrDefault()) && (OPERATOR_PRECEDENCE[spiedScannerToken.GetValueOrDefault()].precedence > OPERATOR_PRECEDENCE[op].precedence || (OPERATOR_PRECEDENCE[spiedScannerToken.GetValueOrDefault()].rightAssociated && OPERATOR_PRECEDENCE[spiedScannerToken.GetValueOrDefault()].precedence == OPERATOR_PRECEDENCE[op].precedence)))
{
rhs = parseExpression(rhs, OPERATOR_PRECEDENCE[spiedScannerToken.GetValueOrDefault()].precedence);
spyScannerToken();
}
if (Grammar.isBinaryOperator(op))
{
lhs = new BinaryOperation(op, lhs, rhs);
}
else if (Grammar.isConditionOperator(op))
{
lhs = new InequalityOperation(op, lhs, rhs);
}
else
{
throw new ParseException(scanner.row, scanner.col, $"Expected '{GingerToken.Addition.ToString()}', or '{GingerToken.LessThan.ToString()}', found '{currentScannerToken.ToString()}'", ExceptionLevel.ERROR);
}
}
return lhs;
}
public void visitInequalityOperation(InequalityOperation c)
{
return;
}
public Inequality(int amount, InequalityOperation operation)
{
Amount = amount;
Operation = operation;
}
