static Expression ParseAdditiveExpression(Lexer lexer)
{
var rp = lexer.CreateRestorePoint();
var left = ParseMultiplicativeExpression(lexer);
if (left == null)
{
return null;
}
var type = lexer.CurrentToken.Type;
switch (type)
{
case TokenType.Plus:
case TokenType.Dash:
break;
default:
return left;
}
if (!lexer.Next())
{
rp();
return null;
}
var right = ParseAdditiveExpression(lexer);
if (right == null)
{
rp();
return null;
}
BinaryExpression result;
switch (type)
{
case TokenType.Plus:
result = new BinaryExpression(left, right, BinaryOperator.Addition);
break;
case TokenType.Dash:
result = new BinaryExpression(left, right, BinaryOperator.Subtraction);
break;
default:
result = null;
break;
}
return result;
}
public void Visit(BinaryExpression e)
{
var result = (Number)0m;
var right = _results.Pop();
var left = _results.Pop();
switch (e.Operator)
{
case BinaryOperator.Addition:
result = left + right;
break;
case BinaryOperator.Subtraction:
result = left - right;
break;
case BinaryOperator.Multiplication:
result = left * right;
break;
case BinaryOperator.Division:
result = left / right;
break;
}
_results.Push(result);
}