static IElement Parse(IReadOnlyList <Token> tokens)
{
var result = new BinaryOperation();
bool haveLHS = false;
for (int i = 0; i < tokens.Count; i++)
{
var token = tokens[i];
switch (token.MyType)
{
case Token.Type.Integer:
var integer = new Integer(int.Parse(token.Text));
if (!haveLHS)
{
result.Left = integer;
haveLHS = true;
}
else
{
result.Right = integer;
}
break;
case Token.Type.Plus:
result.MyType = BinaryOperation.Type.Addition;
break;
case Token.Type.Minus:
result.MyType = BinaryOperation.Type.Subtraction;
break;
case Token.Type.Lparen:
int j = i;
for (; j < tokens.Count; ++j)
{
if (tokens[j].MyType == Token.Type.Rparen)
{
break;
}
}
var subexpression = tokens.Skip(i + 1).Take(j - i - 1).ToList();
var element = Parse(subexpression);
if (!haveLHS)
{
result.Left = element;
haveLHS = true;
}
else
{
result.Right = element;
}
i = j;
break;
default:
throw new ArgumentOutOfRangeException();
}
}
return(result);
}
public int Calculate(string expression)
{
var tokens = Lex(expression);
var lastToken = tokens[tokens.Count - 1];
if (lastToken.MyType == Token.Type.Unknown)
{
return(0);
}
var result = new BinaryOperation();
bool haveLHS = false;
for (int i = 0; i < tokens.Count; i++)
{
var token = tokens[i];
switch (token.MyType)
{
case Token.Type.Integer:
var integer = new Integer(int.Parse(token.Text));
if (!haveLHS)
{
result.Left = integer;
haveLHS = true;
}
else
{
result.Right = integer;
if (i < tokens.Count - 1)
{
result.Left = new BinaryOperation
{
Left = result.Left,
Right = result.Right,
OperationType = result.OperationType
};
}
}
break;
case Token.Type.Plus:
result.OperationType = BinaryOperation.Type.Addition;
break;
case Token.Type.Minus:
result.OperationType = BinaryOperation.Type.Subtraction;
break;
}
}
return(result.Value);
}
