public void One_Plus_One_Should_Evaluate_To_Two()
{
var expression = new OperationExpression(
new ParameterExpression(1.0d),
Operand.Plus,
new ParameterExpression(1.0d));
var result = expression.Evaluate();
result.Should().Be(2d);
}
public IExpression Parse()
{
var left = new Stack<IExpression>();
var operands = new Stack<Operand>();
var right = new Stack<IExpression>();
while (HasMoreChars)
{
var c = _expression.Peek();
if (char.IsDigit(c))
{
var parameter = ReadParameterExpression();
var expression = ParseParameterExpression(parameter);
if (left.Count == right.Count)
{
left.Push(expression);
}
else
{
right.Push(expression);
}
}
else if (IsOperand(c))
{
var operand = ParseOperand(_expression.Pop());
if (right.Any() && (operand == Operand.Divide || operand == Operand.Multiply))
{
left.Push(right.Pop());
}
while (operands.Any() && left.Any() && right.Any())
{
var expression = new OperationExpression(left.Pop(), operands.Pop(), right.Pop());
if (left.Count == right.Count)
{
left.Push(expression);
}
else
{
right.Push(expression);
}
}
operands.Push(operand);
}
else if (IsOpeningBracket(c))
{
_expression.Pop();
var expression = Parse();
if (left.Count == right.Count)
{
left.Push(expression);
}
else
{
right.Push(expression);
}
}
else if (IsClosingBracket(c))
{
_expression.Pop();
while (operands.Any())
{
var expression = new OperationExpression(left.Pop(), operands.Pop(), right.Pop());
if (left.Count == right.Count)
{
left.Push(expression);
}
else
{
right.Push(expression);
}
}
return left.Pop();
}
else if (char.IsWhiteSpace(c))
{
_expression.Pop();
}
else
{
throw new NotImplementedException($"Cannot parse char '{c}'");
}
}
while (operands.Any())
{
var expression = new OperationExpression(left.Pop(), operands.Pop(), right.Pop());
if (left.Count == right.Count)
{
left.Push(expression);
}
else
{
right.Push(expression);
}
}
return left.Pop();
}