Interpreted stack machines are very similar in concept to Reverse Polish notation.
The expression
3 + (6 - 2)
is expressed in RPN as
3 6 2 - +
This gets evaluated as follows:
Input Operation Stack Comment
3 Push value 3
6 Push value 6
3
2 Push value 2
6
3
- Subtract 4 Pop two values (6, 2) and push result (4)
3
+ Add 7 Pop two values (3, 4) and push result (7)
From there, it should be easy to build a simple interpreted stack machine in C#. E.g.
var stack = new Stack<int>();
var program = new[]
{
OpCode.Ldc_3,
OpCode.Ldc_6,
OpCode.Ldc_2,
OpCode.Sub,
OpCode.Add,
};
for (int i = 0; i < program.Length; i++)
{
int a, b;
switch (program[i])
{
case OpCode.Add: b = stack.Pop(); a = stack.Pop(); stack.Push(a + b); break;
case OpCode.Sub: b = stack.Pop(); a = stack.Pop(); stack.Push(a - b); break;
case OpCode.Mul: b = stack.Pop(); a = stack.Pop(); stack.Push(a * b); break;
case OpCode.Div: b = stack.Pop(); a = stack.Pop(); stack.Push(a / b); break;
case OpCode.Ldc_0: stack.Push(0); break;
case OpCode.Ldc_1: stack.Push(1); break;
case OpCode.Ldc_2: stack.Push(2); break;
case OpCode.Ldc_3: stack.Push(3); break;
case OpCode.Ldc_4: stack.Push(4); break;
case OpCode.Ldc_5: stack.Push(5); break;
case OpCode.Ldc_6: stack.Push(6); break;
case OpCode.Ldc_7: stack.Push(7); break;
case OpCode.Ldc_8: stack.Push(8); break;
}
}
var result = stack.Pop();
with
enum OpCode
{
Nop, // No operation is performed.
Add, // Adds two values and pushes the result onto the evaluation stack.
Sub, // Subtracts one value from another and pushes the result onto the
// evaluation stack.
Mul, // Multiplies two values and pushes the result on the evaluation
// stack.
Div, // Divides two values and pushes the result onto the evaluation
// stack.
Ldc_0, // Pushes the integer value of 0 onto the evaluation stack.
Ldc_1, // Pushes the integer value of 1 onto the evaluation stack.
Ldc_2, // Pushes the integer value of 2 onto the evaluation stack.
Ldc_3, // Pushes the integer value of 3 onto the evaluation stack.
Ldc_4, // Pushes the integer value of 4 onto the evaluation stack.
Ldc_5, // Pushes the integer value of 5 onto the evaluation stack.
Ldc_6, // Pushes the integer value of 6 onto the evaluation stack.
Ldc_7, // Pushes the integer value of 7 onto the evaluation stack.
Ldc_8, // Pushes the integer value of 8 onto the evaluation stack.
}
For a real world example, have a look at the fields of the OpCodes class in the .NET Framework.