Implement runtime stack for Stack-VM

stack.rs

pub struct VMStack {
    internal_stack: Vec<i32>,
    capacity: usize,
    top: usize, //also size
}

impl VMStack {
    pub fn new(stack_size: usize) -> VMStack {
        VMStack { capacity: stack_size, top: 0, internal_stack: Vec::with_capacity(stack_size) }
    }

    pub fn push(&mut self, data: i32) {
        if self.top == self.capacity {
            panic!("Stack overflow Capacity {} , Size {} ", self.capacity, self.top)
        }
        self.internal_stack.push(data);
        self.top += 1;
    }

    pub fn pop(&mut self) -> i32 {

        if self.top == 0 {
            panic!("Stack underflow")
        }
        self.top-=1;
        self.internal_stack.pop().unwrap()
    }
}