prosper/stack.go

package main

import "fmt"

// ErrEmpty denotes an empty stack
var ErrEmpty = fmt.Errorf("stack empty")

// ErrUnderflow denotes a PICK that tried to pick a value that didn't exist
var ErrUnderflow = fmt.Errorf("cannot pick value from beyond stack depth")

// Stack is a stack of integers with no defined max depth
type Stack struct {
	values []int
}

// Pop returns the top of the stack
func (s *Stack) Pop() (int, error) {
	if len(s.values) == 0 {
		return 0, ErrEmpty
	}
	i := s.values[0]
	s.values = s.values[1:]
	return i, nil
}

// Push adds a value to the top of the stack
func (s *Stack) Push(i int) {
	s.values = append([]int{i}, s.values...)
}

// Pick grabs a value from the given depth in the stack, non-destructively.
func (s *Stack) Pick(i int) (int, error) {
	if len(s.values) <= i {
		return 0, ErrUnderflow
	}
	return s.values[i], nil
}