immutablestack

type Functor func(interface{}) interface{}

type ImmutableStack interface {
	// Top returns the top element on the stack.
	Top() interface{}

	// Pop returns the next substack.
	Pop() ImmutableStack

	// Size returns the size of the stack.
	Size() uint64

	// Push pushes a new element onto the stack and returns a new stack.
	Push(interface{}) ImmutableStack

	// ForEach iterates over the stack and applies the iterator function to each
	// substack until it finds the empty one or the iterator returns an error.
	ForEach(Iterator)

	// FMap applies a function to each element on the stack and returns the new
	// stack with results of the function application.
	FMap(f Functor) ImmutableStack
}

type Iterator func(ImmutableStack) error