You're seeing just the function pop, go back to Ergo.Stack module for more information.

You cannot pop an element from an empty stack.

At this point it's not clear if this operation should raise an exception or return an error. For now we'll return an error.


iex> alias Ergo.Stack
iex> s =
iex> assert {:error, nil, []} = Stack.pop(s)
iex> s = s |> Stack.push(true) |> Stack.push(false)
iex> assert [false, true] = s
iex> assert {:ok, false, [true]} = Stack.pop(s)