Tail recursion is recursion in which the recursive call is the function's final operation. The compiler can implement that call as a jump rather than allocating another stack frame, so the function consumes no additional memory during iteration. section 3.4.2
This makes tail recursion suitable for loops that may run arbitrarily long. In Elixir, recursion supplies the loop, while function clauses handle the terminating and continuing cases. section 3.4.2 section 3.5
A practical tail-recursive design typically separates the public interface from the accumulator-driven recursion:
- Expose a simple function such as sum/1. section 3.4.2
- Delegate to a private helper carrying the accumulated result. section 3.4.2
- Match the empty input and return the accumulator. section 3.4.2
- Compute the next accumulator and make the recursive call last. section 3.4.2
Tail-recursive list sum
ListHelper.sum([1, 2, 3]) returns 6, while ListHelper.sum([]) returns 0. The helper advances through the list with current_sum and tail, then returns the accumulated value when the list is empty. section 3.4.2
Listing 3.9 Tail-recursive sum of the first n natural numbers (sum_list_tc.ex)
defmodule ListHelper do def sum(list) do do_sum(0, list) end defp do_sum(current_sum, []) do current_sum end defp do_sum(current_sum, [head | tail]) do new_sum = head + current_sum do_sum(new_sum, tail) end end
Inspect the complete Elixir implementation, including the public wrapper, accumulator, pattern-matching clauses, and terminating case. section 3.4.2
