N-th Fibonacci number in ABAP using a recursive Function Module (not memoized yet!!)

z_nth_fibo_number.abap

FUNCTION z_nth_fibo_number.
*"----------------------------------------------------------------------
*"*"Local Interface:
*"  IMPORTING
*"     VALUE(IV_INDEX) TYPE  I
*"  EXPORTING
*"     VALUE(EV_FIBO_NUMBER) TYPE  I
*"  EXCEPTIONS
*"      INDEX_LOWER_THAN_ZERO
*"----------------------------------------------------------------------
*  Returns a Fibonacci number on n-th index.
*  Given 1, 1, 2, 3, 5, 8, 13, 21, ...
*   The result is 5 if n = 5.
*   The result is 21 if n = 8.
*----------------------------------------------------------------------
*  Author: Boghyon Hoffmann
*  TODO: Memoize this function to avoid repeating same calculations for which the results have been already submitted before.
*----------------------------------------------------------------------.

  IF iv_index < 0. "exception handling
    RAISE index_lower_than_zero.
  ELSE. "calculate the result
    DATA(index_substracted1) = iv_index - 1.
    DATA(index_substracted2) = iv_index - 2.

    IF iv_index LE 2.
      ev_fibo_number = 1.
    ELSE.
      DATA(result1) = 0.
      CALL FUNCTION 'Z_NTH_FIBO_NUMBER'
        EXPORTING
          iv_index       = index_substracted1
        IMPORTING
          ev_fibo_number = result1.

      DATA(result2) = 0.
      CALL FUNCTION 'Z_NTH_FIBO_NUMBER'
        EXPORTING
          iv_index       = index_substracted2
        IMPORTING
          ev_fibo_number = result2.

      ev_fibo_number = result1 + result2. "return
    ENDIF.
  ENDIF.
ENDFUNCTION.