entity example is
  generic (
    RECURSION_DEPTH : natural);
end example;


architecture rtl of example is

  ------------------------------------------------------------------------------
  -- Function declarations
  ------------------------------------------------------------------------------
  function function_1 (
    constant RECURSION_DEPTH : natural)
    return natural;

  function function_2 (
    constant RECURSION_DEPTH : natural)
    return natural;


  ------------------------------------------------------------------------------
  -- Function definitions
  ------------------------------------------------------------------------------
  function function_1 (
    constant RECURSION_DEPTH : natural)
    return natural is
  begin
    if (RECURSION_DEPTH > 0) then
      return
        function_2(
          RECURSION_DEPTH => RECURSION_DEPTH-1);
    else
      return 0;
    end if;
  end function_1;

  function function_2 (
    constant RECURSION_DEPTH : natural)
    return natural is
    variable retval : natural;
  begin

    retval :=
      function_1(
        RECURSION_DEPTH => RECURSION_DEPTH);

    return retval;
  end function_2;


  ------------------------------------------------------------------------------
  -- Function call
  ------------------------------------------------------------------------------
  constant retval : natural :=
    function_1(
      RECURSION_DEPTH => RECURSION_DEPTH);

begin
end rtl;