[Oberon] Recursion of inner procedures

[August Karlstrom]

> On 2023-12-12 23:30, Diego Sardina wrote:
> Recently I wrote to Wirth about this and he confirmed that inner 
> procedures can call themselves. 
 >
> How you would implement it? Introducing the procedure identifier in
> the local scope with the possibility of shadowing it by another local
> declaration? Of course in a clean way :-)
We can maintain a stack of procedure identifiers which reflects the 
current procedure nesting. On a procedure call we look for the procedure 
identifier

1. in the current scope
2. on the top of the stack
3. in the global scope.

Then a procedure like this will behave as expected:

    PROCEDURE Sum(a: ARRAY OF INTEGER; n: INTEGER): INTEGER;

       PROCEDURE Sum(a: ARRAY OF INTEGER; n, s: INTEGER): INTEGER;
          VAR result: INTEGER;
       BEGIN
          IF n > 0 THEN
             result := Sum(a, n - 1, s + a[n - 1])
          ELSE
             result := s
          END
       RETURN result
       END Sum;

    RETURN Sum(a, n, 0)
    END Sum

However, it may be more clear to use a distinct name for the local 
procedure.


August