Listing:

    1  MODULE PFwd;
    2  VAR ExitCode : INTEGER;
    3  PROCEDURE Even(n : INTEGER) : BOOLEAN;
    4  FORWARD;
    5  PROCEDURE Odd(n : INTEGER) : BOOLEAN;
    6  BEGIN
    7    IF n = 0 THEN RETURN FALSE ELSE RETURN Even(n - 1) END
    8  END Odd;
    9  PROCEDURE Even(n : INTEGER) : BOOLEAN;
   10  BEGIN
   11    IF n = 0 THEN RETURN TRUE ELSE RETURN Odd(n - 1) END
   12  END Even;
   13  BEGIN
   14    IF Even(10) THEN ExitCode := 1 ELSE ExitCode := 0 END
   15  END PFwd.

    0 errors