Language Reference

Recursion

A procedure that can reference itself, directly or indirectly, is called a recursive procedure. Such a procedure can reference itself indefinitely until a specific condition is met. For example, you can determine the factorial of the positive integer N as follows:

INTEGER N, RESULT, FACTORIAL
READ (5,*) N
IF (N.GE.0) THEN
  RESULT = FACTORIAL(N)
END IF
CONTAINS
  RECURSIVE FUNCTION FACTORIAL (N) RESULT (RES)
    INTEGER RES
    IF (N.EQ.0) THEN
      RES = 1
    ELSE
      RES = N * FACTORIAL(N-1)
    END IF
  END FUNCTION FACTORIAL
END

For details on syntax and rules, see FUNCTION, SUBROUTINE, or ENTRY.

+-------------------------------IBM Extension--------------------------------+

You can also call external procedures recursively when you specify the -qrecur compiler option, although XL Fortran disregards this option if the procedure specifies either the RECURSIVE or RESULT keyword.

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