PROGRAM invoke_funct
      EXTERNAL LONG FUNCTION FUN01(LONG, LONG, LONG)
      DECLARE LONG A, B, C
      INPUT "Please type three integers"; A, B, C
      PRINT "The sum is"; FUN01(A, B, C)
  END PROGRAM
  FUNCTION LONG FUN01 (LONG X, LONG Y, LONG Z)
      FUN01 = X + Y + Z
  END FUNCTION