Unconditional:

      FOR num-unsubs-var = num-exp1 TO num-exp2 [ STEP num-exp3 ]

          [ statement ]...

      NEXT num-unsubs-var

  Conditional:

                                                    {UNTIL}
      FOR num-unsubs-var = num-exp1 [STEP num-exp3] {WHILE} cond-exp

          [ statement ]...

      NEXT num-unsubs-var

  Unconditional Statement Modifier:

      statement FOR num-unsubs-var = num-exp1 TO num-exp2 [STEP num-exp3]

  Conditional Statement Modifier:

      statement FOR num-unsubs-var = num-exp1 [step num-
             exp3] {WHILE} cond-exp