--- step(limit, step) {|n| ... }

    self Ϥ step ­ʤ limit ۤ
    ޤǥ֥å򷫤֤ޤstep οǤޤ
    ޤlimit  step ˤ Float ʤɤǤޤ

    step  0 ꤷ㳰 ArgumentError ȯޤ

    self ֤ޤ

    upto, downto, times ⻲ȡ

    step ⻲ȡ

