--- each([rs]) {|line| ... }
--- each_line([rs]) {|line| ... }

    IO ݡȤ 1 Ԥɤ߹Ƿ֤ƥ졼IO ݡȤϥ꡼
    ɥ⡼ɤǥץ󤵤Ƥɬפޤ(open
    )

    Ԥζڤϰ rs ǻꤷʸˤʤޤrs 
    ǥեͤϥƥѿ $/ ͤǤ

    rs  nil ꤹȹԶڤʤȤߤʤޤ
    ʸ "" ꤹϢ³ԤԤζڤȤߤʤޤ
    (ѥ饰ե⡼)

    self ֤ޤ

