Despite the subtle relationship with interpreter implementations, first-class continuations still have unique functionality. In this talk, I will describe how "callcc"---a control flow operator which is provided in library "continuation"---plays an important role in the context of domain specific language through the "do syntax" of list monads. In addition, I also claim how "callcc" has some inconveniences---cutting unnecessarily wide program pieces, and resulting in degraded executing performances---and introduce its advanced form, delimited continuation operators can resolve many issues.