At Tue, 18 Sep 2012 19:20:29 +0200, Sam Tobin-Hochstadt wrote: > continuations are *not* used to > implement `thread` and associated facilities in Racket
Although Racket threads are not implemented with continuations in the sense of `continuation?', both threads and continuations use the same internal machinery for capturing context. As it happens, the run-time system knows some invariants for thread contexts so that it can swap them a little faster. Along those lines, it occurs to me that the implementation of `generator' might speed up by using `prompt' and `call/cc' instead of `shift' and `reset'. When I make that change, it cuts about 1/3 of the time from Greg and Patrick's examples. That's not a big improvement, but it helps explain the difference between threads and generators. Using `call/cc' for generators is effectively a hint to the run-time system that the continuation doesn't need to compose. That hint is useful only because of the way that continuations are implemented internally. ____________________ Racket Users list: http://lists.racket-lang.org/users
