ertes 2017-02-08 19:59:11
ezyang: because it's just a dummy type
ertes 2017-02-08 19:59:36
ezyang: in particular it (e.g. Spider) is not the host monad (e.g. SpiderHost)
ertes 2017-02-08 20:00:08
all it does is to represent an abstract notion of "timeline"
