Representing the cost of control

Every once in a while I play around with this idea for the design of a web language (server-side).

The nice thing about using first-class continuations to implement a web library is that you can write your code in direct style, but a big down-side is that you still have to figure out how to manage the storage of those continuations. But the alternative of essentially representing the control with program data structures, i.e. with explicit representations of the state of the computation, is really painful.

So I've thought of taking a page from Haskell's playbook: what if you separated a web language into two portions? One language would be for writing the "driver" of the program, where you can call send/suspend and computations may be suspended and restarted an arbitrary number of times. The other language would be "pure" (well, let's say full Scheme, but no send/suspend). In other words, replace Haskell's IO monad with the Web monad. As with Haskell, code in the Web monad can call pure code, but not vice versa.

The benefit of this would be that you could still write in direct style, but you've made explicit the portions of the program where control will cost you. Then you could play with different ways of managing that cost--expiration of continuations, back-off for expiration, etc.--by playing with the design of the Web monad, which wouldn't affect the pure language.