On Mon, Oct 27, 2014 at 01:08:24PM -0500, Matthias Felleisen wrote: > > In my 30 year career as a Schemer and Racketeer, I have found > one successful use for (upward) continuations in the world of > search, to be precise so-called "intelligent search". That's a > 1970s concept from AI. You have a complex search space and a decision > functions on which subspaces to search next given certain conditions > on the current state of the search. At each decision point, you compute > the next best choice, which includes all backtracking points. All > subspaces that aren't searched are marked as such backtracking points, > which is information about the space plus a continuation, which knows > how to resume the search in this world. Then you enter the next subsapce, > which is equivalent to throwing a continuation.
Yes, that's the kind of thing had in mind. Are there any examples or other information available about it, or is it time to start reinventing t from scratch. Maybe Steele had something? He did invent Scheme in the context of a lab that was trying to invent AI languages, which at that tie seemed to mean intelligent search. > > I know that there are many papers that use continuations for searches. > For most of these examples and most implementations, the algorithm is > neither as performant as one that passes continuations via closures > nor any easier to understand than one that explicitly manipulates > success and fail continuations. > > My judgement for the second point is different when this kind of code > is what a macro expands into and continuations are highly performant. Macro expansion, or something like it, is probably the way I'd do it. > > ---------------------------------------------------------------- > > Having said that, I do wish to emphasize that continuations are > useful in other contexts and every time I am about ready to throw > them out of a language, I find one more reason not to do so. Plus, > if you accept that the language should handle arbitrarily deep > recursion, you have all the implementation concepts worked out > anyway (mostly) so adding continuations to the language costs very > little. They are what makes Scheme different from other languages. They're the reason that I am picking Scheme (likely typed Scheme initially) instead of OCaml for ths project. So please don't get rid of them -- hendrik ____________________ Racket Users list: http://lists.racket-lang.org/users
