I have implemented a small example in two versions: one with external dllist (I'm using the Batteries Dllist module), which indeed needs a small hack to bootstrap a single-element cycle, and one with inline pointers as you show, using simple value recursion. In the second case I also have a small abstraction layer for traversals -- only instantiated in the 'iter' case currently -- that could save some code duplication; that must be one of the "closures" tricks you were thinking of, but I don't claim that it's as efficient than duplicated specialized traversal functions.
The code is here: https://gitorious.org/gasche-snippets/outside-or-inline-lists/blobs/master/goswin_dllists.ml On Thu, Mar 8, 2012 at 6:11 AM, Goswin von Brederlow <goswin-...@web.de> wrote: > Gabriel Scherer <gabriel.sche...@gmail.com> writes: > >>> So then you need mutable option types or mutables that you initialize >>> with dummy values and then overwrite with the real thing once all >>> members of a cycle are created. Or some other trickery to make it >>> work. Overall cycles are generally not good. >> >> I believe the trick you need (either passing a dummy value of your >> type, or Obj.magic) is less ugly that your Camlp4 solution for inline >> access. >> If I really needed absolute performance, I'd use the inline version >> just like in C, with mutable fields, but without preprocessor sugar. >> Preprocessing could avoid a bit of duplication (corresponding to >> manual inlining) on the structure-definition side, but wouldn't >> simplify the structure-using code much. > > How? > > type task = { > mutable all_next : task; > mutable all_prev : task; > mutable state_next : task; > mutable state_prev : tast; > ... > } > > Now how do yout write DList.insert, DList.remove, DList.iter, ...? > > I'm looking for some nice tricks using closures, functors, first class > modules or something to make it look pretty and easy to use. > > I do have an ugly solution but I'm hoping for some fresh idea not based > on what I already know is ugly. I can't be the only one that found the > need to keep an item in two containers and be able to remove it from > both quickly, right? > > MfG > Goswin -- Caml-list mailing list. Subscription management and archives: https://sympa-roc.inria.fr/wws/info/caml-list Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
