On 27/06/2009, at 10:18 AM, Erick Tryzelaar wrote: > I'm not sure if I completely understand you. As far as I can tell, > this is a technique to turn folds into cursors, which you could use to > write your polyadic functions.
I make two points: in C++, iterators + template hackery provides a weak (not type checked) form of polyadic programming. > For instance, we could take a cursor > and write: > > let count c = > let aux init c = > match Lazy.force c with > | None -> init > | Some i, c -> aux (init + i) c > in > aux 0 c > > And it should work with all cursors. Sure, but that's the point: cursors are polyadic if you can hide the container type in the function. > I interpreted it as as long as > you can create continuations, you can convert folds into cursors. And if you don't have them, you can do almost as well. > I don't think Oleg is saying that folds are always better, but that by > default ASTs should provide enumerators and convert them into cursors > when they're needed. He's saying enumerators are better because they provide certain guarantees that cursors don't. And I'm saying this is a false economy because managing the state variable in a fold to do the right thing is hard work, and re-introduces all the same problems anyhow. It is interesting there is a mechanical way to control invert to obtain cursors from enumerators, in a sufficiently powerful language. In Felix, fthreads do this (but only for procedures). First class continuations are a low level way to do "stack swapping". It's a pity Felix doesn't have first class functional continuations, but this is a consequence of using the C object model (i.e. Felix functions use the machine stack like C ones, allowing them to be freely mixed). -- john skaller skal...@users.sourceforge.net ------------------------------------------------------------------------------ _______________________________________________ Felix-language mailing list Felix-language@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/felix-language
