On Wed, Oct 5, 2011 at 7:18 AM, John J Barton <[email protected]>wrote:
> > > On Tue, Oct 4, 2011 at 2:33 PM, Bob Nystrom <[email protected]> wrote: > >> That's correct. That's often the cost of concision. By analogy: you can do >> a lot of stuff using either an explicit stack data structure or recursion. >> Using recursion is often more concise but then the state is hidden from you >> in the callstack. Sometimes that's a good trade-off, sometimes it's not. > > > Thanks, that analogy helps confirm my opinion of generators. In my > experience, the good trade-off is recursion on data structures and the > not-good-trade-off is recursion for iteration. > Yes, I wasn't making any claim about using recursion *for iteration*. Maybe I need to be more concrete here: If you need to walk a tree, you can do so using recursion or you can use an explicit stack data structure. The former is usually more terse (because it implicitly relies on the callstack itself storing the stack) but the other can be more clear. *By analogy*, if you need to produce a sequence of values, you can do so using generators, or you can use an explicit iterator object. Again, the former is usually more terse (because the language automatically creates the iterator object for you given a function containing yield) but the latter can be more clear (because the state is laid bare). Note that those two paragraphs are separate. I'm not talking about using recursion for iteration. Is this clearer now? So far the only examples I've seen for generators involve iteration. Yup, that's what generators do. And recursion involves stacks. I've heard no clamor at all. > That may be true, but it may say as much about your surrounding auditory environment as it does the feature in question. You may be right, but simply saying "Bigfoot isn't in my living room" doesn't disprove the existence of Bigfoot. There *are* languages in wide use that have this feature. None of those languages (Lua, C#, Python) has a reputation for catering to the esoteric programming language fanbase. Really this is a niche feature, an aid for the rare case where conventional > iterators are a poor match. > They said the same thing about closures. I agree that generators aren't the most important language feature in the world, but I think if you had them you'd find that you used them. Here's an example: let tree = [['a', 'b', 'c'], [['d', 'e'], 'f'], ['g']]; let inOrder = walk(tree); for (node of walk(tree)) alert(node); // a, b, c, d, ... walk(tree) { if (typeof tree == 'string') { yield tree; // leaf } else { yield* walk(tree); // branch } } What would the above look like without generators? - bob
_______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
