On Mon, Oct 10, 2011 at 1:33 PM, Dean Landolt <[email protected]> wrote:
> > > On Wed, Oct 5, 2011 at 1:40 PM, Bob Nystrom <[email protected]> wrote: > >> >> >> 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? >> > > > Woah there -- where does this syntax come from? Was `walk(tree) {...}` > supposed to be `function* walk(tree) {...}` instead? Or is this intended to > represent some sort of method generator? If the latter, doesn't this need > some mechanism to distinguish it from a non-generator method? > Whoops, my mistake. Too much time working on the class proposal where "function" isn't needed for methods. Yes, that should be function*. - bob
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