3 ms·

> it requires the list of return values to be precomputed. I thought Scheme's semantics were allowed to be lazy to some extent, but I'm unaware of the finer po

by lmkg 16y ago

> it requires the list of return values to be precomputed. I thought Scheme's semantics were allowed to be lazy to some extent, but I'm unaware of the finer points of it. Would a conforming implementation allow being lazy in this instance? I definitely agree that this seems like a strange place to pull out continuations. I get the impression that the author started from wanting an example of continuations, rather than an implementation of yield. As other people have pointed out, continuations and closures are equivalently powerful given CPS, but continuations seem simply gratuitous for this example. Just to make my point, here's my Common Lisp implementation: (defun generator (list last-val) (lambda () (if list (pop list) last-val))) Scheme would have to roll its own Pop macro, but I don't see how that would require a raw continuation primitive.

PieSquared 16y ago
I'm the one who wrote the post, and in retrospect I can see why people would be a bit confused at this example. I started out wanting to explain my actual implementation of a 'yield' command. As I wrote the post, though, it grew overcomplicated and filled with explanations of Scheme's syntax macros, which was not at all my intention. I guess in simplifying the implementation I also lost a bit of the idea behind it. You do need continuations to implement a general-case yield; if you just want generators for a list, you can use closers (and be more efficient, too). Thanks to you (and to parent) for pointing that out; if you don't mind, I'll add mention of what you said to the blog post?
- lmkg 16y ago
  By all means, go ahead =). I'm actually a fan of continuations, I just didn't see what the purpose was in the example that you gave. What would be helpful is an explanation of why a yield with continuations is more powerful than one with closures. That will probably require an explanation of what you mean by a "general-case yield" (I'm not that familiar with Python).

by lmkg 16y ago

PieSquared 16y ago

I'm the one who wrote the post, and in retrospect I can see why people would be a bit confused at this example. I started out wanting to explain my actual implementation of a 'yield' command. As I wrote the post, though, it grew overcomplicated and filled with explanations of Scheme's syntax macros, which was not at all my intention. I guess in simplifying the implementation I also lost a bit of the idea behind it. You do need continuations to implement a general-case yield; if you just want generators for a list, you can use closers (and be more efficient, too). Thanks to you (and to parent) for pointing that out; if you don't mind, I'll add mention of what you said to the blog post?

lmkg 16y ago
By all means, go ahead =). I'm actually a fan of continuations, I just didn't see what the purpose was in the example that you gave. What would be helpful is an explanation of why a yield with continuations is more powerful than one with closures. That will probably require an explanation of what you mean by a "general-case yield" (I'm not that familiar with Python).