digitalmars.D - yield iteration
- "anonymous" <anonymous example.com> Jul 29 2012
- "bearophile" <bearophileHUGS lycos.com> Jul 29 2012
- "Tobias Pankrath" <tobias pankrath.net> Jul 29 2012
- Timon Gehr <timon.gehr gmx.ch> Jul 29 2012
- Timon Gehr <timon.gehr gmx.ch> Jul 29 2012
- "bearophile" <bearophileHUGS lycos.com> Jul 29 2012
A subthread of the "Impressed" thread revolved around D's lack of
a yield mechanism for iteration.
Nick Sabalausky mentioned his earlier attempt to create a library
based yield which unfortunately was too slow to compete with
explicit opApply/ranges [1].
I took a shot at it. It's fast. The resulting code is reasonably
pretty. But it doesn't provide a range interface, just opApply.
---
module yielder;
import core.thread;
/**
Examples:
---
import yielder;
import std.stdio;
auto y = new class Yielder!int {
final void yielding() {
yield(0);
yield(13);
yield(42);
}
};
foreach(x; y) {
writeln(x);
}
---
*/
class Yielder(E) {
abstract void yielding();
this() {
this.fiber = new Fiber(&yielding);
}
private {
Fiber fiber;
int result;
int delegate(ref E) callback;
}
final int opApply(int delegate(ref E) cb) {
callback = cb;
result = 0;
fiber.reset();
fiber.call();
return result;
}
final void yield(ref E value) {
result = callback(value);
if(result != 0) {
Fiber.yield();
}
}
final void yield(E value) {
yield(value);
}
}
---
[1]
https://semitwist.com/articles/article/view/combine-coroutines-and-input-ranges-for-dead-simple-d-iteration
Jul 29 2012
anonymous:A subthread of the "Impressed" thread revolved around D's lack of a yield mechanism for iteration.
The yield as in Python is so useful and handy, and I miss it often in D. This is an example of Inverse Gray iterator (Sloane series A006068) Python2 code from: http://code.activestate.com/recipes/221457/ def A006068(): yield 0 for x in A006068(): if x & 1: yield 2 * x + 1 yield 2 * x else: if x: yield 2 * x yield 2 * x + 1 Turning that in D code that uses opApply is not hard, but the code inflates 3X, and you can't use most std.algorithm on it. I have discussed the situation a little here: http://d.puremagic.com/issues/show_bug.cgi?id=5660 Bye, bearophile
Jul 29 2012
"bearophile" , dans le message (digitalmars.D:173647), a écrit :Turning that in D code that uses opApply is not hard, but the code inflates 3X, and you can't use most std.algorithm on it.
I believe most std.algorithm that work on input range could be made to work with opApply, or opApply-like delegates. It just wouldn't be particularly efficient unless agressive inlining is used. For example, filter could work like this for opApply-like delegates: template filter(pred) { auto filter(T)(int delegate(int delegate(ref T)) apply) { return (int delegate(ref T) dg) { return apply( (ref T t) { return pred(t)? dg(t): 1; }); } } } -- Christophe
Jul 31 2012
travert phare.normalesup.org (Christophe Travert) Christophe Travert, dans le message (digitalmars.D:173787), a écrit :"bearophile" , dans le message (digitalmars.D:173647), a écrit :Turning that in D code that uses opApply is not hard, but the code inflates 3X, and you can't use most std.algorithm on it.
I believe most std.algorithm that work on input range could be made to work with opApply, or opApply-like delegates. It just wouldn't be particularly efficient unless agressive inlining is used. For example, filter could work like this for opApply-like delegates: template filter(pred) { auto filter(T)(int delegate(int delegate(ref T)) apply) { return (int delegate(ref T) dg) { return apply( (ref T t) { return pred(t)? dg(t): 1; });
} } } -- Christophe
Jul 31 2012
This is an example of Inverse Gray iterator (Sloane series A006068) Python2 code from: http://code.activestate.com/recipes/221457/ def A006068(): yield 0 for x in A006068(): if x & 1: yield 2 * x + 1 yield 2 * x else: if x: yield 2 * x yield 2 * x + 1
Does this spawn linear many generators?
Jul 29 2012
Ideally it would look like this:
struct Map(alias fun, R){
R range;
mixin YieldInputRange!q{
for(; !range.empty; range.popFront())
yield fun(range.front);
}
static if(is(typeof(range.save))) property auto save(){
return Map!(fun, R)(range.save);
}
...
}
Or as a built-in:
struct Map(alias fun, R){
R range;
yield {
for(; !range.empty; range.popFront())
yield fun(x);
}
static if(is(typeof(range.save))) property auto save(){
return Map!(fun, R)(range.save);
}
...
}
Jul 29 2012
On 07/29/2012 04:48 PM, Timon Gehr wrote:Ideally it would look like this: struct Map(alias fun, R){ R range; mixin YieldInputRange!q{ for(; !range.empty; range.popFront()) yield fun(range.front); } static if(is(typeof(range.save))) property auto save(){ return Map!(fun, R)(range.save); } ... } Or as a built-in: struct Map(alias fun, R){ R range; yield { for(; !range.empty; range.popFront()) yield fun(x);
} static if(is(typeof(range.save))) property auto save(){ return Map!(fun, R)(range.save); } ... }
Jul 29 2012
Tobias Pankrath:Does this spawn linear many generators?
I have written this little test code, Python2.6+: count = 0 def A006068(): global count count += 1 yield 0 for x in A006068(): if x & 1: yield 2 * x + 1 yield 2 * x else: if x: yield 2 * x yield 2 * x + 1 from itertools import islice def main(): global count for p in xrange(15): n = 2 ** p count = 0 print sum(1 for _ in islice(A006068(), 0, n)), count main() The output seems to show that it spawns only logarithmically: 1 1 2 2 4 3 8 4 16 5 32 6 64 7 128 8 256 9 512 10 1024 11 2048 12 4096 13 8192 14 16384 15 Bye, bearophile
Jul 29 2012