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Hi everyone,

I have created an implementation of N4244 resumable lambdas as a C++ to C++
preprocessor. You can find out more about it on GitHub here:

http://chriskohlhoff.github.io/resumable-pp/

Please note that there are some differences from N4244 due to the
limitations of not being part of a real compiler. These are documented at
the above site. There is also a link to the examples and an online form to
run the preprocessor for those who don't want to build it from source.

Here's one simple example (countdown4.cpp):

#include <stdio.h>

auto countdown(int n)
{
  return [=]() resumable
  {
    while (--n > 0)
      if (n == 1) return n;
      else yield n;
  };
}

int main()
{
  auto f = [&]() resumable
  {
    yield from countdown(10);
    return from countdown(5);
  };

  while (!is_terminal(f))
    printf("%d\n", f());
}

Though I haven't put in much effort to optimise the implementation,
performance is good because the compiler is able to see right into the
lambda implementation. Running this:

auto f = countdown(1000000000);
while (!f.is_terminal())
  f();

takes just 0.4 seconds to complete, or 0.4ns per iteration, as the compiler
has optimised everything away bar the test, increment and jump.

Cheers,
Chris

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<div dir=3D"ltr">Hi everyone,<div><br></div><div>I have created an implemen=
tation of N4244 resumable lambdas as a C++ to C++ preprocessor. You can fin=
d out more about it on GitHub here:</div><div><br></div><div><a href=3D"htt=
p://chriskohlhoff.github.io/resumable-pp/">http://chriskohlhoff.github.io/r=
esumable-pp/</a><br></div><div><br></div><div>Please note that there are so=
me differences from N4244 due to the limitations of not being part of a rea=
l compiler. These are documented at the above site. There is also a link to=
 the examples and an online form to run the preprocessor for those who don'=
t want to build it from source.</div><br>Here's one simple example (countdo=
wn4.cpp):<br><br>#include &lt;stdio.h&gt;<br><br>auto countdown(int n)<br>{=
<br>&nbsp; return [=3D]() resumable<br>&nbsp; {<br>&nbsp; &nbsp; while (--n=
 &gt; 0)<br>&nbsp; &nbsp; &nbsp; if (n =3D=3D 1) return n;<br>&nbsp; &nbsp;=
 &nbsp; else yield n;<br>&nbsp; };  <br>} <br>  <br>int main()<br>{   <br>&=
nbsp; auto f =3D [&amp;]() resumable<br>&nbsp; {   <br>&nbsp; &nbsp; yield =
from countdown(10);<br>&nbsp; &nbsp; return from countdown(5);<br>&nbsp; };=
<br>    <br>&nbsp; while (!is_terminal(f))<br>&nbsp; &nbsp; printf("%d\n", =
f());<br>} <br><br>Though I haven't put in much effort to optimise the impl=
ementation, performance is good because the compiler is able to see right i=
nto the lambda implementation. Running this:<br><br>auto f =3D countdown(10=
00000000);<br>while (!f.is_terminal())<br>&nbsp; f();<br><br>takes just 0.4=
 seconds to complete, or 0.4ns per iteration, as the compiler has optimised=
 everything away bar the test, increment and jump.<div><div><br></div><div>=
Cheers,</div><div>Chris</div></div></div>

<p></p>

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