Re: [boost] Yap's formal review is starting now!

On Mon, Feb 5, 2018 at 9:53 AM, Louis Dionne via Boost < boost@lists.boost.org> wrote:

Dear Boost community,

The formal review of Zach Laine's Yap library starts Monday, February 5th and ends on Wednesday, February 14th.

<snip>

We encourage your participation in this review. At a minimum, please state:

- Whether you believe the library should be accepted into Boost

I recommend Boost ACCEPT Yap as a new library.

- Your name

Barrett Adair

- Your knowledge of the problem domain

At best, average for this mailing list -- probably less. I am familiar and comfortable with hand-rolled expression templates, but I have not (successfully) used Proto.

You are strongly encouraged to also provide additional information:

- What is your evaluation of the library's: * Design

I agree that Boost needs a modern replacement for Proto, and Yap appears to do this with flying colors (as far as my untrained eye can tell).

* Implementation

Did not review. My only comment on the implementation is a minor usability note - a recurring point of frustration for me was that gcc 7.2 errors print expr_kind template value parameters as integer values instead using enum member names, e.g. `meow_expr<(boost::yap::expr_kind)18, boost::hana::tuple<meow>>`. This adds a layer of mental indirection when debugging an expression tree. A very small nice-to-have, if nothing else, would be to assign explicit enum values in boost/yap/algorithm_fwd.hpp for faster cross-referencing.

* Documentation

...can never be good enough, but I'm happy with this. It's pleasantly concise, and it seems complete. I'm confident that I could become proficient with Yap given what is available here. I do think the docs would benefit from the following: * less nesting of sections * a link to Zach's C++Now talk (if the talk still reflects the code, that is) * more examples, as always * Some sections could be merged, such as "operators" and "operator macros", also the transform sections * The "operator macros" section would benefit from having the expr_kind names listed nearby This documentation appears to cater to Proto alumni, which is fine, but an "Intro to Expression Templates" section would be nice for newcomers. A "Suggested reading" section would also be a cheap way to improve accessibility. Smoothing out the cliff-shaped learning curve of this library is a daunting task, but it might be worthwhile in the long run.

* Tests

Built, ran, passed, did not review. Ubuntu 16, gcc 7.2, Boost 1.66

* Usefulness

I have not written an EDSL complex enough to need Proto or Yap, but I can see why this library would be useful.

- Did you attempt to use the library? If so: * Which compiler(s)?

gcc 7.2

* What was the experience? Any problems?

I played around with transforming variations of the following: template struct letter_expr { static boost::yap::expr_kind const kind = Kind; Tuple elements; BOOST_YAP_USER_BINARY_OPERATOR_MEMBER(minus, ::letter_expr) }; #define DEFINE_LETTER(c) auto c = boost::yap::make_terminal(std::string{#c}) DEFINE_LETTER(A); DEFINE_LETTER(B); DEFINE_LETTER(C); DEFINE_LETTER(D); // ... auto foo = H-E-L-L-O-W-O-R-L-D; I'd hoped to get further than I did. I tried and failed to implement a cloud-to-butt [0] transform in the time that I had. I was able to see the library in action and implement some very simple transforms. The documentation and examples were helping me through my issues.

- How much effort did you put into your evaluation of the review?

1 hour reading examples and documentation, 2 hours hacking around, 1 hour writing this review, 0 hours catching up on previous reviews of Yap. Thanks, Barrett [0] https://github.com/panicsteve/cloud-to-butt