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Subject: Re: [boost] [preprocessing] Feedback requested on a C99 preprocessor written in pure universal Python
From: Edward Diener (eldiener_at_[hidden])
Date: 2017-03-06 22:51:12

On 3/6/2017 3:46 PM, Niall Douglas via Boost wrote:
> On 06/03/2017 19:10, Edward Diener via Boost wrote:
>> On 3/6/2017 5:45 AM, Niall Douglas via Boost wrote:
>>> Those of you who watch reddit/r/cpp will know I've been working for the
>>> past month on a pure Python implementation of a C99 conforming
>>> preprocessor. I am pleased to be able to ask for Boost feedback on a
>>> fairly high quality implementation:
>> It would be nice, for the purpose of testing with Boost PP and Boost
>> VMD, if somehow your preprocessor could somehow be plugged in to one of
>> the compilers Boost supports, with VC++ being the most obvious choice
>> because its preprocessor is not C++ standard conforming.
> It's pretty straightforward in theory. pcpp can consume from stdin or a
> file, and can output to stdout or a file, so it's easy to insert into a
> sequence using the pipe operator (which works fine on Windows too).
> An alternative is to simply feed its output to any compiler, pcpp marks
> up the output with # lineno filepath exactly the same as a normal
> preprocessor so the compiler can track the original source files. Those
> should be passed through by any preprocessor unchanged, including MSVC's.

How do I identify pcpp as the preprocessor in Boost PP or Boost VMD code
? In other words does pcpp predefine some macro(s) that identifies
itself and/or its level of C/C++ preprocessor conformance ? If it does I
can check for this in the Boost PP configuration and set the level of
C++ standards conformance and variadic macro support in the Boost PP
configuration file. This would better enable Boost PP/Boost VMD to work
with pcpp.

>> There may be
>> some other way of directly creating a toolset with your preprocessor in
>> order to test it in Boost, but I am not knowledgeable enough with Boost
>> Build to know how to do this. If you, or somebody else, could do this it
>> would surely be welcome by me and probably by yourself.
> I would be no more skilled than you at persuading Boost.Build to do
> this. Even in cmake, it's tricky to inject a custom command inheriting
> the current compiler flags i.e. all the -D's, -I's etc.
>>> (and yes it is also a Python library as well as a command line tool, you
>>> can find API reference docs at
> Another big use case could be for debugging complex preprocessing
> because it's very easy to hook in and introspect preprocessing as it is
> being executed. But as I've mentioned, I've not tested it with really
> complex preprocessor metaprogramming, getting it this far has already
> taken me a month and I suspect my unemployment will be ending soon, so
> my free time will return to nil. Still, it was a nice diversion away
> from C++ and it has refreshed my Python skills very nicely.
> Niall

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