Re: [boost] [preprocessing] Feedback requested on a C99 preprocessor written in pure universal Python

On 3/6/2017 6:56 PM, Andrey Semashev via Boost wrote:

On Mon, Mar 6, 2017 at 11:46 PM, Niall Douglas via Boost wrote:

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On 06/03/2017 19:10, Edward Diener via Boost wrote:

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On 3/6/2017 5:45 AM, Niall Douglas via Boost wrote:

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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:

https://github.com/ned14/pcpp

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).

Given that preprocessor checks are often used for compiler workarounds, and pcpp is not a full C++ frontend, one would have to make sure pcpp defines the same set of predefined macros the compiler does. In the particular case of MSVC that would make libraries like Boost.PP and Boost.VMD treat pcpp the same way they do MSVC, which is probably suboptimal, if at all functional. I guess, for such tandem to be workable, pcpp has to define its own predefined macros, and PP and VMD have to test it before they test other compiler-specific macros.

Exactly ! Still merely to run the Boost PP and Boost VMD tests, which are decent tests for much hardcore C++ standard preprocessor conformance, pcpp could minimally define __cplusplus >= 201103L or __STDC_VERSION__ >= 199901L, without necessarily identifying itself otherwise, and Boost PP/Boost VMD will treat the preprocessor as strictly C++ standard conformant with variadic macro support. But what you write above is certainly correct in general, in order to test other Boost libraries and end-user's code, with pcpp as the preprocessor for some other compiler. BTW Boost already has an almost complete conformant C++ preprocesor in Boost Wave. I could not have developed VMD or helped support Boost PP without its ability to show correct macro expansion. It has been absolutely invaluable in that respect.