RFC: "Native -XCPP" Proposal

Andrés Sicard-Ramírez asr at eafit.edu.co
Wed May 6 13:43:03 UTC 2015

I want to emphasize that cpphs is actively maintained as it's pointed
out in https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCp. The
Agda team has found some cpphs bugs which have been *quickly* fixed by
cpphs's author, Malcolm Wallace. Unfortunately I have not been able to
track down the problem mentioned by Janek Stolarek.

On 6 May 2015 at 06:38, Jan Stolarek <jan.stolarek at p.lodz.pl> wrote:
> One thing to keep in mind is that while cpphs will solve some problems of system-cpp, it will also
> bring problems of its own. I, for one, have run into problems with it when installing Agda. There
> is a very long thread here:
> https://lists.chalmers.se/pipermail/agda/2014/006975.html
> and twice as more on my private inbox. We've reached no conclusion about the cause and the only
> solution was to use system-cpp.
> Regarding licensing issues: perhaps we should simply ask Malcolm Wallace if he would consider
> changing the license for the sake of GHC? Or perhaps he could grant a custom-tailored license to
> the GHC project? After all, the project page [1] says: " If that's a problem for you, contact me
> to make other arrangements."
> Janek
> [1] http://projects.haskell.org/cpphs/
> Dnia środa, 6 maja 2015, Herbert Valerio Riedel napisał:
>> Hello *,
>> As you may be aware, GHC's `{-# LANGUAGE CPP #-}` language extension
>> currently relies on the system's C-compiler bundled `cpp` program to
>> provide a "traditional mode" c-preprocessor.
>> This has caused several problems in the past, since parsing Haskell code
>> with a preprocessor mode designed for use with C's tokenizer has caused
>> already quite some problems[1] in the past. I'd like to see GHC 7.12
>> adopt an implemntation of `-XCPP` that does not rely on the shaky
>> system-`cpp` foundation. To this end I've created a wiki page
>>   https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCpp
>> to describe the actual problems in more detail, and a couple of possible
>> ways forward. Ideally, we'd simply integrate `cpphs` into GHC
>> (i.e. "plan 2"). However, due to `cpp`s non-BSD3 license this should be
>> discussed and debated since affects the overall-license of the GHC
>> code-base, which may or may not be a problem to GHC's user-base (and
>> that's what I hope this discussion will help to find out).
>> So please go ahead and read the Wiki page... and then speak your mind!
>> Thanks,
>>   HVR
>> [1]: ...does anybody remember the issues Haskell packages (& GHC)
>>      encountered when Apple switched to the Clang tool-chain, thereby
>>      causing code using `-XCPP` to suddenly break due to subtly
>>      different `cpp`-semantics?
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