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. Yes. It was not my intention to imply in any way that cpphs suffers from maintanance issues.

Unfortunately I have not been able to track down the problem mentioned by Janek Stolarek. Yes, and that's what gets me worried. I suppose the problem was somehow related to my locale settings although we were unable to track down the cause. I also recall someone else reported being affected by the same problem. So, until that problem is solved I would say it is a blocker as it would essentialy make development of GHC impossible for some people.

Janek

On 6 May 2015 at 06:38, Jan Stolarek 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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On 2015-05-06 at 13:38:16 +0200, Jan Stolarek wrote: [...]

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."

Fyi, Neil talked to him[1]: | I talked to Malcolm. His contention is that it doesn't actually change | the license of the ghc package. As such, it's just a single extra | license to add to a directory full of licenses, which is no big deal. [1]: http://www.reddit.com/r/haskell/comments/351pur/rfc_native_xcpp_for_ghc_prop...

Perhaps it makes sense to scan hackage to find all the different CPP idioms that are actually used in Haskell code, if it is a small/well-defined set it may be worth writing a simple custom preprocessor. Alan On Wed, May 6, 2015 at 3:03 PM, Mikhail Glushenkov < the.dead.shall.rise@gmail.com> wrote:

On 6 May 2015 at 14:25, Austin Seipp wrote:

...

2) The lexing rules for C and Haskell simply are not the same in general.

One area where this is irritating is that it makes it impossible to use Haskell multiline strings together with CPP. _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

At the risk of antagonizing some (most? all?) of you, how about... -XCPP stands for the native CPP -XGNUCPP stands for GNU's GCC CPP -XClangCPP stands for Clang's CPP -XCPPHS stands for CPPHS ... with the hope that TH is the future? Howard

Howard B. Golden wrote:

At the risk of antagonizing some (most? all?) of you, how about...

-XCPP stands for the native CPP -XGNUCPP stands for GNU's GCC CPP -XClangCPP stands for Clang's CPP -XCPPHS stands for CPPHS

Oh please no! If someone releases a package on Hackage that uses -XGNUCPP, that will likely break on OSX because on OSX, gcc is actually clang.

... with the hope that TH is the future?

I suspect there will always be things that CPP does better than TH. What we need is a better CPP. Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

On Wed, May 6, 2015 at 11:36 AM, Stephen Paul Weber < singpolyma@singpolyma.net> wrote:

Yes. This is one of my favourite things in GHC-land -- that an existing, good-enough, standardised, and widely-deployed solution was chosen over a NiH reinvention of preprocessing

I have to assume my irony detector is broken as well. Or maybe I should just assume that "all the world's Linux with gcc" is assumed to be forever true and forever reliable by "all right-thinking people" so let's just sweep the nonissue under the rug because it can oh so obviously never be a real issue.... Because I had to face this back a couple decades ago, when my employer ported an application written in a 4GL (database language) to SCO Unix. The 4GL assumed cpp was the ever reliable pcc one and broke very badly when SCO used one integrated into its lexer (making it even more tightly wedded to C syntax than clang's). Eventually we replaced its cpp with a wrapper that ran m4 and redid everything else in m4's syntax. Which is why I was always a bit worried about ghc relying on cpp, was unsurprised when clang caused issues, and am rather annoyed that there are people who believe that they can just ignore it because REAL users will always be on Linux with gcc and all them furriners using weird OSes like OS X and FreeBSD can safely be ignored with their not-the-One-True-OS-and-compiler platforms. Additional historical note that I assume True Believers will ignore as meaningless: X11 used to make the same assumption that cpp was always and forever guaranteed to be friendly to non-C and this still shows at times in things like xrdb resource databases. They did accept the inevitable and (mostly) stop abusing it that way, and are now moving away from imake which likewise assumes it's safe to use cpp on Makefiles. (And yes, I encounter the same inability to comprehend or accept change there.) -- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net

I have no problem with plan 4. However, I'll point out that implementing CPP is not *that* hard... :) Cheers, Simon On 18/06/2015 09:32, Herbert Valerio Riedel wrote:

Hello *,

Following up on the "Native -XCPP" Proposal discussion, it appears that cpphs' current LGPL+SLE licensing doesn't pose an *objective* showstopper problem but is rather more of an inconvenience as it causes argumentation/discussion overhead (which then /may/ actually result in Haskell being turned down eventually over alternatives that do without LGPL components).

In order to acknowledge this discomfort, for GHC 7.12 we propose to follow "plan 4" according to [1] (i.e. calling out to a cpphs-executable as a separate process), thereby avoiding pulling any LGPL-subjected cpphs code into produced executables when linking against the 'ghc' package.

"Plan 2" (i.e. embedding/linking cpphs' code directly into ghc) would reduce fork/exec overhead, which can be substantial on Windows [2], but plan 4 is no worse than what we have now.

Last Call: Are there any objections with GHC adopting "plan 4"[1]?

[1]: https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCpp

[2]: http://permalink.gmane.org/gmane.comp.lang.haskell.ghc.devel/8869

Thanks, HVR

On 2015-05-06 at 13:08:03 +0200, Herbert Valerio Riedel wrote:

...

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?