[Haskell-cafe] Current status of Mavericks CPP

Brandon Allbery allbery.b at gmail.com
Wed Apr 16 06:16:41 UTC 2014

On Wed, Apr 16, 2014 at 2:05 AM, Michael Snoyman <michael at snoyman.com>wrote:

> I still seem to be getting bug reports about the CPP implementation of
> Mavericks. Last I'd heard, it seemed that general consensus was that
> packages should *not* be patched to work around the different CPP
> implementation, and instead Mavericks users should be installing GCC's CPP.
> Is this accurate? And is there a wiki page somewhere describing the
> situation and how to work around it? I'd like to have some authoritative
> URL to point people to, especially given that I have no access to a Mac
> system and therefore can't test this myself.

The correct answer is for ghc 7.8 to become established, because it removes
the dependency on an external C preprocessor. Some of the reasons for this

- with FreeBSD 10 having moved to clang on x86 / x86_64, it is clearly only
a matter of time before this becomes more than just a "Mavericks" issue;

- pretty much everyone *except* the Haskell community accepted that
expecting cpp to handle anything other than C and derivatives was a mistake
back when ANSI C came out;

- even with a K&R-style cpp like gcc -traditional, there are Haskell
constructs that can break it; consider that it must know how to parse
strings (there are some subtle differences between Haskell and C string
syntax) and char constants (did you know that C allows multi-character
(char) constants? and pretty much always has?) in order to know when to
expand macros. With an ANSI cpp like clang's, it must also know when to
interpret # and ## as splices.

brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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