On 2015-05-21 at 14:09:13 +0200, Yitzchak Gale wrote:
I wrote:
...I thought that the idea was that we wanted it actually integrated into GHC.
Herbert Valerio Riedel wrote:
That would be the preferred way from a technical standpoint, as it would avoid fork/exec and make it easier to integrate the CPP-phase tighter into the lexer/parser.
However, due to the, sadly, mostly non-technical issues brought up, it seems to me that isolating cpphs into a separate process (w/ the option to configure GHC to use some other cpp implementation at your own risk if you need to avoid the cpphs implementation at all costs) would be the compromise acceptable to everyone in the short run while addressing the primary goal to decouple the default-configuration of GHC from the fragile system-cpp semantics.
Correct me if I'm wrong:
GHC already supports using an external CPP processor as an option. And cpphs is already easily buildable as a stand-alone external CPP processor compatible with GHC.
Yes
So can't we incorporate cpphs into GHC as is, but also provide a build option to exclude it from a GHC build? In a non-cpphs build, CPP would only work if an external processor is provided.
Well, that's more or less the plan (I hinted at in what I wrote earlier) for cpphs-as-an-executable/isolated-process; Except that we may[1] not want to build a cpphs as you'd get if you simply 'cabal install cpphs' (as that would pull in more build-deps than desirable), but maybe implement a stripped down GHC-specific frontend to the cpphs library (while trying keep the original cpphs modules untouched, and/or contributing changes back to upstream so we don't diverge). In any case, the cpphs-ish tool bundled with GHC could be considered a GHC-specific fork of cpphs (and possibly with a GHC-tailored CLI) *and* you'd have the option as you suggest to exclude it from the GHC build, in order to create a GHC toolchain w/o any "cpphs" code (which uses e.g. the system-cpp as in the past).
That's even better than the GMP situation - it really would be simple and practical to create and use a non-cpphs GHC if needed. As opposed to a non-GMP build, which in reality is only a theoretical possibility to satisfy the lawyers.
[1]: I'm just thinking out loud here; it'll only become clear what's sensible once we have *actually* attempted to integrate cpphs into the GHC build-system, and have a working proof of concept (that'll need to be thrown at Hackage)