[Haskell-cafe] RFC: "Native -XCPP" Proposal

[Nicola Gigante]

Il giorno 06/mag/2015, alle ore 23:07, Sven Panne <svenpanne at gmail.com> ha scritto:
> 
> More seriously: We don't want to break hundreds of packages on
> Hackage, the only thing we really need is a well-defined CPP-like
> preprocessor, so integrating e.g. cpphs somehow seems to be the right
> way IMHO. If it's not cpphs, I wouldn't mind, the main point is that
> it's the same on all platforms and handles basically *all* things CPP
> can.
> 

Hi all,

I'm following the discussion from the outside but I'm wondering if you have considered the following idea.

From what I understand the current problem with using the 
system's cpp is inconsistency between different compilers, is 
it?

Then why don't you _import_ the clang's preprocessor into 
GHC source tree and use that? As you probably know clang is 
not only a compiler, but a set of libraries to handle C/C++ 
code. AFAIK linking only the lexer module (which is responsible 
for the preprocessor) and its direct dependencies, which at the 
end amount to libLLVMCore and the C++ standard library, 
shouldn't be too much size overhead (ymmv). The license is 
also ok, since it's a BSD-something.

To also address the issue of how the preprocessor handles 
Haskell tokens in macros, if you import the source someone 
could make a patch to add an option to make the 
preprocessor less strict (but I'm sure to have seen already 
something to opt for a lax semantics when the preprocessor is 
used standalone, need to check that). If done well and 
promised to be maintained, I think the patch could also be 
accepted mainstream (it's not the first time an LLVM project 
accepts GHC specific patches, see the support for its call 
convention in the code generator).

Greetings,
Nicola