Thanks Mathieu. This works pretty well for gcc ( https://gcc.gnu.org/onlinedocs/cpp/Traditional-macros.html) but sadly it does not work for clang cpp as Brandon too pointed out earlier that clang does not have a traditional mode. -harendra On 22 August 2016 at 02:01, Boespflug, Mathieu wrote:

Hi Harendra,

I ran into this very problem recently. Turns out -traditional knows string concatenation too. I seem to remember learning this by browsing the GHC source code, but now I can't find any occurrence of this pattern. But here's an example of how to do string concatenation with CPP in -traditional mode: https://github.com/tweag/sparkle/blob/ a4e481aa5180b6ec93c219f827aefe932b66a953/inline-java/src/ Foreign/JNI.hs#L274.

HTH,

-- Mathieu Boespflug Founder at http://tweag.io.

On 20 August 2016 at 20:33, Brandon Allbery wrote:

...

On Sat, Aug 20, 2016 at 2:27 PM, Harendra Kumar

...

wrote:

...

But "-optP" seems to only append to the flags that GHC already passes and gcc has no "-no-traditional" option to undo the effect of the "-traditional" that GHC has already passed. I think "-optP" should override the flags passed by ghc rather than appending to them. Is there a reason not to do that?

Is there any other better way to achieve this? What is the standard way of doing this if any?

Removing -traditional will break much Haskell source. Go look at the history of clang with ghc (clang doesn't do -traditional) to see what happens. (tl;dr: without -traditional, cpp knows too much about what constitutes valid C, and mangles and/or throws errors on valid Haskell that doesn't lex the way C does.)

You might want to look at cpphs as an alternative preprocessor. There are some ancient K&R-era hacks that could be used if absolutely necessary, but cpphs should be a much simpler and cleaner solution.

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

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