Re: Using stringize and string concatenation in ghc preprocessing

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Re: Using stringize and string concatenation in ghc preprocessing

Boespflug, Mathieu
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 <[hidden email]> wrote:
On Sat, Aug 20, 2016 at 2:27 PM, Harendra Kumar <[hidden email]> 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
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Re: Using stringize and string concatenation in ghc preprocessing

Brandon Allbery
On Sun, Aug 21, 2016 at 4:31 PM, Boespflug, Mathieu <[hidden email]> wrote:
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
 
.

That's the hacky K&R way I mentioned earlier.

--
brandon s allbery kf8nh                               sine nomine associates
[hidden email]                                  [hidden email]
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net

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Re: Using stringize and string concatenation in ghc preprocessing

Harendra Kumar
In reply to this post by Boespflug, Mathieu
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 <[hidden email]> 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 <[hidden email]> wrote:
On Sat, Aug 20, 2016 at 2:27 PM, Harendra Kumar <[hidden email]> 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
[hidden email]                                  [hidden email]
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net

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[hidden email]
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