Got a clear answer about the handling of if defined. Expanding macros within if defined is non-compliant if cpphs is trying to be a C99 preprocessor: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf 6.10.1/1 Conditional Inclusion pg 148 indicates that the token after defined or within defined ( ) is an identifier, not a macro to be expanded. I'm not sure what's involved in fixing this behavior in cpphs, but I'm happy to test fixes. On Sun, Jan 10, 2016 at 3:53 PM Alain O'Dea wrote:

I've isolated the issue to the handling of if defined on multi-argument macros.

I took a crack at interpreting the cpphs source for this and I think it may be a bug in the conversion of defined expressions here in Language.Preprocessor.CppIfdef here:

convert "defined" [arg] = case lookupST arg st of Nothing | all isDigit arg -> return arg Nothing -> return "0" Just (a@AntiDefined{}) -> return "0" Just (a@SymbolReplacement{}) -> return "1" Just (a@MacroExpansion{}) -> return "1"

It looks like it will macro expand the contents of a defined expression which isn't what GCC does. I don't know if GCC is wrong or if using parameterized macros within

if defined works on single-argument macros.

working1.hs:

{-# LANGUAGE CPP #-}

#define EXAMPLE_MACRO(arg) (\ arg)

#if defined(EXAMPLE_MACRO) #endif

preprocess it (it works!):

$ cpphs --cpp working1.hs -o $tempfile $

ifdef works on multiple-argument macros.

working2.hs:

{-# LANGUAGE CPP #-}

#define EXAMPLE_MACRO(arg1,arg2) (\ arg1 > arg2)

#ifdef EXAMPLE_MACRO #endif

preprocess it (it works!):

$ cpphs --cpp working2.hs -o $tempfile $

if defined fails on multi-argument macros.

broken2.hs:

{-# LANGUAGE CPP #-}

#define EXAMPLE_MACRO(arg1,arg2) (\ arg1 > arg2)

#if defined(EXAMPLE_MACRO) #endif

preprocess it (it fails!):

$ cpphs --cpp broken2.hs -o $tempfile cpphs: macro EXAMPLE_MACRO expected 2 arguments, but was given 0 $

I've posted a StackOverflow question to see if any of them know if this is undefined behavior:

http://stackoverflow.com/questions/34709769/is-cpphs-wrong-or-is-the-behavio...

If it is undefined behavior we should stop relying on it in GHC sources. Either way the behavior is inconsistent with GCC which complicates things.

Best, Alain

On Sun, Jan 10, 2016 at 2:04 PM Alain O'Dea wrote:

...

Hi Malcolm:

cpphs is under consideration as a replacement for GCC's C preprocessor in the GHC toolchain: https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCpp

GHC 7.10.3's build fails when cpphs is used as the C preprocessor (--with-hs-cpp=cpphs --with-hs-cpp-flags="--cpp").

It runs into this error when preprocessing libraries/base/GHC/Natural.hs:

cpphs: macro MIN_VERSION_integer_gmp expected 3 arguments, but was given 0

I've reproduced this issue on Ubuntu 14.04 x86-64 and SmartOS 15.3.0 x86-64.

Interestingly the error seems to arise only when preprocessing Natural.hs while the autogenerated cabal-macros.h is present. Removing that include from the cpphs flags leads to a clean preprocessing run.

I have more details of this investigation here: https://gist.github.com/AlainODea/bd5b3e0e6f7c4227f009

Is this a bug?

Best, Alain

No worries. Thank you Malcolm. If there's anything else I can gather to facilitate the fix let me know. On Sun, Jan 10, 2016 at 5:40 PM Malcolm Wallace wrote:

Thanks for the bug report, and for the detailed analysis. I will try to look at and fix this soon.

Regards, Malcolm

On 10 Jan 2016, at 20:09, Alain O'Dea wrote:

...

Got a clear answer about the handling of if defined.

Expanding macros within if defined is non-compliant if cpphs is trying to be a C99 preprocessor: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf 6.10.1/1 Conditional Inclusion pg 148 indicates that the token after defined or within defined ( ) is an identifier, not a macro to be expanded.

I'm not sure what's involved in fixing this behavior in cpphs, but I'm happy to test fixes.

On Sun, Jan 10, 2016 at 3:53 PM Alain O'Dea wrote: I've isolated the issue to the handling of if defined on multi-argument macros.

I took a crack at interpreting the cpphs source for this and I think it may be a bug in the conversion of defined expressions here in Language.Preprocessor.CppIfdef here:

convert "defined" [arg] = case lookupST arg st of Nothing | all isDigit arg -> return arg Nothing -> return "0" Just (a@AntiDefined{}) -> return "0" Just (a@SymbolReplacement{}) -> return "1" Just (a@MacroExpansion{}) -> return "1"

It looks like it will macro expand the contents of a defined expression which isn't what GCC does. I don't know if GCC is wrong or if using parameterized macros within

if defined works on single-argument macros.

working1.hs:

{-# LANGUAGE CPP #-}

#define EXAMPLE_MACRO(arg) (\ arg)

#if defined(EXAMPLE_MACRO) #endif

preprocess it (it works!):

$ cpphs --cpp working1.hs -o $tempfile $

ifdef works on multiple-argument macros.

working2.hs:

{-# LANGUAGE CPP #-}

#define EXAMPLE_MACRO(arg1,arg2) (\ arg1 > arg2)

#ifdef EXAMPLE_MACRO #endif

preprocess it (it works!):

$ cpphs --cpp working2.hs -o $tempfile $

if defined fails on multi-argument macros.

broken2.hs:

{-# LANGUAGE CPP #-}

#define EXAMPLE_MACRO(arg1,arg2) (\ arg1 > arg2)

#if defined(EXAMPLE_MACRO) #endif

preprocess it (it fails!):

$ cpphs --cpp broken2.hs -o $tempfile cpphs: macro EXAMPLE_MACRO expected 2 arguments, but was given 0 $

I've posted a StackOverflow question to see if any of them know if this is undefined behavior:

http://stackoverflow.com/questions/34709769/is-cpphs-wrong-or-is-the-behavio...

...

If it is undefined behavior we should stop relying on it in GHC

sources. Either way the behavior is inconsistent with GCC which complicates things.

...

Best, Alain

On Sun, Jan 10, 2016 at 2:04 PM Alain O'Dea

...

Hi Malcolm:

cpphs is under consideration as a replacement for GCC's C preprocessor in the GHC toolchain: https://ghc.haskell.org/trac/ghc/wiki/Proposal/NativeCpp

GHC 7.10.3's build fails when cpphs is used as the C preprocessor (--with-hs-cpp=cpphs --with-hs-cpp-flags="--cpp").

It runs into this error when preprocessing libraries/base/GHC/Natural.hs:

cpphs: macro MIN_VERSION_integer_gmp expected 3 arguments, but was given 0

I've reproduced this issue on Ubuntu 14.04 x86-64 and SmartOS 15.3.0 x86-64.

Interestingly the error seems to arise only when preprocessing Natural.hs while the autogenerated cabal-macros.h is present. Removing

wrote: that include from the cpphs flags leads to a clean preprocessing run.

...

I have more details of this investigation here: https://gist.github.com/AlainODea/bd5b3e0e6f7c4227f009

Is this a bug?

Best, Alain