Thanks, Xiao.

I'm closing this this issue, because the patch is already merged.

Hi Florian,

I'm happy to help, will get back to you later.

Hi Malte,

I don't recall what's error when I compiled the codebase with clang. It probably was 
same error.

I just pulled the latest changes and compiled with clang.
Everything is good.
This really makes anyone using Mac OS much easier to try out Fast-Downward, thank you 
for the effort.

Also, I read in your link that you use XCode. CMake can theoretically generate
an XCode project for you and I would also be interested in how this works out.

Hi Xiao,

we are also currently working on a new build system based on cmake (issue67).
I'm currently looking for volunteers to test this with as many different setups
as possible. As Malte said, we don't have Macs, so we didn't test it there so
far. If you want to help with this, you could clone from my repository, update
to the branch, try to build and run everything, and report the results in
issue67 (msg4431 and msg4434 in issue67 explain how to do this).

Dear Xiao, thanks for reporting this!

We cannot move the #include on top of the #if block because this would break the
build on Windows. I have instead added the #include into the part of the #if
statement for Mac OS as well. Can you test if the newest version of the code
works for you?

Also, regarding the documentation, we made some changes to make the code compile
with clang as well, so I'm not sure the additional setup setups mentioned in our
current build instructions are necessary. Would it be possible for you to try
out what happens if you just try to build the compiler with "./build_all" with
no further options? (Unfortunately we don't have access to a Mac ourselves.)

I got the following error while compiling the code on MacOS with gcc 4.8.
utilities.cc:174:12: error: use of undeclared identifier 'getpid'
    return getpid();
           ^
1 error generated.
make: *** [.obj/utilities.release.o] Error 1


It can be fixed by moving "#include <unistd.h>" to above "#if OPERATING_SYSTEM == LINUX" in the file 
"src/search/utilities.cc"

Detail steps I tried compiling on Mac OSX: https://xli.github.io/ai/2015/07/28/compile-fast-
downward-on-mac-osx.html

(This is a tiny problem for me, and I don't really need the fix. Just thought you may like to know 
this and simply fix it)