There are plenty of macros that only check for GNU GCC and don't bother checking support from other popular compilers. For example, in libguile/__scm.h, the macros SCM_NORETURN, SCM_UNUSED, SCM_EXPECT, and many more, all only check for GCC support. Most (if not all) of these language extensions are supported by Clang, and usually using the same exact syntax! I'll submit a patch that adds Clang support to these macros. See < http://clang.llvm.org/docs/LanguageExtensions.html> for the documentation about this. -- Matt Sicker