I've got a piece of code that looks like this: baselineContextSSL :: IO SSLContext baselineContextSSL = do ctx <- SSL.context SSL.contextSetDefaultCiphers ctx #if defined __MACOSX__ SSL.contextSetVerificationMode ctx SSL.VerifyNone #elif defined __WIN32__ SSL.contextSetVerificationMode ctx SSL.VerifyNone #else SSL.contextSetCADirectory ctx "/etc/ssl/certs" SSL.contextSetVerificationMode ctx $ SSL.VerifyPeer True True Nothing #endif return ctx all very nice (this being necessary because apparently the non-free operating systems don't store their certs in a reliably discoverable place; bummer). That, however, is not the problem. After all, this sort of thing is what #ifdefs are for. The problem is needing to get an appropriate symbol based on what OS you're using defined. I naively assumed there would be __LINUX__ and __MACOSX__ and __WIN32__ defined by GHC because, well, that's just the sort of wishful thinking that powers the universe. So my question is: what's an appropriate Haskell mechanism for building code that is OS / arch / distro specific? It's not like I have autoconf running generating me a config.h I could #include, right? This feels simple and an appropriate use of CPP; even the symbol names look just about like what I would have expected; stackoverflow said so, must be true. Just need to get the right symbol defined at build time. Any suggestions? AfC Sydney