I have a source base that contains a number of source files that use APIs that vary by platform: every platform provides select, most provide poll, BSDs provide kqueue, and Linux provides epoll. I already have autoconf tests for these functions, and I'd like to use the results of those autoconf checks to determine which modules to compile, but I am unable to figure out how to do this in my .cabal or .buildinfo file. (I /could/ have explicit os conditionals in there, but that's ugly.)
Right now, I'm just building all of the modules, and conditionally giving them bodies as follows:
module System.Event.EPoll where #if defined(HAVE_EPOLL) ... #endif
The trouble with this is twofold. I have to export everything in the module (because its contents vary depending on where I compile it), and the CPP macros there are ugly. Is there a better solution? This means that modules with the same name have different set of functions, depending on OS? I think this is generally unsafe, because other packages would have to check what API to expect according to the OS. Whereever possible I try to use conditional Hs-Source-Dirs in Cabal for selecting OS specific modules, but all of the directories must contain
Bryan O'Sullivan schrieb: the same set of module names and modules with the same name must have the same interface. If modules have different APIs then I would give them different names and put them even in different packages. Then, say, presence of package poll-bsd means to the package user, that BSD functionality is available. Whether he is actually running BSD or whether the package simulates BSD functions doesn't matter.