I have just come up against an application where I would like the user to be able (if required) to link in a file containing a set of default options to the application. So what I would IDEALLY like is (1) the ability for FFI to give me access to an external value as well as an external function, as in foreign import "default_arguments" defaultArguments :: Addr
We have this. It's called "foreign label", but it's in an obscure part of the documentation - you're not the first person to miss it :)
(2) the ability for FFI to link in values as weak external references. (In other words the reference doesn't have to be resolved and you can find out if it has been.) So assuming (1) has been implemented, I might want something additionally like foreign import weak "default_arguments" getDefaultArguments :: IO (Maybe Addr) Now while I would LIKE these features, they aren't there, and it won't cause me great distress to work around their absence. But why not implement them anyway?
Do you know how to use existing support for weak references in the linker/assembler? I believe GNU as/ld has them, but I can't find any reference in the docs. Alternatively we'd have to implement this using something like dlsym, which only looks for references in shared libraries. Cheers, Simon