4 ms·

Not really, it's quite easy to call Objective-C methods (or more correctly, to send messages to Objective-C selectors) and perform other Objective-C-related tas

Not really, it's quite easy to call Objective-C methods (or more correctly, to send messages to Objective-C selectors) and perform other Objective-C-related tasks from C. See: https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ObjCRuntimeRef/Reference/reference.html https://developer.apple.com/library/mac/documentation/Cocoa/... This is actually what the Objective-C compiler does. It translates your Objective-C code to C method calls.

chc 13y ago
It's not that easy. I mean, just sending a message could entail one of objc_msgSend, obj_msgSend_stret or objc_msgSend_fpret, and which one you want to use is not always as clear-cut as you might prefer (http://www.sealiesoftware.com/blog/archive/2008/10/30/objc_explain_objc_msgSend_stret.html http://www.sealiesoftware.com/blog/archive/2008/10/30/objc_e...). And then there's the hassle of defining classes dynamically, which entails six function calls just to create a class with one empty method, and one of those essential functions is not actually provided for you AFAIK unless you're using Apple's compiler where it's a builtin, so you'll need to write it yourself. It's not ridiculously hard, but it's somewhat less easy than normal C FFI.
- iand675 13y ago
  The other hard part about it is that Haskell's FFI doesn't support variadic functions in a friendly way, which makes argument passing that much trickier.
  - chc 13y ago
    There is a similar problem with objc_msgSend in C: Methods with certain argument types can't be called with a normal objc_msgSend(). Instead, you need to create a specifically typed function pointer and assign objc_msgSend to it. I think a similar solution would be necessary with Haskell.
    - iand675 13y ago
      I'd appreciate seeing a link to an example of this. I put a decent amount of work (a few years ago) into writing some bindings in Haskell to the objc runtime, but ended up shelving it until I could come up with a satisfactory solution to the variadic function dilemma.
      - chc 13y ago
        Here are a couple of Stack Overflow answers that illustrate how you do it in Objective-C: http://stackoverflow.com/a/2573949 http://stackoverflow.com/a/2573949 http://stackoverflow.com/a/18689338 http://stackoverflow.com/a/18689338 If you're interested in the nitty-gritty of how objc_msgSend works, bbum from Apple wrote up a great low-level walkthrough a few years back: http://www.friday.com/bbum/2009/12/18/objc_msgsend-part-1-the-road-map/ http://www.friday.com/bbum/2009/12/18/objc_msgsend-part-1-th...
  - JoshTriplett 13y ago
    If you just need to call variadic functions with a specific parameter list determined at compile time, that's easy with the existing FFI; just write a prototype for the function for any given set of arguments you want to call it with. (For instance, you can have an FFI binding printf_int_float :: CString -> CInt -> CFloat -> IO CInt .) If you really need to construct calls at runtime and you don't know the argument list at compile time, there's a Haskell binding to libffi. However, you generally only need that if you're writing a language interpreter or similar.

chc 13y ago

It's not that easy. I mean, just sending a message could entail one of objc_msgSend, obj_msgSend_stret or objc_msgSend_fpret, and which one you want to use is not always as clear-cut as you might prefer (http://www.sealiesoftware.com/blog/archive/2008/10/30/objc_explain_objc_msgSend_stret.html http://www.sealiesoftware.com/blog/archive/2008/10/30/objc_e...). And then there's the hassle of defining classes dynamically, which entails six function calls just to create a class with one empty method, and one of those essential functions is not actually provided for you AFAIK unless you're using Apple's compiler where it's a builtin, so you'll need to write it yourself. It's not ridiculously hard, but it's somewhat less easy than normal C FFI.

iand675 13y ago
The other hard part about it is that Haskell's FFI doesn't support variadic functions in a friendly way, which makes argument passing that much trickier.
- chc 13y ago
  There is a similar problem with objc_msgSend in C: Methods with certain argument types can't be called with a normal objc_msgSend(). Instead, you need to create a specifically typed function pointer and assign objc_msgSend to it. I think a similar solution would be necessary with Haskell.
  - iand675 13y ago
    I'd appreciate seeing a link to an example of this. I put a decent amount of work (a few years ago) into writing some bindings in Haskell to the objc runtime, but ended up shelving it until I could come up with a satisfactory solution to the variadic function dilemma.
    - chc 13y ago
      Here are a couple of Stack Overflow answers that illustrate how you do it in Objective-C: http://stackoverflow.com/a/2573949 http://stackoverflow.com/a/2573949 http://stackoverflow.com/a/18689338 http://stackoverflow.com/a/18689338 If you're interested in the nitty-gritty of how objc_msgSend works, bbum from Apple wrote up a great low-level walkthrough a few years back: http://www.friday.com/bbum/2009/12/18/objc_msgsend-part-1-the-road-map/ http://www.friday.com/bbum/2009/12/18/objc_msgsend-part-1-th...
- JoshTriplett 13y ago
  If you just need to call variadic functions with a specific parameter list determined at compile time, that's easy with the existing FFI; just write a prototype for the function for any given set of arguments you want to call it with. (For instance, you can have an FFI binding printf_int_float :: CString -> CInt -> CFloat -> IO CInt .) If you really need to construct calls at runtime and you don't know the argument list at compile time, there's a Haskell binding to libffi. However, you generally only need that if you're writing a language interpreter or similar.