Factor Language Blog

For the last two weeks I’ve mostly been working on some C library interface (FFI) improvements. FFI work involves dealing with a lot of platform-specific, arcane, poorly documented details, so it is not the most fun thing to code, but it has to be done. It is not too bad, actually, because I get to learn a lot about OS and CPU architecture. So here are the recent improvements:

• Calling C functions returning structs by value is now supported
• Factor callbacks can return structs by value too
• Support for stdcall callbacks on Windows
• The Linux/ARM port now has working FFI
• The Linux/PPC port now has working FFI

Now with these out of the way, Factor 0.88 is ready for release.

The C library interface is quite complete now. Here is what it already supports:

• Easy to use: no glue code has to be written in C, concise
• Relatively efficient
• Supports both stdcall and cdecl ABIs on Windows (and as of 0.88 this support is complete)
• Integer and floating point parameters, return values
• Automatic conversion for ASCII and UTF16 C string parameters, returns
• Declaring C struct and union types, allocating/deallocating/mutating C data
• Passing struct parameters by reference and value (value struct returns were missing until 0.88)
• Calling C functions indirectly by function pointer
• Callbacks from C to Factor

I’m quite proud of how well it works. There are only a few missing features, and I will be adding all of them in the near future:

• “long long” return values work on 32-bit systems, but not “long long” parameters
• Declaring structs and unions which contain fixed-size value arrays
• Passing floating point parameters on ARM

Apart from these I can’t really think of anything else I could add to the FFI. It really does seem quite complete and portable these days.