Re: [Gretl-devel] c code question

On Sat, 14 Oct 2017, Sven Schreiber wrote: Yes, a good question. Adding a new C function to libgretl is just a matter of... doing just that. You write a function in C, stick into an appropriate .c file in lib/src, and -- if it's supposed to be publicly available (and I don't suppose there would be much point otherwise) -- also add a declaration of the function to the corresponding .h header file. Making such a function accessible via hansl requires working with the C files genparse.h, genlex.c and geneval.c (in lib/src). genparse.h is where you insert a unique internal identifier for the function (e.g. F_NUMHESS), putting it into the functions "enum" in the right place. Scanning the existing enum one should get an idea of what "the right place" means. Basically: how many arguments does the new function take? -- other than that it doesn't much matter where it goes. genlex.c is where you create a mapping from the function's internal identifier (e.g. F_NUMHESS) to the name under which users can call it (e.g. "numhess"). Plenty of examples available there. The exact position of the new entry doesn't matter. geneval.c is where you actually "hook up" the hansl function to its C back-end. A hansl-function must have an entry in the function named "eval". This entry should (usually) do some basic type-checking on the arguments provided by the user, then hand off to an implementer function. The best way to grok this is to follow the path of execution for a hansl function that you're familiar with. Ideally you want to find an existing function that is as similar as possible to your new one, in terms of (a) what it returns, and (b) the type of arguments it expects. I (or Jack) can provide more detail as needed, but that's the basic overview. Allin