chickadee » foreign » access » foreign-primitive

This is also similar to foreign-lambda* but the code will be executed in a primitive CPS context, which means it will not actually return, but call its continuation on exit. This means that code inside this form may allocate Scheme data on the C stack (the nursery) with C_alloc (see below). You can return multiple values inside the body of the foreign-primitive form by using the following C code:

C_word av[N + 2] = { C_SCHEME_UNDEFINED, C_k, X1, ... };
C_values(N + 2, av);

where N is the number of values to be returned, and X1, ... are the results, which should be Scheme data objects. When returning multiple values, the return-type should be omitted. Of course, if you have to dynamically compute the values, you do not have to use C's array initialization syntax, but you can just assign them one by one.

Returning just a single value can still be done via the C_return(...) macro.