4 Calling Procedures (CS)
As an entry point into Racket, C programs should normally call Racket
procedures by using racket_apply, which calls the procedure in
the initial Racket thread of the main Racket place. Chez Scheme entry
points such as Scall0 and Scall directly call a
procedure outside of any Racket thread, which will not work correctly
with Racket facilities such as threads, parameters, continuations, or
The functions in this section are meant to be used as an entry point
to Racket, but not as a re-entry point. When Racket calls a C
function that in turn calls back into Racket, the best approach is to
use the FFI (see The Racket Foreign Interface) so that the C call recieves a
Racket callback that is wrapped as a plain C callback. That way, the
FFI can handle the details of boundary crossings between Racket and C.
Applies the Racket procedure proc to the list of arguments
arg_list. The procedure is called in the original Racket thread
of the main Racket place. Applying proc must not raise an
exception or otherwise escape from the call to proc.
The result is a list of result values, where a single result from
proc causes racket_apply to return a list of length one.
Other Racket threads can run during the call to proc. At the
point that proc results, all Racket thread scheduling in the
main Racket place is suspended. No garbage collections will occur, so
other Racket places can block waiting for garbage collection.
Applies the Chez Scheme procedure proc
to zero, one, two, or
three arguments. Beware that not all Racket procedures are Chez Scheme
procedures. (For example, an instance of a structure type that has
is not a Chez Scheme procedure.)
The procedure is called outside of any Racket thread, and other Racket
threads are not scheduled during the call to proc. A garbage
collection may occur.
Similar to Scall0
, but these functions are used in sequence to
apply a Chez Scheme procedure to an arbitrary number of arguments.
is called with the number of arguments. Then,
each argument is installed with Sput_arg
, where the i
argument indicates the argumenrt position and arg
argument value. Finally, Scall
is called with the procedure and
the number of arguments (which must match the number provided to