14 Procedures (BC)
A primitive procedure is a Racket-callable procedure that is
implemented in C. Primitive procedures are created in Racket with
the function scheme_make_prim_w_arity, which takes a C function
pointer, the name of the primitive, and information about the number
of Racket arguments that it takes; it returns a Racket procedure
The C function implementing the procedure must take two arguments: an
integer that specifies the number of arguments passed to the
procedure, and an array of Scheme_Object* arguments. The number
of arguments passed to the function will be checked using the arity
information. (The arity information provided to
scheme_make_prim_w_arity is also used for the Racket
arity procedure.) The procedure implementation is not allowed
to mutate the input array of arguments; as an exception, the procedure
can mutate the array if it is the same as the result of
scheme_current_argument_stack. The procedure may mutate the
arguments themselves when appropriate (e.g., a fill in a vector
The function scheme_make_prim_closure_w_arity is similar to
scheme_make_prim_w_arity, but it takes an additional count and
Scheme_Object* array that is copied into the created procedure;
the procedure is passed back to the C function when the closure is
invoked. In this way, closure-like data from the C world can be
associated with the primitive procedure.
The function scheme_make_closed_prim_w_arity is similar to
scheme_make_prim_closure_w_arity, but it uses an older calling
convention for passing closure data.
To work well with Scheme threads, a C function that performs
substantial or unbounded work should occasionally call
SCHEME_USE_FUEL; see Allowing Thread Switches for details.
Creates a primitive procedure value, given the C function pointer
prim. The form of prim is defined by:
typedef Scheme_Object *(Scheme_Prim)(int argc,
The value mina should be the minimum number of arguments that
must be supplied to the procedure. The value maxa should be the
maximum number of arguments that can be supplied to the procedure, or
-1 if the procedure can take arbitrarily many arguments. The
mina and maxa values are used for automatically checking
the argument count before the primitive is invoked, and also for the
Racket arity procedure. The name argument is
used to report application arity errors at run-time.
Same as scheme_make_prim_w_arity
, but the arity is (0, -1) and the
name “UNKNOWN” is assumed. This function is provided for backward
Creates a primitive procedure value that includes the c values
in vals; when the C function prim is invoked, the
generated primitive is passed as the last parameter. The form of
prim is defined by:
Scheme_Object *(Scheme_Prim_Closure_Proc)(int argc,
The macro SCHEME_PRIM_CLOSURE_ELS takes a primitive-closure
object and returns an array with the same length and content as
vals. (3m: see Cooperating with 3m for a caution about
Creates an old-style primitive procedure value; when the C function
prim is invoked, data is passed as the first parameter.
The form of prim is defined by:
Scheme_Object *(Scheme_Closed_Prim)(void *data, int argc,
Creates a closed primitive procedure value without arity information.
This function is provided for backward compatibility only.
Returns a pointer to an internal stack for argument passing. When the
argument array passed to a procedure corresponds to the current
argument stack address, the procedure is allowed to modify the
array. In particular, it might clear out pointers in the argument
array to allow the arguments to be reclaimed by the memory manager (if
they are not otherwise accessible).