example of using named arguments and ... in R's C API

R_C_example1.c

SEXP call_function(SEXP call, SEXP rho){

  /* advance to 2nd element (CAR) of call pairlist; 1st element is just the call_function function */
  SEXP args = CDR(call);

  /* get function (2rd element) and advance to 3th element */
  SEXP funSymbol = install("FUN");
  args = CDR(args);

  /* make the function call */
  SEXP R_fcall;
  PROTECT(R_fcall = LCONS(funSymbol, LCONS(R_DotsSymbol,R_NilValue)));
  
  /* call the function */
  R_forceAndCall(R_fcall, 1, rho);

  UNPROTECT(1);
  return R_NilValue;
}

static R_CallMethodDef callMethods[]  = {
  {"C_call_function", (DL_FUNC)&call_function, 2},
  {NULL, NULL, 0}
};

void R_init_envestigate(DllInfo *info){
  R_registerRoutines(info, NULL, callMethods, NULL, NULL);
}

/* In R ... (must be properly done in a package)
 *
 * #' call_function
 * #' @name call_function
 * #' @export
 * #' @useDynLib myPackage C_call_function
 * #'
 * call_function <- function(FUN,...){
 *  call <- match.call(expand.dots = FALSE)
 *  .Call(C_call_function,call,environment())
 * }
 * 
 * nest = function(z){cat("im nested! im printing z! ",z,"\n")}
 * call_function(FUN = function(x=2,y=3,...){print(x);print(y);nest(...)},z=1)
 *
 *
 *
*/