SEXP objects

All functions callable from R must return a SEXP, and only take arguments which are of type SEXP (or just void if there are no arguments).

The SEXP type is an S-Expression. Every value in R is an SEXP, and there is information stored within the type to indicate what data is stored within it.

The TYPEOF() macro and type2char() function within C will be useful to identify what sort of data is in the SEXP.

Listing of all SEXP types

The full list of SEXP types are in Rinternals.h

#define NILSXP       0    /* nil = NULL */
#define SYMSXP       1    /* symbols */
#define LISTSXP      2    /* lists of dotted pairs */
#define CLOSXP       3    /* closures */
#define ENVSXP       4    /* environments */
#define PROMSXP      5    /* promises: [un]evaluated closure arguments */
#define LANGSXP      6    /* language constructs (special lists) */
#define SPECIALSXP   7    /* special forms */
#define BUILTINSXP   8    /* builtin non-special forms */
#define CHARSXP      9    /* "scalar" string type (internal only)*/
#define LGLSXP      10    /* logical vectors */
/* 11 and 12 were factors and ordered factors in the 1990s */
#define INTSXP      13    /* integer vectors */
#define REALSXP     14    /* real variables */
#define CPLXSXP     15    /* complex variables */
#define STRSXP      16    /* string vectors */
#define DOTSXP      17    /* dot-dot-dot object */
#define ANYSXP      18    /* make "any" args work.
                 Used in specifying types for symbol
                 registration to mean anything is okay  */
#define VECSXP      19    /* generic vectors */
#define EXPRSXP     20    /* expressions vectors */
#define BCODESXP    21    /* byte code */
#define EXTPTRSXP   22    /* external pointer */
#define WEAKREFSXP  23    /* weak reference */
#define RAWSXP      24    /* raw bytes */
#define OBJSXP      25    /* object, non-vector  */
#define S4SXP       25    /* same as OBJSXP, retained for back compatability */

/* used for detecting PROTECT issues in memory.c */
#define NEWSXP      30    /* fresh node created in new page */
#define FREESXP     31    /* node released by GC */

#define FUNSXP      99    /* Closure or Builtin or Special */

Code example: Print the SEXP type of an object

#include <R.h>
#include <Rinternals.h>

SEXP what_sexp_is_this(SEXP x) {
  Rprintf("SEXPTYPE: %i = %s\n", TYPEOF(x), type2char(TYPEOF(x)));
  return R_NilValue;
}

Click to show R code

code = r"(
#include <R.h>
#include <Rinternals.h>

SEXP what_sexp_is_this(SEXP x) {
  Rprintf("SEXPTYPE: %i = %s\n", TYPEOF(x), type2char(TYPEOF(x)));
  return R_NilValue;
}                
)"

callme::compile(code)

what_sexp_is_this(1L)
#> SEXPTYPE: 13 = integer
what_sexp_is_this(TRUE)
#> SEXPTYPE: 10 = logical
what_sexp_is_this(c(1.1, 2.2))
#> SEXPTYPE: 14 = double
what_sexp_is_this(list(1, 2, 3))
#> SEXPTYPE: 19 = list
what_sexp_is_this("hello")
#> SEXPTYPE: 16 = character
what_sexp_is_this(mtcars)
#> SEXPTYPE: 19 = list
what_sexp_is_this(mean)
#> SEXPTYPE: 3 = closure