Reading the internal function table

gistfile1.txt

#include <Rcpp.h>
using namespace Rcpp;

typedef SEXP (*CCODE)(SEXP, SEXP, SEXP, SEXP);

/* Information for Deparsing Expressions */
typedef enum {
    PP_INVALID  =  0,
    PP_ASSIGN   =  1,
    PP_ASSIGN2  =  2,
    PP_BINARY   =  3,
    PP_BINARY2  =  4,
    PP_BREAK    =  5,
    PP_CURLY    =  6,
    PP_FOR      =  7,
    PP_FUNCALL  =  8,
    PP_FUNCTION =  9,
    PP_IF 	= 10,
    PP_NEXT 	= 11,
    PP_PAREN    = 12,
    PP_RETURN   = 13,
    PP_SUBASS   = 14,
    PP_SUBSET   = 15,
    PP_WHILE 	= 16,
    PP_UNARY 	= 17,
    PP_DOLLAR 	= 18,
    PP_FOREIGN 	= 19,
    PP_REPEAT 	= 20
} PPkind;

typedef enum {
    PREC_FN	 = 0,
    PREC_LEFT    = 1,
    PREC_EQ	 = 2,
    PREC_RIGHT	 = 3,
    PREC_TILDE	 = 4,
    PREC_OR	 = 5,
    PREC_AND	 = 6,
    PREC_NOT	 = 7,
    PREC_COMPARE = 8,
    PREC_SUM	 = 9,
    PREC_PROD	 = 10,
    PREC_PERCENT = 11,
    PREC_COLON	 = 12,
    PREC_SIGN	 = 13,
    PREC_POWER	 = 14,
    PREC_DOLLAR  = 15,
    PREC_NS	 = 16,
    PREC_SUBSET	 = 17
} PPprec;

typedef struct {
	PPkind kind; 	 /* deparse kind */
	PPprec precedence; /* operator precedence */
	unsigned int rightassoc;  /* right associative? */
} PPinfo;

typedef struct {
    char   *name;    /* print name */
    CCODE  cfun;     /* c-code address */
    int	   code;     /* offset within c-code */
    int	   eval;     /* evaluate args? */
    int	   arity;    /* function arity */
    PPinfo gram;     /* pretty-print info */
} FUNTAB;

extern FUNTAB	R_FunTab[];	    /* Built in functions */ 

CCODE get_internal( std::string name){
    FUNTAB* p = R_FunTab ;
    for( ; p->name != NULL; ++p ){
        Rprintf( "%s\n", p->name ) ;
        if( name == p->name )
            return p->cfun ;
    }
    return NULL ;
}

// [[Rcpp::export]]
SEXP internal_rank( SEXP x){
    CCODE rank_fun = get_internal( "rank" );
    Language call( "rank", x, Rf_length(x), "average" ) ;    
    return rank_fun(call, Rf_ScalarInteger(0), CDR(call), R_GlobalEnv ) ; 
}


/*** R
    internal_rank(rnorm(10))
*/