The R Project SVN R

/*
 *  R : A Computer Language for Statistical Data Analysis
 *  Copyright (C) 1995, 1996  Robert Gentleman and Ross Ihaka
 *  Copyright (C) 1997--2000  Robert Gentleman, Ross Ihaka and the
 *                            R Development Core Team
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <Defn.h>
#include <Rmath.h>

static void checkNames(SEXP, SEXP);
static SEXP installAttrib(SEXP, SEXP, SEXP);
static SEXP removeAttrib(SEXP, SEXP);

SEXP comment(SEXP);
static SEXP commentgets(SEXP, SEXP);

static SEXP stripAttrib(SEXP tag, SEXP lst)
{
    if(lst == R_NilValue) return lst;
    if(tag == TAG(lst)) return stripAttrib(tag, CDR(lst));
    SETCDR(lst, stripAttrib(tag, CDR(lst)));
    return lst;
}

SEXP getAttrib(SEXP vec, SEXP name)
{
    SEXP s;
    int len, i, any;

    /* pre-test to avoid expensive operations if clearly not needed -- LT */
    if (ATTRIB(vec) == R_NilValue &&
    ! (TYPEOF(vec) == LISTSXP || TYPEOF(vec) == LANGSXP))
    return R_NilValue;

    if (isString(name)) name = install(CHAR(STRING_ELT(name, 0)));

    if (name == R_NamesSymbol) {
    if(isVector(vec) || isList(vec) || isLanguage(vec)) {
        s = getAttrib(vec, R_DimSymbol);
        if(TYPEOF(s) == INTSXP && length(s) == 1) {
        s = getAttrib(vec, R_DimNamesSymbol);
                if(!isNull(s)) {
                    SET_NAMED(VECTOR_ELT(s, 0), 2);
                    return VECTOR_ELT(s, 0);
                }
        }
    }
    if (isList(vec) || isLanguage(vec)) {
        len = length(vec);
        PROTECT(s = allocVector(STRSXP, len));
        i = 0;
        any = 0;
        for ( ; vec != R_NilValue; vec = CDR(vec), i++) {
        if (TAG(vec) == R_NilValue)
            SET_STRING_ELT(s, i, R_BlankString);
        else if (isSymbol(TAG(vec))) {
            any = 1;
            SET_STRING_ELT(s, i, PRINTNAME(TAG(vec)));
        }
        else
            error("getAttrib: invalid type for TAG");
        }
        UNPROTECT(1);
        if (any) {
        if (!isNull(s)) SET_NAMED(s, 2);
        return (s);
        }
        return R_NilValue;
    }
    }
    /* This is where the old/new list ajustment happens. */
    for (s = ATTRIB(vec); s != R_NilValue; s = CDR(s))
    if (TAG(s) == name) {
        if (name == R_DimNamesSymbol && TYPEOF(CAR(s)) == LISTSXP) {
        SEXP new, old;
        int i;
        new = allocVector(VECSXP, length(CAR(s)));
        old = CAR(s);
        i = 0;
        while (old != R_NilValue) {
            SET_VECTOR_ELT(new, i++, CAR(old));
            old = CDR(old);
        }
        SET_NAMED(new, 2);
        return new;
        }
        SET_NAMED(CAR(s), 2);
        return CAR(s);
    }
    return R_NilValue;
}

SEXP setAttrib(SEXP vec, SEXP name, SEXP val)
{
    if (isString(name))
    name = install(CHAR(STRING_ELT(name, 0)));
    if (val == R_NilValue)
    return removeAttrib(vec, name);

    if (vec == R_NilValue)
    error("attempt to set an attribute on NULL");

    PROTECT(vec);
    PROTECT(name);
    val = duplicate(val);
    UNPROTECT(2);

    if (name == R_NamesSymbol)
    return namesgets(vec, val);
    else if (name == R_DimSymbol)
    return dimgets(vec, val);
    else if (name == R_DimNamesSymbol)
    return dimnamesgets(vec, val);
    else if (name == R_ClassSymbol)
    return classgets(vec, val);
    else if (name == R_TspSymbol)
    return tspgets(vec, val);
    else if (name == R_CommentSymbol)
    return commentgets(vec, val);
    else
    return installAttrib(vec, name, val);
}

/* This is called in the case of binary operations to copy */
/* most attributes from (one of) the input arguments to */
/* the output.  Note that the Dim and Names attributes */
/* should have been assigned elsewhere. */

void copyMostAttrib(SEXP inp, SEXP ans)
{
    SEXP s;
    PROTECT(ans);
    PROTECT(inp);
    for (s = ATTRIB(inp); s != R_NilValue; s = CDR(s)) {
    if ((TAG(s) != R_NamesSymbol) &&
        (TAG(s) != R_DimSymbol) &&
        (TAG(s) != R_DimNamesSymbol)) {
        installAttrib(ans, TAG(s), CAR(s));
    }
    }
    SET_OBJECT(ans, OBJECT(inp));
    UNPROTECT(2);
}

static SEXP installAttrib(SEXP vec, SEXP name, SEXP val)
{
    SEXP s, t;
    if (vec == R_NilValue)
    error("attempt to set an attribute on NULL");
    PROTECT(vec);
    PROTECT(name);
    PROTECT(val);
    for (s = ATTRIB(vec); s != R_NilValue; s = CDR(s)) {
    if (TAG(s) == name) {
        SETCAR(s, val);
        UNPROTECT(3);
        return val;
    }
    }
    s = allocList(1);
    SETCAR(s, val);
    SET_TAG(s, name);
    if (ATTRIB(vec) == R_NilValue)
    SET_ATTRIB(vec, s);
    else {
    t = nthcdr(ATTRIB(vec), length(ATTRIB(vec)) - 1);
    SETCDR(t, s);
    }
    UNPROTECT(3);
    return val;
}

static SEXP removeAttrib(SEXP vec, SEXP name)
{
    SEXP t;
    if (name == R_NamesSymbol && isList(vec)) {
    for (t = vec; t != R_NilValue; t = CDR(t))
        SET_TAG(t, R_NilValue);
    return R_NilValue;
    }
    else {
    if (name == R_DimSymbol)
        SET_ATTRIB(vec, stripAttrib(R_DimNamesSymbol, ATTRIB(vec)));
    SET_ATTRIB(vec, stripAttrib(name, ATTRIB(vec)));
    if (name == R_ClassSymbol)
        SET_OBJECT(vec, 0);
    }
    return R_NilValue;
}

static void checkNames(SEXP x, SEXP s)
{
    if (isVector(x) || isList(x) || isLanguage(x)) {
    if (!isVector(s) && !isList(s))
        error("invalid type for names: must be vector");
    if (length(x) != length(s))
        error("names attribute must be the same length as the vector");
    }
    else error("names applied to non-vector");
}


/* Time Series Parameters */

static void badtsp()
{
    error("invalid time series parameters specified");
}

SEXP tspgets(SEXP vec, SEXP val)
{
    double start, end, frequency;
    int n;

    if (!isNumeric(val) || length(val) != 3)
    error("tsp attribute must be numeric of length three");

    if (isReal(val)) {
    start = REAL(val)[0];
    end = REAL(val)[1];
    frequency = REAL(val)[2];
    }
    else {
    start = (INTEGER(val)[0] == NA_INTEGER) ?
        NA_REAL : INTEGER(val)[0];
    end = (INTEGER(val)[1] == NA_INTEGER) ?
        NA_REAL : INTEGER(val)[1];
    frequency = (INTEGER(val)[2] == NA_INTEGER) ?
        NA_REAL : INTEGER(val)[2];
    }
    if (frequency <= 0) badtsp();
    n = nrows(vec);
    if (n == 0) error("cannot assign `tsp' to zero-length vector");
    if (fabs(end - start - (n - 1)/frequency) > 1.e-5)
    badtsp();

    PROTECT(vec);
    val = allocVector(REALSXP, 3);
    PROTECT(val);
    REAL(val)[0] = start;
    REAL(val)[1] = end;
    REAL(val)[2] = frequency;
    installAttrib(vec, R_TspSymbol, val);
    UNPROTECT(2);
    return vec;
}

static SEXP commentgets(SEXP vec, SEXP comment)
{
    if (isNull(comment) || isString(comment)) {
    if (length(comment) <= 0) {
        SET_ATTRIB(vec, stripAttrib(R_CommentSymbol, vec));
    }
    else {
        installAttrib(vec, R_CommentSymbol, comment);
    }
    return R_NilValue;
    }
    error("attempt to set invalid comment attribute");
    return R_NilValue;/*- just for -Wall */
}

SEXP do_commentgets(SEXP call, SEXP op, SEXP args, SEXP env)
{
    checkArity(op, args);
    if (NAMED(CAR(args)) == 2) SETCAR(args, duplicate(CAR(args)));
    if (length(CADR(args)) == 0) SETCADR(args, R_NilValue);
    setAttrib(CAR(args), R_CommentSymbol, CADR(args));
    return CAR(args);
}

SEXP do_comment(SEXP call, SEXP op, SEXP args, SEXP env)
{
    checkArity(op, args);
    return getAttrib(CAR(args), R_CommentSymbol);
}

SEXP classgets(SEXP vec, SEXP class)
{
    if (isNull(class) || isString(class)) {
    if (length(class) <= 0) {
        SET_ATTRIB(vec, stripAttrib(R_ClassSymbol, vec));
        SET_OBJECT(vec, 0);
    }
    else {
        /* When data frames where a special data type */
        /* we had more exhaustive checks here.  Now that */
        /* use JMCs interpreted code, we don't need this */
        /* FIXME : The whole "classgets" may as well die. */
        installAttrib(vec, R_ClassSymbol, class);
        SET_OBJECT(vec, 1);
    }
    return R_NilValue;
    }
    error("attempt to set invalid class attribute");
    return R_NilValue;/*- just for -Wall */
}

SEXP do_classgets(SEXP call, SEXP op, SEXP args, SEXP env)
{
    checkArity(op, args);
    if (NAMED(CAR(args)) == 2) SETCAR(args, duplicate(CAR(args)));
    if (length(CADR(args)) == 0) SETCADR(args, R_NilValue);
    setAttrib(CAR(args), R_ClassSymbol, CADR(args));
    return CAR(args);
}

SEXP do_class(SEXP call, SEXP op, SEXP args, SEXP env)
{
    checkArity(op, args);
    return getAttrib(CAR(args), R_ClassSymbol);
}

/* names(object) <- name */
SEXP do_namesgets(SEXP call, SEXP op, SEXP args, SEXP env)
{
    checkArity(op, args);
    if (NAMED(CAR(args)) == 2)
        SETCAR(args, duplicate(CAR(args)));
    if (CADR(args) != R_NilValue) {
        PROTECT(call = allocList(2));
        SET_TYPEOF(call, LANGSXP);
        SETCAR(call, install("as.character"));
        SETCADR(call, CADR(args));
        SETCADR(args, eval(call, env));
        UNPROTECT(1);
    }
    setAttrib(CAR(args), R_NamesSymbol, CADR(args));
    return CAR(args);
}

SEXP namesgets(SEXP vec, SEXP val)
{
    int i;
    SEXP s, rval;

    PROTECT(vec);
    PROTECT(val);

    /* Ensure that the labels are indeed */
    /* a vector of character strings */

    if (isList(val)) {
    if (!isVectorizable(val))
        error("incompatible names argument");
    else {
        rval = allocVector(STRSXP, length(vec));
        PROTECT(rval);
        for (i = 0; i < length(vec); i++) {
        s = coerceVector(CAR(val), STRSXP);
        SET_STRING_ELT(rval, i, STRING_ELT(s, 0));
        }
        UNPROTECT(1);
        val = rval;
    }
    } else val = coerceVector(val, STRSXP);
    UNPROTECT(1);
    PROTECT(val);

    /* Check that the lengths and types are compatible */

    checkNames(vec, val);

    /* Special treatment for one dimensional arrays */

    if (isVector(vec) || isList(vec) || isLanguage(vec)) {
    s = getAttrib(vec, R_DimSymbol);
    if (TYPEOF(s) == INTSXP && length(s) == 1) {
        PROTECT(val = CONS(val, R_NilValue));
        setAttrib(vec, R_DimNamesSymbol, val);
        UNPROTECT(3);
        return vec;
    }
    }

    /* Cons-cell based objects */

    if (isList(vec) || isLanguage(vec)) {
    i=0;
    for (s = vec; s != R_NilValue; s = CDR(s), i++)
        if (STRING_ELT(val, i) != R_NilValue
        && STRING_ELT(val, i) != R_NaString
        && *CHAR(STRING_ELT(val, i)) != 0)
        SET_TAG(s, install(CHAR(STRING_ELT(val, i))));
        else
        SET_TAG(s, R_NilValue);
    }
    else if (isVector(vec))
    installAttrib(vec, R_NamesSymbol, val);
    else
    error("invalid type to set names attribute");
    UNPROTECT(2);
    return vec;
}

SEXP do_names(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP s;
    checkArity(op, args);
    s = CAR(args);
    if (isVector(s) || isList(s) || isLanguage(s))
    return getAttrib(s, R_NamesSymbol);
    return R_NilValue;
}

SEXP do_dimnamesgets(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP ans;
    if (DispatchOrEval(call, "dimnames<-", args, env, &ans, 0))
    return(ans);
    PROTECT(args = ans);
    checkArity(op, args);
    if (NAMED(CAR(args)) > 2) SETCAR(args, duplicate(CAR(args)));
    setAttrib(CAR(args), R_DimNamesSymbol, CADR(args));
    UNPROTECT(1);
    return CAR(args);
}

SEXP dimnamesgets(SEXP vec, SEXP val)
{
    SEXP dims, top;
    int i, k;

    PROTECT(vec);
    PROTECT(val);

    if (!isArray(vec) && !isList(vec))
    error("dimnames applied to non-array");
    /* This is probably overkill, but you never know; */
    /* there may be old pair-lists out there */
    if (!isPairList(val) && !isNewList(val))
    error("dimnames must be a list");
    dims = getAttrib(vec, R_DimSymbol);
    if ((k = LENGTH(dims)) != length(val))
    error("length of dimnames must match that of dims");
    /* Old list to new list */
    if (isList(val)) {
    SEXP newval;
    newval = allocVector(VECSXP, k);
    for (i = 0; i < k; i++) {
        SET_VECTOR_ELT(newval, i, CAR(val));
        val = CDR(val);
    }
    UNPROTECT(1);
    PROTECT(val = newval);
    }
    for (i = 0; i < k; i++) {
    if (VECTOR_ELT(val, i) != R_NilValue) {
        if (!isVector(VECTOR_ELT(val, i)))
        error("invalid type for dimname (must be a vector)");
        if (INTEGER(dims)[i] != LENGTH(VECTOR_ELT(val, i))
        && LENGTH(VECTOR_ELT(val, i)) != 0)
        error("length of dimnames[%d] not equal to array extent",i+1);
        if (LENGTH(VECTOR_ELT(val, i)) == 0) {
        SET_VECTOR_ELT(val, i, R_NilValue);
        }
        else if (!isString(VECTOR_ELT(val, i))) {
        SET_VECTOR_ELT(val, i,
                   coerceVector(VECTOR_ELT(val, i), STRSXP));
        }
    }
    }
    installAttrib(vec, R_DimNamesSymbol, val);
    if (isList(vec) && k == 1) {
    top = VECTOR_ELT(val, 0);
    i = 0;
    for (val = vec; !isNull(val); val = CDR(val))
        SET_TAG(val, install(CHAR(STRING_ELT(top, i++))));
    }
    UNPROTECT(2);
    return (vec);
}

SEXP do_dimnames(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP ans;
    if (DispatchOrEval(call, "dimnames", args, env, &ans, 0))
    return(ans);
    PROTECT(args = ans);
    checkArity(op, args);
    ans = getAttrib(CAR(args), R_DimNamesSymbol);
    UNPROTECT(1);
    return ans;
}

SEXP do_dim(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP ans;
    if (DispatchOrEval(call, "dim", args, env, &ans, 0))
    return(ans);
    PROTECT(args = ans);
    checkArity(op, args);
    ans = getAttrib(CAR(args), R_DimSymbol);
    UNPROTECT(1);
    return ans;
}

SEXP do_dimgets(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP ans;
    if (DispatchOrEval(call, "dim<-", args, env, &ans, 0))
    return(ans);
    PROTECT(args = ans);
    checkArity(op, args);
    if (NAMED(CAR(args)) > 1) SETCAR(args, duplicate(CAR(args)));
    setAttrib(CAR(args), R_DimSymbol, CADR(args));
    setAttrib(CAR(args), R_NamesSymbol, R_NilValue);
    UNPROTECT(1);
    return CAR(args);
}

SEXP dimgets(SEXP vec, SEXP val)
{
    int len, ndim, i, total;
    PROTECT(vec);
    PROTECT(val);
    if (!isVector(vec) && !isList(vec))
    error("dim<- : invalid first argument");

    if (!isVector(val) && !isList(val))
    error("dim<- : invalid second argument");
    val = coerceVector(val, INTSXP);
    UNPROTECT(1);
    PROTECT(val);

    len = length(vec);
    ndim = length(val);
    if (ndim == 0)
    error("dim: Invalid dimension vector");
    total = 1;
    for (i = 0; i < ndim; i++)
    total *= INTEGER(val)[i];
    if (total != len)
    error("dim<- length of dims do not match the length of object");
    removeAttrib(vec, R_DimNamesSymbol);
    installAttrib(vec, R_DimSymbol, val);
    UNPROTECT(2);
    return vec;
}

SEXP do_attributes(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP attrs, names, namesattr, value;
    int nvalues;
    namesattr = R_NilValue;
    attrs = ATTRIB(CAR(args));
    nvalues = length(attrs);
    if (isList(CAR(args))) {
    namesattr = getAttrib(CAR(args), R_NamesSymbol);
    if (namesattr != R_NilValue)
        nvalues++;
    }
    /* FIXME */
    if (nvalues <= 0)
    return R_NilValue;
    /* FIXME */
    PROTECT(value = allocVector(VECSXP, nvalues));
    PROTECT(names = allocVector(STRSXP, nvalues));
    nvalues = 0;
    if (namesattr != R_NilValue) {
    SET_VECTOR_ELT(value, nvalues, namesattr);
    SET_STRING_ELT(names, nvalues, PRINTNAME(R_NamesSymbol));
    nvalues++;
    }
    while (attrs != R_NilValue) {
    SET_VECTOR_ELT(value, nvalues, CAR(attrs));
    if (TAG(attrs) == R_NilValue)
        SET_STRING_ELT(names, nvalues, R_BlankString);
    else
        SET_STRING_ELT(names, nvalues, PRINTNAME(TAG(attrs)));
    attrs = CDR(attrs);
    nvalues++;
    }
    setAttrib(value, R_NamesSymbol, names);
    SET_NAMED(value, NAMED(CAR(args)));
    UNPROTECT(2);
    return value;
}

/* attributes(object) <- attrs */
SEXP do_attributesgets(SEXP call, SEXP op, SEXP args, SEXP env)
{
/* NOTE: The following code ensures that when an attribute list */
/* is attached to an object, that the "dim" attibute is always */
/* brought to the front of the list.  This ensures that when both */
/* "dim" and "dimnames" are set that the "dim" is attached first. */

    SEXP object, attrs, names;
    int i, nattrs;

    /* If there are multiple references to the object being mutated, */
    /* we must duplicate so that the other references are unchanged. */

    if (NAMED(CAR(args)) == 2)
    SETCAR(args, duplicate(CAR(args)));

    /* Extract the arguments from the argument list */

    object = CAR(args);
    attrs = CADR(args);
    if (object == R_NilValue) {
    if (attrs == R_NilValue)
        return R_NilValue;
    else
        PROTECT(object = allocVector(VECSXP, 0));
    }
    else PROTECT(object);

    if (!isNewList(attrs))
    errorcall(call, "attributes must be in a list");

    /* Empty the existing attribute list */

    /* FIXME: the code below treats pair-based structures */
    /* in a special way.  This can probably be dropped down */
    /* the road (users should never encounter pair-based lists). */
    /* Of course, if we want backward compatibility we can't */
    /* make the change. :-( */

    if (isList(object))
    setAttrib(object, R_NamesSymbol, R_NilValue);
    SET_ATTRIB(object, R_NilValue);
    SET_OBJECT(object, 0);

    /* We do two passes through the attributes; the first */
    /* finding and transferring "dim"s and the second */
    /* transferring the rest.  This is to ensure that */
    /* "dim" occurs in the attribute list before "dimnames". */

    nattrs = length(attrs);
    if (nattrs > 0) {
    names = getAttrib(attrs, R_NamesSymbol);
    if (names == R_NilValue)
        errorcall(call, "attributes must be named");
    for (i = 0; i < nattrs; i++) {
        if (STRING_ELT(names, i) == R_NilValue ||
        CHAR(STRING_ELT(names, i))[0] == '\0') {
        errorcall(call, "all attributes must have names [%d]",i);
        }
        if (!strcmp(CHAR(STRING_ELT(names, i)), "dim"))
        setAttrib(object, R_DimSymbol, VECTOR_ELT(attrs, i));
    }
    for (i = 0; i < nattrs; i++) {
        if (strcmp(CHAR(STRING_ELT(names, i)), "dim"))
        setAttrib(object, install(CHAR(STRING_ELT(names, i))),
              VECTOR_ELT(attrs, i));
    }
    }
    UNPROTECT(1);
    return object;
}

/*  This code replaces an R function defined as

    attr <- function (x, which) 
    {
        if (!is.character(which)) 
            stop("attribute name must be of mode character")
        if (length(which) != 1) 
            stop("exactly one attribute name must be given")
        attributes(x)[[which]]
   }

The R functions was being called very often and replacing it by
something more efficient made a noticeable difference on several
benchmarks.  There is still some inefficiency since using getAttrib
means the attributes list will be searched twice, but this seems
fairly minor.  LT */

SEXP do_attr(SEXP call, SEXP op, SEXP args, SEXP env)
{
    SEXP s, t, tag = R_NilValue, alist;
    char *str;
    int n;
    enum { NONE, PARTIAL, FULL } match = NONE;

    s = CAR(args);
    t = CADR(args);

    if (!isString(t))
    error("attribute name must be of mode character");
    if (length(t) != 1)
    error("exactly one attribute name must be given");

    str = CHAR(STRING_ELT(t, 0));
    n = strlen(str);

    /* try to find a match among the attributes list */
    for (alist = ATTRIB(s); alist != R_NilValue; alist = CDR(alist)) {
    SEXP tmp = TAG(alist);
    if (! strncmp(CHAR(PRINTNAME(tmp)), str, n)) {
        if (strlen(CHAR(PRINTNAME(tmp))) == n) {
        tag = tmp;
        match = FULL;
        break;
        }
        else if (match == PARTIAL)
        /* this match is partial and we already have a partial match,
           so the query is ambiguous and we return R_NilValue */
        return R_NilValue;
        else {
        tag = tmp;
        match = PARTIAL;
        }
    }
    }

    /* unless a full match has been found, check for a "names" attribute */
    if (match != FULL && ! strncmp(CHAR(PRINTNAME(R_NamesSymbol)), str, n)) {
    if (strlen(CHAR(PRINTNAME(R_NamesSymbol))) == n) {
        /* we have a full match on "names" */
        tag = R_NamesSymbol;
        match = FULL;
    }
    else if (match == NONE) {
        /* no match on other attributes and a partial match on "names" */
        tag = R_NamesSymbol;
        match = PARTIAL;
    }
    else if (match == PARTIAL) {
        /* There is a partial match on "names" and on another
           attribute. If there really is a "names" attribute, then the
           query is ambiguous and we return R_NilValue.  If there is no
           "names" attribute, then the partially matched one, which is
           the current value of tag, can be used. */
        if (getAttrib(s, R_NamesSymbol) != R_NilValue)
        return R_NilValue;
    }
    }

    if (match == NONE)
    return R_NilValue;
    else 
    return getAttrib(s, tag);
}

SEXP do_attrgets(SEXP call, SEXP op, SEXP args, SEXP env)
{
    /*  attr(obj, "<name>")  <-  value  */
    SEXP obj, name, value;

    obj = eval(CAR(args), env);
    if (NAMED(obj) == 2)
    PROTECT(obj = duplicate(obj));
    else
    PROTECT(obj);

    PROTECT(name = eval(CADR(args), env));
    if (!isValidString(name))
    errorcall(call, "name must be non-null character");

    /* no eval(.), RHS is already evaluated: */
    /* now it's a promise so we should eval it -RG- */
    PROTECT(value = eval(CADDR(args), env));
    setAttrib(obj, name, value);
    UNPROTECT(3);
    return obj;
}


/* These provide useful shortcuts which give access to */
/* the dimnames for matrices and arrays in a standard form. */

void GetMatrixDimnames(SEXP x, SEXP *rl, SEXP *cl, char **rn, char **cn)
{
    SEXP dimnames = getAttrib(x, R_DimNamesSymbol);
    SEXP nn;

    if (isNull(dimnames)) {
    *rl = R_NilValue;
    *cl = R_NilValue;
    *rn = NULL;
    *cn = NULL;
    }
    else {
    *rl = VECTOR_ELT(dimnames, 0);
    *cl = VECTOR_ELT(dimnames, 1);
    nn = getAttrib(dimnames, R_NamesSymbol);
        if (isNull(nn)) {
        *rn = NULL;
        *cn = NULL;
        }
    else {
        *rn = CHAR(STRING_ELT(nn, 0));
        *cn = CHAR(STRING_ELT(nn, 1));
        }
    }
}


SEXP GetArrayDimnames(SEXP x)
{
    return getAttrib(x, R_DimNamesSymbol);
}