The R Project SVN R

/*

 *  R : A Computer Language for Statistical Data Analysis

 *  Copyright (C) 1995, 1996  Robert Gentleman and Ross Ihaka

 *  Copyright (C) 2002-3     The R Foundation

 *  Copyright (C) 1999-2013  The R 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, 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, a copy is available at

 *  http://www.r-project.org/Licenses/

 */

/*  This module contains support for S-style generic */

/*  functions and "class" support.  Gag, barf ...  */

#ifdef HAVE_CONFIG_H

#include <config.h>

#endif

#define R_USE_SIGNALS 1

#include <Defn.h>

#include <Internal.h>

#include <R_ext/RS.h> /* for Calloc, Realloc and for S4 object bit */

static SEXP GetObject(RCNTXT *cptr)

{

    SEXP s, sysp, b, formals, funcall, tag;

    sysp = R_GlobalContext->sysparent;

    PROTECT(funcall = R_syscall(0, cptr));

    if ( TYPEOF(CAR(funcall)) == SYMSXP )

	PROTECT(b = findFun(CAR(funcall), sysp));

    else

	PROTECT(b = eval(CAR(funcall), sysp));

    /**** use R_sysfunction here instead */

    if (TYPEOF(b) != CLOSXP) error(_("generic 'function' is not a function"));

    formals = FORMALS(b);

    tag = TAG(formals);

    if (tag != R_NilValue && tag != R_DotsSymbol) {

	s = NULL;

	/** exact matches **/

	for (b = cptr->promargs ; b != R_NilValue ; b = CDR(b))

	    if (TAG(b) != R_NilValue && pmatch(tag, TAG(b), 1)) {

		if (s != NULL)

		    error(_("formal argument \"%s\" matched by multiple actual arguments"), tag);

		else

		    s = CAR(b);

	    }

	if (s == NULL)

	    /** partial matches **/

	    for (b = cptr->promargs ; b != R_NilValue ; b = CDR(b))

		if (TAG(b) != R_NilValue && pmatch(tag, TAG(b), 0)) {

		    if ( s != NULL)

			error(_("formal argument \"%s\" matched by multiple actual arguments"), tag);

		    else

			s = CAR(b);

		}

	if (s == NULL)

	    /** first untagged argument **/

	    for (b = cptr->promargs ; b != R_NilValue ; b = CDR(b))

		if (TAG(b) == R_NilValue )

		{

		    s = CAR(b);

		    break;

		}

	if (s == NULL)

	    s = CAR(cptr->promargs);

/*

	    error("failed to match argument for dispatch");

*/

    }

    else

	s = CAR(cptr->promargs);

    UNPROTECT(2);

    if (TYPEOF(s) == PROMSXP) {

	if (PRVALUE(s) == R_UnboundValue)

	    s = eval(s, R_BaseEnv);

	else

	    s = PRVALUE(s);

    }

    return(s);

}

static SEXP applyMethod(SEXP call, SEXP op, SEXP args, SEXP rho, SEXP newrho)

{

    SEXP ans;

    if (TYPEOF(op) == SPECIALSXP) {

	int save = R_PPStackTop, flag = PRIMPRINT(op);

	const void *vmax = vmaxget();

	R_Visible = flag != 1;

	ans = PRIMFUN(op) (call, op, args, rho);

	if (flag < 2) R_Visible = flag != 1;

	check_stack_balance(op, save);

	vmaxset(vmax);

    }

    /* In other places we add a context to builtins when profiling,

       but we have not bothered here (as there seem to be no primitives

       used as methods, and this would have to be a primitive to be

       found).

     */

    else if (TYPEOF(op) == BUILTINSXP) {

	int save = R_PPStackTop, flag = PRIMPRINT(op);

	const void *vmax = vmaxget();

	PROTECT(args = evalList(args, rho, call, 0));

	R_Visible = flag != 1;

	ans = PRIMFUN(op) (call, op, args, rho);

	if (flag < 2) R_Visible = flag != 1;

	UNPROTECT(1);

	check_stack_balance(op, save);

	vmaxset(vmax);

    }

    else if (TYPEOF(op) == CLOSXP) {

	ans = applyClosure(call, op, args, rho, newrho);

    }

    else

	ans = R_NilValue;  /* for -Wall */

    return ans;

}

/* "newintoold" -  a destructive matching of arguments; */

/* newargs comes first; any element of oldargs with */

/* a name that matches a named newarg is deleted; the */

/* two resulting lists are appended and returned. */

/* S claims to do this (white book) but doesn't seem to. */

static SEXP newintoold(SEXP _new, SEXP old)

{

    if (_new == R_NilValue) return R_NilValue;

    SETCDR(_new, newintoold(CDR(_new),old));

    while (old != R_NilValue) {

	if (TAG(old) != R_NilValue && TAG(old) == TAG(_new)) {

	    SETCAR(old, CAR(_new));

	    return CDR(_new);

	}

	old = CDR(old);

    }

    return _new;

}

static SEXP matchmethargs(SEXP oldargs, SEXP newargs)

{

    newargs = newintoold(newargs, oldargs);

    return listAppend(oldargs, newargs);

}

#ifdef S3_for_S4_warn /* not currently used */

static SEXP s_check_S3_for_S4 = 0;

void R_warn_S3_for_S4(SEXP method) {

  SEXP call;

  if(!s_check_S3_for_S4)

    s_check_S3_for_S4 = install(".checkS3forS4");

  PROTECT(call = lang2(s_check_S3_for_S4, method));

  eval(call, R_MethodsNamespace);

  UNPROTECT(1);

}

#endif

/*  usemethod  -  calling functions need to evaluate the object

 *  (== 2nd argument).	They also need to ensure that the

 *  argument list is set up in the correct manner.

 *

 *    1. find the context for the calling function (i.e. the generic)

 *	 this gives us the unevaluated arguments for the original call

 *

 *    2. create an environment for evaluating the method and insert

 *	 a handful of variables (.Generic, .Class and .Method) into

 *	 that environment. Also copy any variables in the env of the

 *	 generic that are not formal (or actual) arguments.

 *

 *    3. fix up the argument list; it should be the arguments to the

 *	 generic matched to the formals of the method to be invoked */

attribute_hidden

SEXP R_LookupMethod(SEXP method, SEXP rho, SEXP callrho, SEXP defrho)

{

    SEXP val;

    if (TYPEOF(callrho) == NILSXP) {

	error(_("use of NULL environment is defunct"));

	callrho = R_BaseEnv;

    } else

	if (TYPEOF(callrho) != ENVSXP)

	    error(_("bad generic call environment"));

    if (TYPEOF(defrho) == NILSXP) {

	    error(_("use of NULL environment is defunct"));

	    defrho = R_BaseEnv;

    } else

	if (TYPEOF(defrho) != ENVSXP)

	    error(_("bad generic definition environment"));

    if (defrho == R_BaseEnv)

	defrho = R_BaseNamespace;

    /* This evaluates promises */

    val = findVar1(method, callrho, FUNSXP, TRUE);

    if (isFunction(val))

	return val;

    else {

	/* We assume here that no one registered a non-function */

	SEXP table = findVarInFrame3(defrho,

				     install(".__S3MethodsTable__."),

				     TRUE);

	if (TYPEOF(table) == PROMSXP) table = eval(table, R_BaseEnv);

	if (TYPEOF(table) == ENVSXP) {

	    val = findVarInFrame3(table, method, TRUE);

	    if (TYPEOF(val) == PROMSXP) val = eval(val, rho);

	    if (val != R_UnboundValue) return val;

	}

	return R_UnboundValue;

    }

}

#ifdef UNUSED

static int match_to_obj(SEXP arg, SEXP obj) {

  return (arg == obj) ||

    (TYPEOF(arg) == PROMSXP && PRVALUE(arg) == obj);

}

#endif

/* look up the class name in the methods package table of S3 classes

   which should be explicitly converted when an S3 method is applied

   to an object from an S4 subclass.

*/

int isBasicClass(const char *ss) {

    static SEXP s_S3table = 0;

    if(!s_S3table) {

      s_S3table = findVarInFrame3(R_MethodsNamespace, install(".S3MethodsClasses"), TRUE);

      if(s_S3table == R_UnboundValue)

	error(_("no '.S3MethodsClass' table, cannot use S4 objects with S3 methods ('methods' package not attached?)"));

	if (TYPEOF(s_S3table) == PROMSXP)  /* findVar... ignores lazy data */

	    s_S3table = eval(s_S3table, R_MethodsNamespace);

    }

    if(s_S3table == R_UnboundValue)

      return FALSE; /* too screwed up to do conversions */

    return findVarInFrame3(s_S3table, install(ss), FALSE) != R_UnboundValue;

}

attribute_hidden

int usemethod(const char *generic, SEXP obj, SEXP call, SEXP args,

	      SEXP rho, SEXP callrho, SEXP defrho, SEXP *ans)

{

    SEXP klass, method, sxp, t, s, matchedarg, sort_list;

    SEXP op, formals, newrho, newcall;

    char buf[512];

    int i, j, nclass, matched, /* S4toS3, */ nprotect;

    RCNTXT *cptr;

    /* Get the context which UseMethod was called from. */

    cptr = R_GlobalContext;

    if ( !(cptr->callflag & CTXT_FUNCTION) || cptr->cloenv != rho)

	error(_("'UseMethod' used in an inappropriate fashion"));

    /* Create a new environment without any */

    /* of the formals to the generic in it. */

    PROTECT(newrho = allocSExp(ENVSXP));

    op = CAR(cptr->call);

    switch (TYPEOF(op)) {

    case SYMSXP:

	PROTECT(op = findFun(op, cptr->sysparent));

	break;

    case LANGSXP:

	PROTECT(op = eval(op, cptr->sysparent));

	break;

    case CLOSXP:

    case BUILTINSXP:

    case SPECIALSXP:

	PROTECT(op);

	break;

    default:

	error(_("invalid generic function in 'usemethod'"));

    }

    nprotect = 5;

    if (TYPEOF(op) == CLOSXP) {

	formals = FORMALS(op);

	for (s = FRAME(cptr->cloenv); s != R_NilValue; s = CDR(s)) {

	    matched = 0;

	    for (t = formals; t != R_NilValue; t = CDR(t))

	        if (TAG(t) == TAG(s)) {

		    matched = 1;

		}

	    if (!matched) defineVar(TAG(s), CAR(s), newrho);

	}

    }

    PROTECT(matchedarg = cptr->promargs);

    PROTECT(newcall = duplicate(cptr->call));

    PROTECT(klass = R_data_class2(obj));

    sort_list = install("sort.list");

    nclass = length(klass);

    for (i = 0; i < nclass; i++) {

	const void *vmax = vmaxget();

        const char *ss = translateChar(STRING_ELT(klass, i));

	if(strlen(generic) + strlen(ss) + 2 > 512)

	    error(_("class name too long in '%s'"), generic);

	snprintf(buf, 512, "%s.%s", generic, ss);

	method = install(buf);

	vmaxset(vmax);

	sxp = R_LookupMethod(method, rho, callrho, defrho);

	if (isFunction(sxp)) {

	    if(method == sort_list && CLOENV(sxp) == R_BaseNamespace)

		continue; /* kludge because sort.list is not a method */

            if( RDEBUG(op) || RSTEP(op) )

                SET_RSTEP(sxp, 1);

	    defineVar(R_dot_Generic, mkString(generic), newrho);

	    if (i > 0) {

	        int ii;

		PROTECT(t = allocVector(STRSXP, nclass - i));

		for(j = 0, ii = i; j < length(t); j++, ii++)

		      SET_STRING_ELT(t, j, STRING_ELT(klass, ii));

		setAttrib(t, install("previous"), klass);

		defineVar(R_dot_Class, t, newrho);

		UNPROTECT(1);

	    } else

		defineVar(R_dot_Class, klass, newrho);

	    PROTECT(t = mkString(buf));

	    defineVar(R_dot_Method, t, newrho);

	    UNPROTECT(1);

	    defineVar(R_dot_GenericCallEnv, callrho, newrho);

	    defineVar(R_dot_GenericDefEnv, defrho, newrho);

	    t = newcall;

	    SETCAR(t, method);

	    R_GlobalContext->callflag = CTXT_GENERIC;

	    *ans = applyMethod(t, sxp, matchedarg, rho, newrho);

	    R_GlobalContext->callflag = CTXT_RETURN;

	    UNPROTECT(nprotect);

	    return 1;

	}

    }

    if(strlen(generic) + strlen("default") + 2 > 512)

	error(_("class name too long in '%s'"), generic);

    snprintf(buf, 512, "%s.default", generic);

    method = install(buf);

    sxp = R_LookupMethod(method, rho, callrho, defrho);

    if (isFunction(sxp)) {

        if( RDEBUG(op) || RSTEP(op) )

            SET_RSTEP(sxp, 1);

	defineVar(R_dot_Generic, mkString(generic), newrho);

	defineVar(R_dot_Class, R_NilValue, newrho);

	PROTECT(t = mkString(buf));

	defineVar(R_dot_Method, t, newrho);

	UNPROTECT(1);

	defineVar(R_dot_GenericCallEnv, callrho, newrho);

	defineVar(R_dot_GenericDefEnv, defrho, newrho);

	t = newcall;

	SETCAR(t, method);

	R_GlobalContext->callflag = CTXT_GENERIC;

	*ans = applyMethod(t, sxp, matchedarg, rho, newrho);

	R_GlobalContext->callflag = CTXT_RETURN;

	UNPROTECT(5);

	return 1;

    }

    UNPROTECT(5);

    cptr->callflag = CTXT_RETURN;

    return 0;

}

/* Note: "do_usemethod" is not the only entry point to

   "usemethod". Things like [ and [[ call usemethod directly,

   hence do_usemethod should just be an interface to usemethod.

*/

/* This is a primitive SPECIALSXP */

SEXP attribute_hidden do_usemethod(SEXP call, SEXP op, SEXP args, SEXP env)

{

    SEXP ans, generic = R_NilValue /* -Wall */, obj, val;

    SEXP callenv, defenv;

    SEXP ap, argList;

    RCNTXT *cptr;

    PROTECT(ap = list2(R_NilValue, R_NilValue));

    SET_TAG(ap,  install("generic"));

    SET_TAG(CDR(ap), install("object"));

    PROTECT(argList =  matchArgs(ap, args, call));

    if (CAR(argList) == R_MissingArg)

	errorcall(call, _("there must be a 'generic' argument"));

    else

	PROTECT(generic = eval(CAR(argList), env));

    if(!isString(generic) || length(generic) != 1)

	errorcall(call, _("'generic' argument must be a character string"));

    /* get environments needed for dispatching.

       callenv = environment from which the generic was called

       defenv = environment where the generic was defined */

    cptr = R_GlobalContext;

    if ( !(cptr->callflag & CTXT_FUNCTION) || cptr->cloenv != env)

	errorcall(call, _("'UseMethod' used in an inappropriate fashion"));

    callenv = cptr->sysparent;

    /* We need to find the generic to find out where it is defined.

       This is set up to avoid getting caught by things like

	mycoef <- function(x)

       {

	   mycoef <- function(x) stop("not this one")

	   UseMethod("mycoef")

       }

	The generic need not be a closure (Henrik Bengtsson writes

	UseMethod("$"), although only functions are documented.)

    */

    val = findVar1(installTrChar(STRING_ELT(generic, 0)),

		   ENCLOS(env), FUNSXP, TRUE); /* That has evaluated promises */

    if(TYPEOF(val) == CLOSXP) defenv = CLOENV(val);

    else defenv = R_BaseNamespace;

    if (CADR(argList) != R_MissingArg)

	PROTECT(obj = eval(CADR(argList), env));

    else {

	cptr = R_GlobalContext;

	while (cptr != NULL) {

	    if ( (cptr->callflag & CTXT_FUNCTION) && cptr->cloenv == env)

		break;

	    cptr = cptr->nextcontext;

	}

	if (cptr == NULL)

	    errorcall(call, _("'UseMethod' called from outside a function"));

	PROTECT(obj = GetObject(cptr));

    }

    if (TYPEOF(generic) != STRSXP ||

	LENGTH(generic) < 1 ||

	CHAR(STRING_ELT(generic, 0))[0] == '\0')

	errorcall(call, _("first argument must be a generic name"));

    if (usemethod(translateChar(STRING_ELT(generic, 0)), obj, call, CDR(args),

		  env, callenv, defenv, &ans) == 1) {

	UNPROTECT(3); /* obj, ap, argList */

	PROTECT(ans);

	findcontext(CTXT_RETURN, env, ans); /* does not return */

    }

    else {

	SEXP klass;

	int nclass;

	char cl[1000];

	PROTECT(klass = R_data_class2(obj));

	nclass = length(klass);

	if (nclass == 1)

	    strcpy(cl, translateChar(STRING_ELT(klass, 0)));

	else {

	    int i;

	    strcpy(cl, "c('");

	    for (i = 0; i < nclass; i++) {

		if (i > 0) strcat(cl, "', '");

		strcat(cl, translateChar(STRING_ELT(klass, i)));

	    }

	    strcat(cl, "')");

	}

	errorcall(call, _("no applicable method for '%s' applied to an object of class \"%s\""),

		  translateChar(STRING_ELT(generic, 0)), cl);

    }

    /* Not reached */

    return R_NilValue;

}

/*

   fixcall: fixes up the call when arguments to the function may

   have changed; for now we only worry about tagged args, appending

   them if they are not already there

*/

static SEXP fixcall(SEXP call, SEXP args)

{

    SEXP s, t;

    int found;

    for(t = args; t != R_NilValue; t = CDR(t)) {

	if(TAG(t) != R_NilValue) {

		found = 0;

		for(s = call; CDR(s) != R_NilValue; s = CDR(s))

		    if(TAG(CDR(s)) == TAG(t)) found = 1;

		if( !found ) {

			SETCDR(s, allocList(1));

			SET_TAG(CDR(s), TAG(t));

			SETCAR(CDR(s), duplicate(CAR(t)));

		}

	}

    }

    return call;

}

/* If NextMethod has any arguments the first must be the generic */

/* the second the object and any remaining are matched with the */

/* formals of the chosen method. */

#define ARGUSED(x) LEVELS(x)

/* This is a special .Internal */

SEXP attribute_hidden do_nextmethod(SEXP call, SEXP op, SEXP args, SEXP env)

{

    char buf[512], b[512], bb[512], tbuf[10];

    const char *sb, *sg, *sk;

    SEXP ans, s, t, klass, method, matchedarg, generic, nextfun;

    SEXP sysp, m, formals, actuals, tmp, newcall;

    SEXP a, group, basename;

    SEXP callenv, defenv;

    RCNTXT *cptr;

    int i, j;

    cptr = R_GlobalContext;

    cptr->callflag = CTXT_GENERIC;

    /* get the env NextMethod was called from */

    sysp = R_GlobalContext->sysparent;

    while (cptr != NULL) {

	if (cptr->callflag & CTXT_FUNCTION && cptr->cloenv == sysp) break;

	cptr = cptr->nextcontext;

    }

    if (cptr == NULL)

	error(_("'NextMethod' called from outside a function"));

    PROTECT(newcall = duplicate(cptr->call));

    /* eg get("print.ts")(1) */

    if (TYPEOF(CAR(cptr->call)) == LANGSXP)

       error(_("'NextMethod' called from an anonymous function"));

    /* Find dispatching environments. Promises shouldn't occur, but

       check to be on the safe side.  If the variables are not in the

       environment (the method was called outside a method dispatch)

       then chose reasonable defaults. */

    callenv = findVarInFrame3(R_GlobalContext->sysparent,

			      R_dot_GenericCallEnv, TRUE);

    if (TYPEOF(callenv) == PROMSXP)

	callenv = eval(callenv, R_BaseEnv);

    else if (callenv == R_UnboundValue)

	    callenv = env;

    defenv = findVarInFrame3(R_GlobalContext->sysparent,

			     R_dot_GenericDefEnv, TRUE);

    if (TYPEOF(defenv) == PROMSXP) defenv = eval(defenv, R_BaseEnv);

    else if (defenv == R_UnboundValue) defenv = R_GlobalEnv;

    /* set up the arglist */

    if (TYPEOF(CAR(cptr->call)) == CLOSXP)

	// e.g., in do.call(function(x) NextMethod('foo'),list())

	s = CAR(cptr->call);

    else

	s = R_LookupMethod(CAR(cptr->call), env, callenv, defenv);

    if (TYPEOF(s) == SYMSXP && s == R_UnboundValue)

	error(_("no calling generic was found: was a method called directly?"));

    if (TYPEOF(s) != CLOSXP){ /* R_LookupMethod looked for a function */

	errorcall(R_NilValue,

		  _("'function' is not a function, but of type %d"),

		  TYPEOF(s));

    }

    /* get formals and actuals; attach the names of the formals to

       the actuals, expanding any ... that occurs */

    formals = FORMALS(s);

    PROTECT(actuals = matchArgs(formals, cptr->promargs, call));

    i = 0;

    for(s = formals, t = actuals; s != R_NilValue; s = CDR(s), t = CDR(t)) {

	SET_TAG(t, TAG(s));

	if(TAG(t) == R_DotsSymbol) i = length(CAR(t));

    }

    if(i) {   /* we need to expand out the dots */

	PROTECT(t = allocList(i+length(actuals)-1));

	for(s = actuals, m = t; s != R_NilValue; s = CDR(s)) {

	    if(TYPEOF(CAR(s)) == DOTSXP) {

		for(i = 1, a = CAR(s); a != R_NilValue;

		    a = CDR(a), i++, m = CDR(m)) {

		    snprintf(tbuf, 10, "..%d", i);

		    SET_TAG(m, mkSYMSXP(mkChar(tbuf), R_UnboundValue));

		    SETCAR(m, CAR(a));

		}

	    } else {

		SET_TAG(m, TAG(s));

		SETCAR(m, CAR(s));

		m = CDR(m);

	    }

	}

	UNPROTECT(1);

	actuals = t;

    }

    PROTECT(actuals);

    /* we can't duplicate because it would force the promises */

    /* so we do our own duplication of the promargs */

    PROTECT(matchedarg = allocList(length(cptr->promargs)));

    for (t = matchedarg, s = cptr->promargs; t != R_NilValue;

	 s = CDR(s), t = CDR(t)) {

	SETCAR(t, CAR(s));

	SET_TAG(t, TAG(s));

    }

    for (t = matchedarg; t != R_NilValue; t = CDR(t)) {

	for (m = actuals; m != R_NilValue; m = CDR(m))

	    if (CAR(m) == CAR(t))  {

		if (CAR(m) == R_MissingArg) {

		    tmp = findVarInFrame3(cptr->cloenv, TAG(m), TRUE);

		    if (tmp == R_MissingArg) break;

		}

		SETCAR(t, mkPROMISE(TAG(m), cptr->cloenv));

		break;

	   }

    }

    /*

      Now see if there were any other arguments passed in

      Currently we seem to only allow named args to change

      or to be added, this is at variance with p. 470 of the

      White Book

    */

    s = CADDR(args); /* this is ... and we need to see if it's bound */

    if (s == R_DotsSymbol) {

	t = findVarInFrame3(env, s, TRUE);

	if (t != R_NilValue && t != R_MissingArg) {

	    SET_TYPEOF(t, LISTSXP); /* a safe mutation */

	    s = matchmethargs(matchedarg, t);

	    UNPROTECT(1);

	    PROTECT(matchedarg = s);

	    newcall = fixcall(newcall, matchedarg);

	}

    }

    else

	error(_("wrong argument ..."));

    /*

      .Class is used to determine the next method; if it doesn't

      exist the first argument to the current method is used

      the second argument to NextMethod is another option but

      isn't currently used).

    */

    klass = findVarInFrame3(R_GlobalContext->sysparent,

			    R_dot_Class, TRUE);

    if (klass == R_UnboundValue) {

	s = GetObject(cptr);

	if (!isObject(s)) error(_("object not specified"));

	klass = getAttrib(s, R_ClassSymbol);

    }

    /* the generic comes from either the sysparent or it's named */

    generic = findVarInFrame3(R_GlobalContext->sysparent,

			      R_dot_Generic, TRUE);

    if (generic == R_UnboundValue)

	generic = eval(CAR(args), env);

    if( generic == R_NilValue )

	error(_("generic function not specified"));

    PROTECT(generic);

    if (!isString(generic) || length(generic) != 1)

	error(_("invalid generic argument to 'NextMethod'"));

    if (CHAR(STRING_ELT(generic, 0))[0] == '\0')

	error(_("generic function not specified"));

    /* determine whether we are in a Group dispatch */

    group = findVarInFrame3(R_GlobalContext->sysparent,

			    R_dot_Group, TRUE);

    if (group == R_UnboundValue) PROTECT(group = mkString(""));

    else PROTECT(group);

    if (!isString(group) || length(group) != 1)

	error(_("invalid 'group' argument found in 'NextMethod'"));

    /* determine the root: either the group or the generic will be it */

    if (CHAR(STRING_ELT(group, 0))[0] == '\0') basename = generic;

    else basename = group;

    nextfun = R_NilValue;

    /*

       Find the method currently being invoked and jump over the current call

       If t is R_UnboundValue then we called the current method directly

    */

    method = findVarInFrame3(R_GlobalContext->sysparent,

			     R_dot_Method, TRUE);

    if( method != R_UnboundValue) {

	const char *ss;

	if( !isString(method) )

	    error(_("wrong value for .Method"));

	for(i = 0; i < length(method); i++) {

	    ss = translateChar(STRING_ELT(method, i));

	    if(strlen(ss) >= 512)

		error(_("method name too long in '%s'"), ss);

	    snprintf(b, 512, "%s", ss);

	    if(strlen(b)) break;

	}

	/* for binary operators check that the second argument's method

	   is the same or absent */

	for(j = i; j < length(method); j++) {

	    const char *ss = translateChar(STRING_ELT(method, j));

	    if(strlen(ss) >= 512)

		error(_("method name too long in '%s'"), ss);

	    snprintf(bb, 512, "%s", ss);

	    if (strlen(bb) && strcmp(b,bb))

		warning(_("Incompatible methods ignored"));

	}

    }

    else {

	if(strlen(CHAR(PRINTNAME(CAR(cptr->call)))) >= 512)

	   error(_("call name too long in '%s'"),

		 EncodeChar(PRINTNAME(CAR(cptr->call))));

	snprintf(b, 512, "%s", CHAR(PRINTNAME(CAR(cptr->call))));

    }

    sb = translateChar(STRING_ELT(basename, 0));

    for (j = 0; j < length(klass); j++) {

	sk = translateChar(STRING_ELT(klass, j));

	if(strlen(sb) + strlen(sk) + 2 > 512)

	    error(_("class name too long in '%s'"), sb);

	snprintf(buf, 512, "%s.%s", sb, sk);

	if (!strcmp(buf, b)) break;

    }

    if (!strcmp(buf, b)) /* we found a match and start from there */

      j++;

    else

      j = 0;  /*no match so start with the first element of .Class */

    /* we need the value of i on exit from the for loop to figure out

	   how many classes to drop. */

    sg = translateChar(STRING_ELT(generic, 0));

    for (i = j ; i < length(klass); i++) {

	sk = translateChar(STRING_ELT(klass, i));

	if(strlen(sg) + strlen(sk) + 2 > 512)

	    error(_("class name too long in '%s'"), sg);

	snprintf(buf, 512, "%s.%s", sg, sk);

	nextfun = R_LookupMethod(install(buf), env, callenv, defenv);

	if (isFunction(nextfun)) break;

	if (group != R_UnboundValue) {

	    /* if not Generic.foo, look for Group.foo */

	    if(strlen(sb) + strlen(sk) + 2 > 512)

		error(_("class name too long in '%s'"), sb);

	    snprintf(buf, 512, "%s.%s", sb, sk);

	    nextfun = R_LookupMethod(install(buf), env, callenv, defenv);

	    if(isFunction(nextfun))

		break;

	}

	if (isFunction(nextfun))

	    break;

    }

    if (!isFunction(nextfun)) {

	snprintf(buf, 512, "%s.default", sg);

	nextfun = R_LookupMethod(install(buf), env, callenv, defenv);

	/* If there is no default method, try the generic itself,

	   provided it is primitive or a wrapper for a .Internal

	   function of the same name.

	 */

	if (!isFunction(nextfun)) {

	    t = install(sg);

	    nextfun = findVar(t, env);

	    if (TYPEOF(nextfun) == PROMSXP)

		nextfun = eval(nextfun, env);

	    if (!isFunction(nextfun))

		error(_("no method to invoke"));

	    if (TYPEOF(nextfun) == CLOSXP) {

		if (INTERNAL(t) != R_NilValue)

		    nextfun = INTERNAL(t);

		else

		    error(_("no method to invoke"));

	    }

	}

    }

    PROTECT(s = allocVector(STRSXP, length(klass) - i));

    PROTECT(klass = duplicate(klass));

    PROTECT(m = allocSExp(ENVSXP));

    for (j = 0; j < length(s); j++)

	SET_STRING_ELT(s, j, duplicate(STRING_ELT(klass, i++)));

    setAttrib(s, install("previous"), klass);

    defineVar(R_dot_Class, s, m);

    /* It is possible that if a method was called directly that

	'method' is unset */

    if (method != R_UnboundValue) {

	/* for Ops we need `method' to be a vector */

	PROTECT(method = duplicate(method));

	for(j = 0; j < length(method); j++) {

	    if (strlen(CHAR(STRING_ELT(method,j))))

		SET_STRING_ELT(method, j,  mkChar(buf));

	}

    } else

	PROTECT(method = mkString(buf));

    defineVar(R_dot_Method, method, m);

    defineVar(R_dot_GenericCallEnv, callenv, m);

    defineVar(R_dot_GenericDefEnv, defenv, m);

    method = install(buf);

    defineVar(R_dot_Generic, generic, m);

    defineVar(R_dot_Group, group, m);

    SETCAR(newcall, method);

    /* applyMethod expects that the parent of the caller is the caller

       of the generic, so fixup by brute force. This should fix

       PR#15267 --pd */

    R_GlobalContext->sysparent = callenv;

    ans = applyMethod(newcall, nextfun, matchedarg, env, m);

    UNPROTECT(10);

    return(ans);

}

/* primitive */

SEXP attribute_hidden do_unclass(SEXP call, SEXP op, SEXP args, SEXP env)

{

    checkArity(op, args);

    check1arg(args, call, "x");

    switch(TYPEOF(CAR(args))) {

    case ENVSXP:

	errorcall(call, _("cannot unclass an environment"));

	break;

    case EXTPTRSXP:

	errorcall(call, _("cannot unclass an external pointer"));

	break;

    default:

	break;

    }

    if (isObject(CAR(args))) {

	SETCAR(args, duplicate(CAR(args)));

	setAttrib(CAR(args), R_ClassSymbol, R_NilValue);

    }

    return CAR(args);

}

/* NOTE: Fast  inherits(x, what)    in ../include/Rinlinedfuns.h

 * ----        ----------------- */

/** C API for  R  inherits(x, what, which)

 *

 * @param x any R object

 * @param what character vector

 * @param which logical: "want vector result" ?

 *

 * @return if which is false, logical TRUE or FALSE

 *	   if which is true, integer vector of length(what) ..

 */

static SEXP inherits3(SEXP x, SEXP what, SEXP which)

{

    const void *vmax = vmaxget();

    SEXP klass, rval = R_NilValue /* -Wall */;

    if(IS_S4_OBJECT(x))

	PROTECT(klass = R_data_class2(x));

    else

	PROTECT(klass = R_data_class(x, FALSE));

    int nclass = length(klass);

    if(!isString(what))

	error(_("'what' must be a character vector"));

    int j, nwhat = length(what);

    if( !isLogical(which) || (length(which) != 1) )

	error(_("'which' must be a length 1 logical vector"));

    int isvec = asLogical(which);

#ifdef _be_too_picky_

    if(IS_S4_OBJECT(x) && nwhat == 1 && !isvec &&

       !isNull(R_getClassDef(translateChar(STRING_ELT(what, 0)))))

	warning(_("use 'is()' instead of 'inherits()' on S4 objects"));

#endif

    if(isvec)

	PROTECT(rval = allocVector(INTSXP, nwhat));

    for(j = 0; j < nwhat; j++) {

	const char *ss = translateChar(STRING_ELT(what, j)); int i;

	if(isvec)

	    INTEGER(rval)[j] = 0;

	for(i = 0; i < nclass; i++) {

	    if(!strcmp(translateChar(STRING_ELT(klass, i)), ss)) {

		if(isvec)

		    INTEGER(rval)[j] = i+1;

		else {

		    UNPROTECT(1);

		    return mkTrue();

		}

		break;

	    }

	}

    }

    vmaxset(vmax);

    if(!isvec) {

    	UNPROTECT(1);

	return mkFalse();

    }

    UNPROTECT(2);

    return rval;

}

SEXP attribute_hidden do_inherits(SEXP call, SEXP op, SEXP args, SEXP env)

{

    checkArity(op, args);

    return inherits3(/* x = */ CAR(args),

		     /* what = */ CADR(args),

		     /* which = */ CADDR(args));

}

/**

 * Return the 0-based index of an is() match in a vector of class-name

 * strings terminated by an empty string.  Returns -1 for no match.

 *

 * @param x  an R object, about which we want is(x, .) information.

 * @param valid vector of possible matches terminated by an empty string.

 * @param rho  the environment in which the class definitions exist.

 *

 * @return index of match or -1 for no match

 */

int R_check_class_and_super(SEXP x, const char **valid, SEXP rho)

{