/*
 *  R : A Computer Language for Statistical Data Analysis
 *  Copyright (C) 1995, 1996  Robert Gentleman and Ross Ihaka
 *  Copyright (C) 1998-2019   The R Core Team
 *  Copyright (C) 2002-2005  The R Foundation
 *
 *  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, a copy is available at
 *  https://www.R-project.org/Licenses/
 */

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

#include <math.h> /* avoid redefinition of extern in Defn.h */
#include <float.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>

#define __MAIN__
#define R_USE_SIGNALS 1
#include "Defn.h"
#include <Internal.h>
#include "Rinterface.h"
#include "IOStuff.h"
#include "Fileio.h"
#include "Parse.h"
#include "Startup.h"

#include <locale.h>
#include <R_ext/Print.h>

#ifdef ENABLE_NLS
void attribute_hidden nl_Rdummy(void)
{
    /* force this in as packages use it */
    dgettext("R", "dummy - do not translate");
}
#endif


/* The 'real' main() program is in Rmain.c on Unix-alikes, and
   src/gnuwin/front-ends/graphappmain.c on Windows, unless of course
   R is embedded */

/* Global Variables:  For convenience, all interpeter global symbols
 * ================   are declared in Defn.h as extern -- and defined here.
 *
 * NOTE: This is done by using some preprocessor trickery.  If __MAIN__
 * is defined as above, there is a sneaky
 *     #define extern
 * so that the same code produces both declarations and definitions.
 *
 * This does not include user interface symbols which are included
 * in separate platform dependent modules.
 */

void Rf_callToplevelHandlers(SEXP expr, SEXP value, Rboolean succeeded,
			     Rboolean visible);

static int ParseBrowser(SEXP, SEXP);


	/* Read-Eval-Print Loop [ =: REPL = repl ] with input from a file */

static void R_ReplFile(FILE *fp, SEXP rho)
{
    ParseStatus status;
    int count=0;
    int savestack;
    RCNTXT cntxt;

    R_InitSrcRefState(&cntxt);
    savestack = R_PPStackTop;
    for(;;) {
	R_PPStackTop = savestack;
	R_CurrentExpr = R_Parse1File(fp, 1, &status);
	switch (status) {
	case PARSE_NULL:
	    break;
	case PARSE_OK:
	    R_Visible = FALSE;
	    R_EvalDepth = 0;
	    resetTimeLimits();
	    count++;
	    PROTECT(R_CurrentExpr);
	    R_CurrentExpr = eval(R_CurrentExpr, rho);
	    SET_SYMVALUE(R_LastvalueSymbol, R_CurrentExpr);
	    UNPROTECT(1);
	    if (R_Visible)
		PrintValueEnv(R_CurrentExpr, rho);
	    if( R_CollectWarnings )
		PrintWarnings();
	    break;
	case PARSE_ERROR:
	    R_FinalizeSrcRefState();
	    parseError(R_NilValue, R_ParseError);
	    break;
	case PARSE_EOF:
	    endcontext(&cntxt);
	    R_FinalizeSrcRefState();
	    return;
	    break;
	case PARSE_INCOMPLETE:
	    /* can't happen: just here to quieten -Wall */
	    break;
	}
    }
}

/* Read-Eval-Print loop with interactive input */
static int prompt_type;
static char BrowsePrompt[20];

static const char *R_PromptString(int browselevel, int type)
{
    if (R_Slave) {
	BrowsePrompt[0] = '\0';
	return BrowsePrompt;
    }
    else {
	if(type == 1) {
	    if(browselevel) {
		snprintf(BrowsePrompt, 20, "Browse[%d]> ", browselevel);
		return BrowsePrompt;
	    }
	    return CHAR(STRING_ELT(GetOption1(install("prompt")), 0));
	}
	else {
	    return CHAR(STRING_ELT(GetOption1(install("continue")), 0));
	}
    }
}

/*
  This is a reorganization of the REPL (Read-Eval-Print Loop) to separate
  the loop from the actions of the body. The motivation is to make the iteration
  code (Rf_ReplIteration) available as a separately callable routine
  to avoid cutting and pasting it when one wants a single iteration
  of the loop. This is needed as we allow different implementations
  of event loops. Currently (summer 2002), we have a package in
  preparation that uses Rf_ReplIteration within either the
  Tcl or Gtk event loop and allows either (or both) loops to
  be used as a replacement for R's loop and take over the event
  handling for the R process.

  The modifications here are intended to leave the semantics of the REPL
  unchanged, just separate into routines. So the variables that maintain
  the state across iterations of the loop are organized into a structure
  and passed to Rf_ReplIteration() from Rf_ReplConsole().
*/


/**
  (local) Structure for maintaining and exchanging the state between
  Rf_ReplConsole and its worker routine Rf_ReplIteration which is the
  implementation of the body of the REPL.

  In the future, we may need to make this accessible to packages
  and so put it into one of the public R header files.
 */
typedef struct {
  ParseStatus    status;
  int            prompt_type;
  int            browselevel;
  unsigned char  buf[CONSOLE_BUFFER_SIZE+1];
  unsigned char *bufp;
} R_ReplState;


/**
  This is the body of the REPL.
  It attempts to parse the first line or expression of its input,
  and optionally request input from the user if none is available.
  If the input can be parsed correctly,
     i) the resulting expression is evaluated,
    ii) the result assigned to .Last.Value,
   iii) top-level task handlers are invoked.

 If the input cannot be parsed, i.e. there is a syntax error,
 it is incomplete, or we encounter an end-of-file, then we
 change the prompt accordingly.

 The "cursor" for the input buffer is moved to the next starting
 point, i.e. the end of the first line or after the first ;.
 */
int
Rf_ReplIteration(SEXP rho, int savestack, int browselevel, R_ReplState *state)
{
    int c, browsevalue;
    SEXP value, thisExpr;
    Rboolean wasDisplayed = FALSE;

    if(!*state->bufp) {
	    R_Busy(0);
	    if (R_ReadConsole(R_PromptString(browselevel, state->prompt_type),
			      state->buf, CONSOLE_BUFFER_SIZE, 1) == 0)
		return(-1);
	    state->bufp = state->buf;
    }
#ifdef SHELL_ESCAPE /* not default */
    if (*state->bufp == '!') {
	    R_system(&(state->buf[1]));
	    state->buf[0] = '\0';
	    return(0);
    }
#endif /* SHELL_ESCAPE */
    while((c = *state->bufp++)) {
	    R_IoBufferPutc(c, &R_ConsoleIob);
	    if(c == ';' || c == '\n') break;
    }

    R_PPStackTop = savestack;
    R_CurrentExpr = R_Parse1Buffer(&R_ConsoleIob, 0, &state->status);

    switch(state->status) {

    case PARSE_NULL:

	/* The intention here is to break on CR but not on other
	   null statements: see PR#9063 */
	if (browselevel && !R_DisableNLinBrowser
	    && !strcmp((char *) state->buf, "\n")) return -1;
	R_IoBufferWriteReset(&R_ConsoleIob);
	state->prompt_type = 1;
	return 1;

    case PARSE_OK:

	R_IoBufferReadReset(&R_ConsoleIob);
	R_CurrentExpr = R_Parse1Buffer(&R_ConsoleIob, 1, &state->status);
	if (browselevel) {
	    browsevalue = ParseBrowser(R_CurrentExpr, rho);
	    if(browsevalue == 1) return -1;
	    if(browsevalue == 2) {
		R_IoBufferWriteReset(&R_ConsoleIob);
		return 0;
	    }
	    /* PR#15770 We don't want to step into expressions entered at the debug prompt.
	       The 'S' will be changed back to 's' after the next eval. */
	    if (R_BrowserLastCommand == 's') R_BrowserLastCommand = 'S';
	}
	R_Visible = FALSE;
	R_EvalDepth = 0;
	resetTimeLimits();
	PROTECT(thisExpr = R_CurrentExpr);
	R_Busy(1);
	PROTECT(value = eval(thisExpr, rho));
	SET_SYMVALUE(R_LastvalueSymbol, value);
	wasDisplayed = R_Visible;
	if (R_Visible)
	    PrintValueEnv(value, rho);
	if (R_CollectWarnings)
	    PrintWarnings();
	Rf_callToplevelHandlers(thisExpr, value, TRUE, wasDisplayed);
	R_CurrentExpr = value; /* Necessary? Doubt it. */
	UNPROTECT(2); /* thisExpr, value */
	if (R_BrowserLastCommand == 'S') R_BrowserLastCommand = 's';
	R_IoBufferWriteReset(&R_ConsoleIob);
	state->prompt_type = 1;
	return(1);

    case PARSE_ERROR:

	state->prompt_type = 1;
	parseError(R_NilValue, 0);
	R_IoBufferWriteReset(&R_ConsoleIob);
	return(1);

    case PARSE_INCOMPLETE:

	R_IoBufferReadReset(&R_ConsoleIob);
	state->prompt_type = 2;
	return(2);

    case PARSE_EOF:

	return(-1);
	break;
    }

    return(0);
}

static void R_ReplConsole(SEXP rho, int savestack, int browselevel)
{
    int status;
    R_ReplState state = { PARSE_NULL, 1, 0, "", NULL};

    R_IoBufferWriteReset(&R_ConsoleIob);
    state.buf[0] = '\0';
    state.buf[CONSOLE_BUFFER_SIZE] = '\0';
    /* stopgap measure if line > CONSOLE_BUFFER_SIZE chars */
    state.bufp = state.buf;
    if(R_Verbose)
	REprintf(" >R_ReplConsole(): before \"for(;;)\" {main.c}\n");
    for(;;) {
	status = Rf_ReplIteration(rho, savestack, browselevel, &state);
	if(status < 0) {
	  if (state.status == PARSE_INCOMPLETE)
	    error(_("unexpected end of input"));
	  return;
	}
    }
}


static unsigned char DLLbuf[CONSOLE_BUFFER_SIZE+1], *DLLbufp;

static void check_session_exit()
{
    if (! R_Interactive) {
	/* This funtion will be called again after a LONGJMP if an
	   error is signaled from one of the functions called. The
	   'exiting' variable identifies this and results in
	   R_Suicide. */
	static Rboolean exiting = FALSE;
	if (exiting)
	    R_Suicide(_("error during cleanup\n"));
	else {
	    exiting = TRUE;
	    if (GetOption1(install("error")) != R_NilValue) {
		exiting = FALSE;
		return;
	    }
	    REprintf(_("Execution halted\n"));
	    R_CleanUp(SA_NOSAVE, 1, 0); /* quit, no save, no .Last, status=1 */
	}
	
    }
}

void R_ReplDLLinit(void)
{
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    R_IoBufferWriteReset(&R_ConsoleIob);
    prompt_type = 1;
    DLLbuf[0] = DLLbuf[CONSOLE_BUFFER_SIZE] = '\0';
    DLLbufp = DLLbuf;
}

/* FIXME: this should be re-written to use Rf_ReplIteration
   since it gets out of sync with it over time */
int R_ReplDLLdo1(void)
{
    int c;
    ParseStatus status;
    SEXP rho = R_GlobalEnv, lastExpr;
    Rboolean wasDisplayed = FALSE;

    if(!*DLLbufp) {
	R_Busy(0);
	if (R_ReadConsole(R_PromptString(0, prompt_type), DLLbuf,
			  CONSOLE_BUFFER_SIZE, 1) == 0)
	    return -1;
	DLLbufp = DLLbuf;
    }
    while((c = *DLLbufp++)) {
	R_IoBufferPutc(c, &R_ConsoleIob);
	if(c == ';' || c == '\n') break;
    }
    R_PPStackTop = 0;
    R_CurrentExpr = R_Parse1Buffer(&R_ConsoleIob, 0, &status);

    switch(status) {
    case PARSE_NULL:
	R_IoBufferWriteReset(&R_ConsoleIob);
	prompt_type = 1;
	break;
    case PARSE_OK:
	R_IoBufferReadReset(&R_ConsoleIob);
	R_CurrentExpr = R_Parse1Buffer(&R_ConsoleIob, 1, &status);
	R_Visible = FALSE;
	R_EvalDepth = 0;
	resetTimeLimits();
	PROTECT(R_CurrentExpr);
	R_Busy(1);
	lastExpr = R_CurrentExpr;
	R_CurrentExpr = eval(R_CurrentExpr, rho);
	SET_SYMVALUE(R_LastvalueSymbol, R_CurrentExpr);
	wasDisplayed = R_Visible;
	if (R_Visible)
	    PrintValueEnv(R_CurrentExpr, rho);
	if (R_CollectWarnings)
	    PrintWarnings();
	Rf_callToplevelHandlers(lastExpr, R_CurrentExpr, TRUE, wasDisplayed);
	UNPROTECT(1);
	R_IoBufferWriteReset(&R_ConsoleIob);
	R_Busy(0);
	prompt_type = 1;
	break;
    case PARSE_ERROR:
	parseError(R_NilValue, 0);
	R_IoBufferWriteReset(&R_ConsoleIob);
	prompt_type = 1;
	break;
    case PARSE_INCOMPLETE:
	R_IoBufferReadReset(&R_ConsoleIob);
	prompt_type = 2;
	break;
    case PARSE_EOF:
	return -1;
	break;
    }
    return prompt_type;
}

/* Main Loop: It is assumed that at this point that operating system */
/* specific tasks (dialog window creation etc) have been performed. */
/* We can now print a greeting, run the .First function and then enter */
/* the read-eval-print loop. */

static RETSIGTYPE handleInterrupt(int dummy)
{
    R_interrupts_pending = 1;
    signal(SIGINT, handleInterrupt);
}

/* this flag is set if R internal code is using send() and does not
   want to trigger an error on SIGPIPE (e.g., the httpd code).
   [It is safer and more portable than other methods of handling
   broken pipes on send().]
 */

#ifndef Win32
// controlled by the internal http server in the internet module
int R_ignore_SIGPIPE = 0;

static RETSIGTYPE handlePipe(int dummy)
{
    signal(SIGPIPE, handlePipe);
    if (!R_ignore_SIGPIPE) error("ignoring SIGPIPE signal");
}
#endif


#ifdef Win32
static int num_caught = 0;

static void win32_segv(int signum)
{
    /* NB: stack overflow is not an access violation on Win32 */
    {   /* A simple customized print of the traceback */
	SEXP trace, p, q;
	int line = 1, i;
	PROTECT(trace = R_GetTraceback(0));
	if(trace != R_NilValue) {
	    REprintf("\nTraceback:\n");
	    for(p = trace; p != R_NilValue; p = CDR(p), line++) {
		q = CAR(p); /* a character vector */
		REprintf("%2d: ", line);
		for(i = 0; i < LENGTH(q); i++)
		    REprintf("%s", CHAR(STRING_ELT(q, i)));
		REprintf("\n");
	    }
	    UNPROTECT(1);
	}
    }
    num_caught++;
    if(num_caught < 10) signal(signum, win32_segv);
    if(signum == SIGILL)
	error("caught access violation - continue with care");
    else
	error("caught access violation - continue with care");
}
#endif

#if defined(HAVE_SIGALTSTACK) && defined(HAVE_SIGACTION) && defined(HAVE_WORKING_SIGACTION) && defined(HAVE_SIGEMPTYSET)

/* NB: this really isn't safe, but suffices for experimentation for now.
   In due course just set a flag and do this after the return.  OTOH,
   if we do want to bail out with a core dump, need to do that here.

   2005-12-17 BDR */

static unsigned char ConsoleBuf[CONSOLE_BUFFER_SIZE];

static void sigactionSegv(int signum, siginfo_t *ip, void *context)
{
    char *s;

    /* First check for stack overflow if we know the stack position.
       We assume anything within 16Mb beyond the stack end is a stack overflow.
     */
    if(signum == SIGSEGV && (ip != (siginfo_t *)0) &&
       (intptr_t) R_CStackStart != -1) {
	uintptr_t addr = (uintptr_t) ip->si_addr;
	intptr_t diff = (R_CStackDir > 0) ? R_CStackStart - addr:
	    addr - R_CStackStart;
	uintptr_t upper = 0x1000000;  /* 16Mb */
	if((intptr_t) R_CStackLimit != -1) upper += R_CStackLimit;
	if(diff > 0 && diff < upper) {
	    REprintf(_("Error: segfault from C stack overflow\n"));
#if defined(linux) || defined(__linux__) || defined(__sun) || defined(sun)
	    sigset_t ss;
	    sigaddset(&ss, signum);
	    sigprocmask(SIG_UNBLOCK, &ss, NULL);
#endif
	    jump_to_toplevel();
	}
    }

    /* need to take off stack checking as stack base has changed */
    R_CStackLimit = (uintptr_t)-1;

    /* Do not translate these messages */
    REprintf("\n *** caught %s ***\n",
	     signum == SIGILL ? "illegal operation" :
	     signum == SIGBUS ? "bus error" : "segfault");
    if(ip != (siginfo_t *)0) {
	if(signum == SIGILL) {

	    switch(ip->si_code) {
#ifdef ILL_ILLOPC
	    case ILL_ILLOPC:
		s = "illegal opcode";
		break;
#endif
#ifdef ILL_ILLOPN
	    case ILL_ILLOPN:
		s = "illegal operand";
		break;
#endif
#ifdef ILL_ILLADR
	    case ILL_ILLADR:
		s = "illegal addressing mode";
		break;
#endif
#ifdef ILL_ILLTRP
	    case ILL_ILLTRP:
		s = "illegal trap";
		break;
#endif
#ifdef ILL_COPROC
	    case ILL_COPROC:
		s = "coprocessor error";
		break;
#endif
	    default:
		s = "unknown";
		break;
	    }
	} else if(signum == SIGBUS)
	    switch(ip->si_code) {
#ifdef BUS_ADRALN
	    case BUS_ADRALN:
		s = "invalid alignment";
		break;
#endif
#ifdef BUS_ADRERR /* not on macOS, apparently */
	    case BUS_ADRERR:
		s = "non-existent physical address";
		break;
#endif
#ifdef BUS_OBJERR /* not on macOS, apparently */
	    case BUS_OBJERR:
		s = "object specific hardware error";
		break;
#endif
	    default:
		s = "unknown";
		break;
	    }
	else
	    switch(ip->si_code) {
#ifdef SEGV_MAPERR
	    case SEGV_MAPERR:
		s = "memory not mapped";
		break;
#endif
#ifdef SEGV_ACCERR
	    case SEGV_ACCERR:
		s = "invalid permissions";
		break;
#endif
	    default:
		s = "unknown";
		break;
	    }
	REprintf("address %p, cause '%s'\n", ip->si_addr, s);
    }
    {   /* A simple customized print of the traceback */
	SEXP trace, p, q;
	int line = 1, i;
	PROTECT(trace = R_GetTraceback(0));
	if(trace != R_NilValue) {
	    REprintf("\nTraceback:\n");
	    for(p = trace; p != R_NilValue; p = CDR(p), line++) {
		q = CAR(p); /* a character vector */
		REprintf("%2d: ", line);
		for(i = 0; i < LENGTH(q); i++)
		    REprintf("%s", CHAR(STRING_ELT(q, i)));
		REprintf("\n");
	    }
	    UNPROTECT(1);
	}
    }
    if(R_Interactive) {
	REprintf("\nPossible actions:\n1: %s\n2: %s\n3: %s\n4: %s\n",
		 "abort (with core dump, if enabled)",
		 "normal R exit",
		 "exit R without saving workspace",
		 "exit R saving workspace");
	while(1) {
	    if(R_ReadConsole("Selection: ", ConsoleBuf, CONSOLE_BUFFER_SIZE,
			     0) > 0) {
		if(ConsoleBuf[0] == '1') break;
		if(ConsoleBuf[0] == '2') R_CleanUp(SA_DEFAULT, 0, 1);
		if(ConsoleBuf[0] == '3') R_CleanUp(SA_NOSAVE, 70, 0);
		if(ConsoleBuf[0] == '4') R_CleanUp(SA_SAVE, 71, 0);
	    }
	}
	REprintf("R is aborting now ...\n");
    }
    else // non-interactively :
	REprintf("An irrecoverable exception occurred. R is aborting now ...\n");
    R_CleanTempDir();
    /* now do normal behaviour, e.g. core dump */
    signal(signum, SIG_DFL);
    raise(signum);
}

#ifndef SIGSTKSZ
# define SIGSTKSZ 8192    /* just a guess */
#endif

#ifdef HAVE_STACK_T
static stack_t sigstk;
#else
static struct sigaltstack sigstk;
#endif
static void *signal_stack;

#define R_USAGE 100000 /* Just a guess */
static void init_signal_handlers(void)
{
    /* <FIXME> may need to reinstall this if we do recover. */
    struct sigaction sa;
    signal_stack = malloc(SIGSTKSZ + R_USAGE);
    if (signal_stack != NULL) {
	sigstk.ss_sp = signal_stack;
	sigstk.ss_size = SIGSTKSZ + R_USAGE;
	sigstk.ss_flags = 0;
	if(sigaltstack(&sigstk, NULL) < 0)
	    warning("failed to set alternate signal stack");
    } else
	warning("failed to allocate alternate signal stack");
    sa.sa_sigaction = sigactionSegv;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
    sigaction(SIGSEGV, &sa, NULL);
    sigaction(SIGILL, &sa, NULL);
#ifdef SIGBUS
    sigaction(SIGBUS, &sa, NULL);
#endif

    signal(SIGINT,  handleInterrupt);
    signal(SIGUSR1, onsigusr1);
    signal(SIGUSR2, onsigusr2);
    signal(SIGPIPE, handlePipe);
}

#else /* not sigaltstack and sigaction and sigemptyset*/
static void init_signal_handlers(void)
{
    signal(SIGINT,  handleInterrupt);
    signal(SIGUSR1, onsigusr1);
    signal(SIGUSR2, onsigusr2);
#ifndef Win32
    signal(SIGPIPE, handlePipe);
#else
    signal(SIGSEGV, win32_segv);
    signal(SIGILL, win32_segv);
#endif
}
#endif


static void R_LoadProfile(FILE *fparg, SEXP env)
{
    FILE * volatile fp = fparg; /* is this needed? */
    if (fp != NULL) {
	if (SETJMP(R_Toplevel.cjmpbuf))
	    check_session_exit();
	else {
	    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
	    R_ReplFile(fp, env);
	}
	fclose(fp);
    }
}


int R_SignalHandlers = 1;  /* Exposed in R_interface.h */

const char* get_workspace_name();  /* from startup.c */

void attribute_hidden BindDomain(char *R_Home)
{
#ifdef ENABLE_NLS
    char localedir[PATH_MAX+20];
    setlocale(LC_MESSAGES,"");
    textdomain(PACKAGE);
    char *p = getenv("R_TRANSLATIONS");
    if (p) snprintf(localedir, PATH_MAX+20, "%s", p);
    else snprintf(localedir, PATH_MAX+20, "%s/library/translations", R_Home);
    bindtextdomain(PACKAGE, localedir); // PACKAGE = DOMAIN = "R"
    bindtextdomain("R-base", localedir);
# ifdef _WIN32
    bindtextdomain("RGui", localedir);
# endif
#endif
}

void setup_Rmainloop(void)
{
    volatile int doneit;
    volatile SEXP baseEnv;
    SEXP cmd;
    char deferred_warnings[11][250];
    volatile int ndeferred_warnings = 0;

#if 0 
    /* testing stack base and size detection */
    printf("stack limit %ld, start %lx dir %d \n",
	(unsigned long) R_CStackLimit,
        (unsigned long) R_CStackStart,
	R_CStackDir);
    uintptr_t firstb = R_CStackStart - R_CStackDir;
    printf("first accessible byte %lx\n", (unsigned long) firstb);
    if (R_CStackLimit != (uintptr_t)(-1)) {
        uintptr_t lastb = R_CStackStart - R_CStackDir * R_CStackLimit;
	printf("last accessible byte %lx\n", (unsigned long) lastb);
    }
    printf("accessing first byte...\n");
    volatile char dummy = *(char *)firstb;
    if (R_CStackLimit != (uintptr_t)(-1)) {
	printf("accessing all bytes...\n");
	/* have to access all bytes in order to map stack, e.g. on Linux */
	for(uintptr_t o = 0; o < R_CStackLimit; o++)
	    /* with exact bounds, o==-1 and o==R_CStackLimit will segfault */
	    dummy = *((char *)firstb - R_CStackDir * o);
    }
#endif

    /* In case this is a silly limit: 2^32 -3 has been seen and
     * casting to intptr_r relies on this being smaller than 2^31 on a
     * 32-bit platform. */
    if(R_CStackLimit > 100000000U)
	R_CStackLimit = (uintptr_t)-1;
    /* make sure we have enough head room to handle errors */
    if(R_CStackLimit != -1)
	R_CStackLimit = (uintptr_t)(0.95 * R_CStackLimit);

    InitConnections(); /* needed to get any output at all */

    /* Initialize the interpreter's internal structures. */

#ifdef HAVE_LOCALE_H
#ifdef Win32
    {
	char *p, Rlocale[1000]; /* Windows' locales can be very long */
	p = getenv("LC_ALL");
	strncpy(Rlocale, p ? p : "", 1000);
	Rlocale[1000 - 1] = '\0';
	if(!(p = getenv("LC_CTYPE"))) p = Rlocale;
	/* We'd like to use warning, but need to defer.
	   Also cannot translate. */
	if(!setlocale(LC_CTYPE, p))
	    snprintf(deferred_warnings[ndeferred_warnings++], 250,
		     "Setting LC_CTYPE=%s failed\n", p);
	if((p = getenv("LC_COLLATE"))) {
	    if(!setlocale(LC_COLLATE, p))
		snprintf(deferred_warnings[ndeferred_warnings++], 250,
			 "Setting LC_COLLATE=%s failed\n", p);
	} else setlocale(LC_COLLATE, Rlocale);
	if((p = getenv("LC_TIME"))) {
	    if(!setlocale(LC_TIME, p))
		snprintf(deferred_warnings[ndeferred_warnings++], 250,
			 "Setting LC_TIME=%s failed\n", p);
	} else setlocale(LC_TIME, Rlocale);
	if((p = getenv("LC_MONETARY"))) {
	    if(!setlocale(LC_MONETARY, p))
		snprintf(deferred_warnings[ndeferred_warnings++], 250,
			 "Setting LC_MONETARY=%s failed\n", p);
	} else setlocale(LC_MONETARY, Rlocale);
	/* Windows does not have LC_MESSAGES */

	/* We set R_ARCH here: Unix does it in the shell front-end */
	char Rarch[30];
	strcpy(Rarch, "R_ARCH=/");
	strcat(Rarch, R_ARCH);
	putenv(Rarch);
    }
#else /* not Win32 */
    if(!setlocale(LC_CTYPE, ""))
	snprintf(deferred_warnings[ndeferred_warnings++], 250,
		 "Setting LC_CTYPE failed, using \"C\"\n");
    if(!setlocale(LC_COLLATE, ""))
	snprintf(deferred_warnings[ndeferred_warnings++], 250,
		 "Setting LC_COLLATE failed, using \"C\"\n");
    if(!setlocale(LC_TIME, ""))
	snprintf(deferred_warnings[ndeferred_warnings++], 250,
		 "Setting LC_TIME failed, using \"C\"\n");
#ifdef ENABLE_NLS
    if(!setlocale(LC_MESSAGES, ""))
	snprintf(deferred_warnings[ndeferred_warnings++], 250,
		 "Setting LC_MESSAGES failed, using \"C\"\n");
#endif
    /* NB: we do not set LC_NUMERIC */
#ifdef LC_MONETARY
    if(!setlocale(LC_MONETARY, ""))
	snprintf(deferred_warnings[ndeferred_warnings++], 250,
		 "Setting LC_MONETARY failed, using \"C\"\n");
#endif
#ifdef LC_PAPER
    if(!setlocale(LC_PAPER, ""))
	snprintf(deferred_warnings[ndeferred_warnings++], 250,
		 "Setting LC_PAPER failed, using \"C\"\n");
#endif
#ifdef LC_MEASUREMENT
    if(!setlocale(LC_MEASUREMENT, ""))
	snprintf(deferred_warnings[ndeferred_warnings++], 250,
		 "Setting LC_MEASUREMENT failed, using \"C\"\n");
#endif
#endif /* not Win32 */
#endif

    /* make sure srand is called before R_tmpnam, PR#14381 */
    srand(TimeToSeed());

    InitArithmetic();
    InitTempDir(); /* must be before InitEd */
    InitMemory();
    InitStringHash(); /* must be before InitNames */
    InitBaseEnv();
    InitNames(); /* must be after InitBaseEnv to use R_EmptyEnv */
    InitParser();  /* must be after InitMemory, InitNames */
    InitGlobalEnv();
    InitDynload();
    InitOptions();
    InitEd();
    InitGraphics();
    InitTypeTables(); /* must be before InitS3DefaultTypes */
    InitS3DefaultTypes();
    PrintDefaults();

    R_Is_Running = 1;
    R_check_locale();

    /* Initialize the global context for error handling. */
    /* This provides a target for any non-local gotos */
    /* which occur during error handling */

    R_Toplevel.nextcontext = NULL;
    R_Toplevel.callflag = CTXT_TOPLEVEL;
    R_Toplevel.cstacktop = 0;
    R_Toplevel.gcenabled = R_GCEnabled;
    R_Toplevel.promargs = R_NilValue;
    R_Toplevel.callfun = R_NilValue;
    R_Toplevel.call = R_NilValue;
    R_Toplevel.cloenv = R_BaseEnv;
    R_Toplevel.sysparent = R_BaseEnv;
    R_Toplevel.conexit = R_NilValue;
    R_Toplevel.vmax = NULL;
    R_Toplevel.nodestack = R_BCNodeStackTop;
    R_Toplevel.cend = NULL;
    R_Toplevel.cenddata = NULL;
    R_Toplevel.intsusp = FALSE;
    R_Toplevel.handlerstack = R_HandlerStack;
    R_Toplevel.restartstack = R_RestartStack;
    R_Toplevel.srcref = R_NilValue;
    R_Toplevel.prstack = NULL;
    R_Toplevel.returnValue = NULL;
    R_Toplevel.evaldepth = 0;
    R_Toplevel.browserfinish = 0;
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    R_ExitContext = NULL;

    R_Warnings = R_NilValue;

    /* This is the same as R_BaseEnv, but this marks the environment
       of functions as the namespace and not the package. */
    baseEnv = R_BaseNamespace;

    /* Set up some global variables */
    Init_R_Variables(baseEnv);

    /* On initial entry we open the base language package and begin by
       running the repl on it.
       If there is an error we pass on to the repl.
       Perhaps it makes more sense to quit gracefully?
    */

#ifdef RMIN_ONLY
    /* This is intended to support a minimal build for experimentation. */
    if (R_SignalHandlers) init_signal_handlers();
#else
    FILE *fp = R_OpenLibraryFile("base");
    if (fp == NULL)
	R_Suicide(_("unable to open the base package\n"));

    doneit = 0;
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    if (R_SignalHandlers) init_signal_handlers();
    if (!doneit) {
	doneit = 1;
	R_ReplFile(fp, baseEnv);
    }
    fclose(fp);
#endif

    /* This is where we source the system-wide, the site's and the
       user's profile (in that order).  If there is an error, we
       drop through to further processing.
    */
    R_IoBufferInit(&R_ConsoleIob);
    R_LoadProfile(R_OpenSysInitFile(), baseEnv);
    /* These are the same bindings, so only lock them once */
    R_LockEnvironment(R_BaseNamespace, TRUE);
#ifdef NOTYET
    /* methods package needs to trample here */
    R_LockEnvironment(R_BaseEnv, TRUE);
#endif
    /* At least temporarily unlock some bindings used in graphics */
    R_unLockBinding(R_DeviceSymbol, R_BaseEnv);
    R_unLockBinding(R_DevicesSymbol, R_BaseEnv);
    R_unLockBinding(install(".Library.site"), R_BaseEnv);

    /* require(methods) if it is in the default packages */
    doneit = 0;
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    if (!doneit) {
	doneit = 1;
	PROTECT(cmd = install(".OptRequireMethods"));
	R_CurrentExpr = findVar(cmd, R_GlobalEnv);
	if (R_CurrentExpr != R_UnboundValue &&
	    TYPEOF(R_CurrentExpr) == CLOSXP) {
		PROTECT(R_CurrentExpr = lang1(cmd));
		R_CurrentExpr = eval(R_CurrentExpr, R_GlobalEnv);
		UNPROTECT(1);
	}
	UNPROTECT(1);
    }

    if (strcmp(R_GUIType, "Tk") == 0) {
	char buf[PATH_MAX];

	snprintf(buf, PATH_MAX, "%s/library/tcltk/exec/Tk-frontend.R", R_Home);
	R_LoadProfile(R_fopen(buf, "r"), R_GlobalEnv);
    }

    /* Print a platform and version dependent greeting and a pointer to
     * the copyleft.
     */
    if(!R_Quiet) PrintGreeting();

    R_LoadProfile(R_OpenSiteFile(), baseEnv);
    R_LockBinding(install(".Library.site"), R_BaseEnv);
    R_LoadProfile(R_OpenInitFile(), R_GlobalEnv);

    /* This is where we try to load a user's saved data.
       The right thing to do here is very platform dependent.
       E.g. under Unix we look in a special hidden file and on the Mac
       we look in any documents which might have been double clicked on
       or dropped on the application.
    */
    doneit = 0;
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    if (!doneit) {
	doneit = 1;
	R_InitialData();
    }
    else {
	if (SETJMP(R_Toplevel.cjmpbuf))
	    check_session_exit();
	else {
    	    warning(_("unable to restore saved data in %s\n"), get_workspace_name());
	}
    }

    /* Initial Loading is done.
       At this point we try to invoke the .First Function.
       If there is an error we continue. */

    doneit = 0;
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    if (!doneit) {
	doneit = 1;
	PROTECT(cmd = install(".First"));
	R_CurrentExpr = findVar(cmd, R_GlobalEnv);
	if (R_CurrentExpr != R_UnboundValue &&
	    TYPEOF(R_CurrentExpr) == CLOSXP) {
		PROTECT(R_CurrentExpr = lang1(cmd));
		R_CurrentExpr = eval(R_CurrentExpr, R_GlobalEnv);
		UNPROTECT(1);
	}
	UNPROTECT(1);
    }
    /* Try to invoke the .First.sys function, which loads the default packages.
       If there is an error we continue. */

    doneit = 0;
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    if (!doneit) {
	doneit = 1;
	PROTECT(cmd = install(".First.sys"));
	R_CurrentExpr = findVar(cmd, baseEnv);
	if (R_CurrentExpr != R_UnboundValue &&
	    TYPEOF(R_CurrentExpr) == CLOSXP) {
		PROTECT(R_CurrentExpr = lang1(cmd));
		R_CurrentExpr = eval(R_CurrentExpr, R_GlobalEnv);
		UNPROTECT(1);
	}
	UNPROTECT(1);
    }
    {
	int i;
	for(i = 0 ; i < ndeferred_warnings; i++)
	    warning(deferred_warnings[i]);
    }
    if (R_CollectWarnings) {
	REprintf(_("During startup - "));
	PrintWarnings();
    }
    if(R_Verbose)
	REprintf(" ending setup_Rmainloop(): R_Interactive = %d {main.c}\n",
		 R_Interactive);

    /* trying to do this earlier seems to run into bootstrapping issues. */
    doneit = 0;
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    if (!doneit) {
	doneit = 1;
	R_init_jit_enabled();
    } else
	R_Suicide(_("unable to initialize the JIT\n"));
    R_Is_Running = 2;
}

extern SA_TYPE SaveAction; /* from src/main/startup.c */

static void end_Rmainloop(void)
{
    /* refrain from printing trailing '\n' in slave mode */
    if (!R_Slave)
	Rprintf("\n");
    /* run the .Last function. If it gives an error, will drop back to main
       loop. */
    R_CleanUp(SA_DEFAULT, 0, 1);
}

void run_Rmainloop(void)
{
    /* Here is the real R read-eval-loop. */
    /* We handle the console until end-of-file. */
    if (SETJMP(R_Toplevel.cjmpbuf))
	check_session_exit();
    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    R_ReplConsole(R_GlobalEnv, 0, 0);
    end_Rmainloop(); /* must go here */
}

void mainloop(void)
{
    setup_Rmainloop();
    run_Rmainloop();
}

/*this functionality now appears in 3
  places-jump_to_toplevel/profile/here */

void attribute_hidden printwhere(void)
{
  RCNTXT *cptr;
  int lct = 1;

  for (cptr = R_GlobalContext; cptr; cptr = cptr->nextcontext) {
    if ((cptr->callflag & (CTXT_FUNCTION | CTXT_BUILTIN)) &&
	(TYPEOF(cptr->call) == LANGSXP)) {
	Rprintf("where %d", lct++);
	SEXP sref;
	if (cptr->srcref == R_InBCInterpreter)
	    sref = R_findBCInterpreterSrcref(cptr);
	else
	    sref = cptr->srcref;
	SrcrefPrompt("", sref);
	PrintValue(cptr->call);
    }
  }
  Rprintf("\n");
}

static void printBrowserHelp(void)
{
    Rprintf("n          next\n");
    Rprintf("s          step into\n");
    Rprintf("f          finish\n");
    Rprintf("c or cont  continue\n");
    Rprintf("Q          quit\n");
    Rprintf("where      show stack\n");
    Rprintf("help       show help\n");
    Rprintf("<expr>     evaluate expression\n");
}

static int ParseBrowser(SEXP CExpr, SEXP rho)
{
    int rval = 0;
    if (isSymbol(CExpr)) {
	const char *expr = CHAR(PRINTNAME(CExpr));
	if (!strcmp(expr, "c") || !strcmp(expr, "cont")) {
	    rval = 1;
	    SET_RDEBUG(rho, 0);
	} else if (!strcmp(expr, "f")) {
	    rval = 1;
	    RCNTXT *cntxt = R_GlobalContext;
	    while (cntxt != R_ToplevelContext
		      && !(cntxt->callflag & (CTXT_RETURN | CTXT_LOOP))) {
		cntxt = cntxt->nextcontext;
	    }
	    cntxt->browserfinish = 1;
	    SET_RDEBUG(rho, 1);
	    R_BrowserLastCommand = 'f';
	} else if (!strcmp(expr, "help")) {
	    rval = 2;
	    printBrowserHelp();
	} else if (!strcmp(expr, "n")) {
	    rval = 1;
	    SET_RDEBUG(rho, 1);
	    R_BrowserLastCommand = 'n';
	} else if (!strcmp(expr, "Q")) {

	    /* this is really dynamic state that should be managed as such */
	    SET_RDEBUG(rho, 0); /*PR#1721*/

	    jump_to_toplevel();
	} else if (!strcmp(expr, "s")) {
	    rval = 1;
	    SET_RDEBUG(rho, 1);
	    R_BrowserLastCommand = 's';
	} else if (!strcmp(expr, "where")) {
	    rval = 2;
	    printwhere();
	    /* SET_RDEBUG(rho, 1); */
	} else if (!strcmp(expr, "r")) {
	    SEXP hooksym = install(".tryResumeInterrupt");
	    if (SYMVALUE(hooksym) != R_UnboundValue) {
		SEXP hcall;
		R_Busy(1);
		PROTECT(hcall = LCONS(hooksym, R_NilValue));
		eval(hcall, R_GlobalEnv);
		UNPROTECT(1);
	    }
	}
    }

    return rval;
}

/* There's another copy of this in eval.c */
static void PrintCall(SEXP call, SEXP rho)
{
    int old_bl = R_BrowseLines,
	blines = asInteger(GetOption1(install("deparse.max.lines")));
    if(blines != NA_INTEGER && blines > 0)
	R_BrowseLines = blines;

    R_PrintData pars;
    PrintInit(&pars, rho);
    PrintValueRec(call, &pars);

    R_BrowseLines = old_bl;
}

/* browser(text = "", condition = NULL, expr = TRUE, skipCalls = 0L)
 * ------- but also called from ./eval.c */
SEXP attribute_hidden do_browser(SEXP call, SEXP op, SEXP args, SEXP rho)
{
    RCNTXT *saveToplevelContext;
    RCNTXT *saveGlobalContext;
    RCNTXT thiscontext, returncontext, *cptr;
    int savestack, browselevel;
    SEXP ap, topExp, argList;

    /* Cannot call checkArity(op, args), because "op" may be a closure  */
    /* or a primitive other than "browser".  */

    /* argument matching */
    PROTECT(ap = list4(R_NilValue, R_NilValue, R_NilValue, R_NilValue));
    SET_TAG(ap,  install("text"));
    SET_TAG(CDR(ap), install("condition"));
    SET_TAG(CDDR(ap), install("expr"));
    SET_TAG(CDDDR(ap), install("skipCalls"));
    argList = matchArgs_RC(ap, args, call);
    UNPROTECT(1);
    PROTECT(argList);
    /* substitute defaults */
    if(CAR(argList) == R_MissingArg)
	SETCAR(argList, mkString(""));
    if(CADR(argList) == R_MissingArg)
	SETCAR(CDR(argList), R_NilValue);
    if(CADDR(argList) == R_MissingArg)
	SETCAR(CDDR(argList), ScalarLogical(1));
    if(CADDDR(argList) == R_MissingArg)
	SETCAR(CDDDR(argList), ScalarInteger(0));

    /* return if 'expr' is not TRUE */
    if( !asLogical(CADDR(argList)) ) {
	UNPROTECT(1);
	return R_NilValue;
    }

    /* Save the evaluator state information */
    /* so that it can be restored on exit. */

    browselevel = countContexts(CTXT_BROWSER, 1);
    savestack = R_PPStackTop;
    PROTECT(topExp = R_CurrentExpr);
    saveToplevelContext = R_ToplevelContext;
    saveGlobalContext = R_GlobalContext;

    if (!RDEBUG(rho)) {
	int skipCalls = asInteger(CADDDR(argList));
	cptr = R_GlobalContext;
	while ( ( !(cptr->callflag & CTXT_FUNCTION) || skipCalls--)
		&& cptr->callflag )
	    cptr = cptr->nextcontext;
	Rprintf("Called from: ");
	if( cptr != R_ToplevelContext ) {
	    PrintCall(cptr->call, rho);
	    SET_RDEBUG(cptr->cloenv, 1);
	} else
	    Rprintf("top level \n");

	R_BrowseLines = 0;
    }

    R_ReturnedValue = R_NilValue;

    /* Here we establish two contexts.  The first */
    /* of these provides a target for return */
    /* statements which a user might type at the */
    /* browser prompt.  The (optional) second one */
    /* acts as a target for error returns. */

    begincontext(&returncontext, CTXT_BROWSER, call, rho,
		 R_BaseEnv, argList, R_NilValue);
    if (!SETJMP(returncontext.cjmpbuf)) {
	begincontext(&thiscontext, CTXT_RESTART, R_NilValue, rho,
		     R_BaseEnv, R_NilValue, R_NilValue);
	if (SETJMP(thiscontext.cjmpbuf)) {
	    SET_RESTART_BIT_ON(thiscontext.callflag);
	    R_ReturnedValue = R_NilValue;
	    R_Visible = FALSE;
	}
	R_GlobalContext = &thiscontext;
	R_InsertRestartHandlers(&thiscontext, "browser");
	R_ReplConsole(rho, savestack, browselevel+1);
	endcontext(&thiscontext);
    }
    endcontext(&returncontext);

    /* Reset the interpreter state. */

    R_CurrentExpr = topExp;
    UNPROTECT(1);
    R_PPStackTop = savestack;
    UNPROTECT(1);
    R_CurrentExpr = topExp;
    R_ToplevelContext = saveToplevelContext;
    R_GlobalContext = saveGlobalContext;
    return R_ReturnedValue;
}

void R_dot_Last(void)
{
    SEXP cmd;

    /* Run the .Last function. */
    /* Errors here should kick us back into the repl. */

    R_GlobalContext = R_ToplevelContext = R_SessionContext = &R_Toplevel;
    PROTECT(cmd = install(".Last"));
    R_CurrentExpr = findVar(cmd, R_GlobalEnv);
    if (R_CurrentExpr != R_UnboundValue && TYPEOF(R_CurrentExpr) == CLOSXP) {
	PROTECT(R_CurrentExpr = lang1(cmd));
	R_CurrentExpr = eval(R_CurrentExpr, R_GlobalEnv);
	UNPROTECT(1);
    }
    UNPROTECT(1);
    PROTECT(cmd = install(".Last.sys"));
    R_CurrentExpr = findVar(cmd, R_BaseNamespace);
    if (R_CurrentExpr != R_UnboundValue && TYPEOF(R_CurrentExpr) == CLOSXP) {
	PROTECT(R_CurrentExpr = lang1(cmd));
	R_CurrentExpr = eval(R_CurrentExpr, R_GlobalEnv);
	UNPROTECT(1);
    }
    UNPROTECT(1);
}

SEXP attribute_hidden do_quit(SEXP call, SEXP op, SEXP args, SEXP rho)
{
    const char *tmp;
    SA_TYPE ask=SA_DEFAULT;
    int status, runLast;

    checkArity(op, args);
    /* if there are any browser contexts active don't quit */
    if(countContexts(CTXT_BROWSER, 1)) {
	warning(_("cannot quit from browser"));
	return R_NilValue;
    }
    if( !isString(CAR(args)) )
	error(_("one of \"yes\", \"no\", \"ask\" or \"default\" expected."));
    tmp = CHAR(STRING_ELT(CAR(args), 0)); /* ASCII */
    if( !strcmp(tmp, "ask") ) {
	ask = SA_SAVEASK;
	if(!R_Interactive)
	    warning(_("save=\"ask\" in non-interactive use: command-line default will be used"));
    } else if( !strcmp(tmp, "no") )
	ask = SA_NOSAVE;
    else if( !strcmp(tmp, "yes") )
	ask = SA_SAVE;
    else if( !strcmp(tmp, "default") )
	ask = SA_DEFAULT;
    else
	error(_("unrecognized value of 'save'"));
    status = asInteger(CADR(args));
    if (status == NA_INTEGER) {
	warning(_("invalid 'status', 0 assumed"));
	status = 0;
    }
    runLast = asLogical(CADDR(args));
    if (runLast == NA_LOGICAL) {
	warning(_("invalid 'runLast', FALSE assumed"));
	runLast = 0;
    }
    /* run the .Last function. If it gives an error, will drop back to main
       loop. */
    R_CleanUp(ask, status, runLast);
    exit(0);
    /*NOTREACHED*/
}


#include <R_ext/Callbacks.h>

static R_ToplevelCallbackEl *Rf_ToplevelTaskHandlers = NULL;

/**
  This is the C-level entry point for registering a handler
  that is to be called when each top-level task completes.

  Perhaps we need names to make removing them handlers easier
  since they could be more identified by an invariant (rather than
  position).
 */
R_ToplevelCallbackEl *
Rf_addTaskCallback(R_ToplevelCallback cb, void *data,
		   void (*finalizer)(void *), const char *name, int *pos)
{
    int which;
    R_ToplevelCallbackEl *el;
    el = (R_ToplevelCallbackEl *) malloc(sizeof(R_ToplevelCallbackEl));
    if(!el)
	error(_("cannot allocate space for toplevel callback element"));

    el->data = data;
    el->cb = cb;
    el->next = NULL;
    el->finalizer = finalizer;

    if(Rf_ToplevelTaskHandlers == NULL) {
	Rf_ToplevelTaskHandlers = el;
	which = 0;
    } else {
	R_ToplevelCallbackEl *tmp;
	tmp = Rf_ToplevelTaskHandlers;
	which = 1;
	while(tmp->next) {
	    which++;
	    tmp = tmp->next;
	}
	tmp->next = el;
    }

    if(!name) {
	char buf[20];
	snprintf(buf, 20, "%d", which+1);
	el->name = strdup(buf);
    } else
	el->name = strdup(name);

    if(pos)
	*pos = which;

    return(el);
}

Rboolean
Rf_removeTaskCallbackByName(const char *name)
{
    R_ToplevelCallbackEl *el = Rf_ToplevelTaskHandlers, *prev = NULL;
    Rboolean status = TRUE;

    if(!Rf_ToplevelTaskHandlers) {
	return(FALSE); /* error("there are no task callbacks registered"); */
    }

    while(el) {
	if(strcmp(el->name, name) == 0) {
	    if(prev == NULL) {
		Rf_ToplevelTaskHandlers = el->next;
	    } else {
		prev->next = el->next;
	    }
	    break;
	}
	prev = el;
	el = el->next;
    }
    if(el) {
	if(el->finalizer)
	    el->finalizer(el->data);
	free(el->name);
	free(el);
    } else {
	status = FALSE;
    }
    return(status);
}

/**
  Remove the top-level task handler/callback identified by
  its position in the list of callbacks.
 */
Rboolean
Rf_removeTaskCallbackByIndex(int id)
{
    R_ToplevelCallbackEl *el = Rf_ToplevelTaskHandlers, *tmp = NULL;
    Rboolean status = TRUE;

    if(id < 0)
	error(_("negative index passed to R_removeTaskCallbackByIndex"));

    if(Rf_ToplevelTaskHandlers) {
	if(id == 0) {
	    tmp = Rf_ToplevelTaskHandlers;
	    Rf_ToplevelTaskHandlers = Rf_ToplevelTaskHandlers->next;
	} else {
	    int i = 0;
	    while(el && i < (id-1)) {
		el = el->next;
		i++;
	    }

	    if(i == (id -1) && el) {
		tmp = el->next;
		el->next = (tmp ? tmp->next : NULL);
	    }
	}
    }
    if(tmp) {
	if(tmp->finalizer)
	    tmp->finalizer(tmp->data);
	free(tmp->name);
	free(tmp);
    } else {
	status = FALSE;
    }

    return(status);
}


/**
  R-level entry point to remove an entry from the
  list of top-level callbacks. 'which' should be an
  integer and give us the 0-based index of the element
  to be removed from the list.

  @see Rf_RemoveToplevelCallbackByIndex(int)
 */
SEXP
R_removeTaskCallback(SEXP which)
{
    int id;
    Rboolean val;

    if(TYPEOF(which) == STRSXP) {
	if (LENGTH(which) == 0)
	    val = FALSE;
	else
	    val = Rf_removeTaskCallbackByName(CHAR(STRING_ELT(which, 0)));
    } else {
	id = asInteger(which);
	if (id != NA_INTEGER) val = Rf_removeTaskCallbackByIndex(id - 1);
	else val = FALSE;
    }
    return ScalarLogical(val);
}

SEXP
R_getTaskCallbackNames(void)
{
    SEXP ans;
    R_ToplevelCallbackEl *el;
    int n = 0;

    el = Rf_ToplevelTaskHandlers;
    while(el) {
	n++;
	el = el->next;
    }
    PROTECT(ans = allocVector(STRSXP, n));
    n = 0;
    el = Rf_ToplevelTaskHandlers;
    while(el) {
	SET_STRING_ELT(ans, n, mkChar(el->name));
	n++;
	el = el->next;
    }
    UNPROTECT(1);
    return(ans);
}

/**
  Invokes each of the different handlers giving the
  top-level expression that was just evaluated,
  the resulting value from the evaluation, and
  whether the task succeeded. The last may be useful
  if a handler is also called as part of the error handling.
  We also have information about whether the result was printed or not.
  We currently do not pass this to the handler.
 */

  /* Flag to ensure that the top-level handlers aren't called recursively.
     Simple state to indicate that they are currently being run. */
static Rboolean Rf_RunningToplevelHandlers = FALSE;

/* This is not used in R and in no header */
void
Rf_callToplevelHandlers(SEXP expr, SEXP value, Rboolean succeeded,
			Rboolean visible)
{
    R_ToplevelCallbackEl *h, *prev = NULL;
    Rboolean again;

    if(Rf_RunningToplevelHandlers == TRUE)
	return;

    h = Rf_ToplevelTaskHandlers;
    Rf_RunningToplevelHandlers = TRUE;
    while(h) {
	again = (h->cb)(expr, value, succeeded, visible, h->data);
	if(R_CollectWarnings) {
	    REprintf(_("warning messages from top-level task callback '%s'\n"),
		     h->name);
	    PrintWarnings();
	}
	if(again) {
	    prev = h;
	    h = h->next;
	} else {
	    R_ToplevelCallbackEl *tmp;
	    tmp = h;
	    if(prev)
		prev->next = h->next;
	    h = h->next;
	    if(tmp == Rf_ToplevelTaskHandlers)
		Rf_ToplevelTaskHandlers = h;
	    if(tmp->finalizer)
		tmp->finalizer(tmp->data);
	    free(tmp);
	}
    }

    Rf_RunningToplevelHandlers = FALSE;
}


Rboolean
R_taskCallbackRoutine(SEXP expr, SEXP value, Rboolean succeeded,
		      Rboolean visible, void *userData)
{
    SEXP f = (SEXP) userData;
    SEXP e, tmp, val, cur;
    int errorOccurred;
    Rboolean again, useData = LOGICAL(VECTOR_ELT(f, 2))[0];

    PROTECT(e = allocVector(LANGSXP, 5 + useData));
    SETCAR(e, VECTOR_ELT(f, 0));
    cur = CDR(e);
    SETCAR(cur, tmp = allocVector(LANGSXP, 2));
	SETCAR(tmp, lang3(R_DoubleColonSymbol, R_BaseSymbol, R_QuoteSymbol));
	SETCAR(CDR(tmp), expr);
    cur = CDR(cur);
    SETCAR(cur, value);
    cur = CDR(cur);
    SETCAR(cur, ScalarLogical(succeeded));
    cur = CDR(cur);
    SETCAR(cur, tmp = ScalarLogical(visible));
    if(useData) {
	cur = CDR(cur);
	SETCAR(cur, VECTOR_ELT(f, 1));
    }

    val = R_tryEval(e, NULL, &errorOccurred);
    UNPROTECT(1); /* e */
    if(!errorOccurred) {
	PROTECT(val);
	if(TYPEOF(val) != LGLSXP) {
	      /* It would be nice to identify the function. */
	    warning(_("top-level task callback did not return a logical value"));
	}
	again = asLogical(val);
	UNPROTECT(1);
    } else {
	/* warning("error occurred in top-level task callback\n"); */
	again = FALSE;
    }
    return(again);
}

SEXP
R_addTaskCallback(SEXP f, SEXP data, SEXP useData, SEXP name)
{
    SEXP internalData;
    SEXP index;
    R_ToplevelCallbackEl *el;
    const char *tmpName = NULL;

    internalData = allocVector(VECSXP, 3);
    R_PreserveObject(internalData);
    SET_VECTOR_ELT(internalData, 0, f);
    SET_VECTOR_ELT(internalData, 1, data);
    SET_VECTOR_ELT(internalData, 2, useData);

    if(length(name))
	tmpName = CHAR(STRING_ELT(name, 0));

    PROTECT(index = allocVector(INTSXP, 1));
    el = Rf_addTaskCallback(R_taskCallbackRoutine,  internalData,
			    (void (*)(void*)) R_ReleaseObject, tmpName,
			    INTEGER(index));

    if(length(name) == 0) {
	PROTECT(name = mkString(el->name));
	setAttrib(index, R_NamesSymbol, name);
	UNPROTECT(1);
    } else {
	setAttrib(index, R_NamesSymbol, name);
    }

    UNPROTECT(1);
    return(index);
}

#undef __MAIN__

#ifndef Win32
/* this is here solely to pull in xxxpr.o */
# include <R_ext/RS.h>
# if defined FC_LEN_T
# include <stddef.h>
void F77_SYMBOL(rwarnc)(char *msg, int *nchar, FC_LEN_T msg_len);
void attribute_hidden dummy54321(void)
{
    int nc = 5;
    F77_CALL(rwarnc)("dummy", &nc, (FC_LEN_T) 5);
}
# else
void F77_SYMBOL(rwarnc)(char *msg, int *nchar);
void attribute_hidden dummy54321(void)
{
    int nc = 5;
    F77_CALL(rwarnc)("dummy", &nc);
}
# endif
#endif