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[bpt/guile.git] / libguile / stacks.c

/* Representation of stack frame debug information
 * Copyright (C) 1996,1997 Free Software 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, 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 software; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307 USA
 *
 * As a special exception, the Free Software Foundation gives permission
 * for additional uses of the text contained in its release of GUILE.
 *
 * The exception is that, if you link the GUILE library with other files
 * to produce an executable, this does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * Your use of that executable is in no way restricted on account of
 * linking the GUILE library code into it.
 *
 * This exception does not however invalidate any other reasons why
 * the executable file might be covered by the GNU General Public License.
 *
 * This exception applies only to the code released by the
 * Free Software Foundation under the name GUILE.  If you copy
 * code from other Free Software Foundation releases into a copy of
 * GUILE, as the General Public License permits, the exception does
 * not apply to the code that you add in this way.  To avoid misleading
 * anyone as to the status of such modified files, you must delete
 * this exception notice from them.
 *
 * If you write modifications of your own for GUILE, it is your choice
 * whether to permit this exception to apply to your modifications.
 * If you do not wish that, delete this exception notice.
 *
 * The author can be reached at djurfeldt@nada.kth.se
 * Mikael Djurfeldt, SANS/NADA KTH, 10044 STOCKHOLM, SWEDEN */
\f

#include <stdio.h>
#include "_scm.h"
#include "eval.h"
#include "debug.h"
#include "continuations.h"
#include "struct.h"
#include "macros.h"
#include "procprop.h"
#include "modules.h"

#include "stacks.h"

\f
/* {Frames and stacks}
 *
 * The debugging evaluator creates debug frames on the stack.  These
 * are linked from the innermost frame and outwards.  The last frame
 * created can always be accessed as SCM_LAST_DEBUG_FRAME.
 * Continuations contain a pointer to the innermost debug frame on the
 * continuation stack.
 *
 * Each debug frame contains a set of flags and information about one
 * or more stack frames.  The case of multiple frames occurs due to
 * tail recursion.  The maximal number of stack frames which can be
 * recorded in one debug frame can be set dynamically with the debug
 * option FRAMES.
 *
 * Stack frame information is of two types: eval information (the
 * expression being evaluated and its environment) and apply
 * information (the procedure being applied and its arguments).  A
 * stack frame normally corresponds to an eval/apply pair, but macros
 * and special forms (which are implemented as macros in Guile) only
 * have eval information and apply calls leads to apply only frames.
 *
 * Since we want to record the total stack information and later
 * manipulate this data at the scheme level in the debugger, we need
 * to transform it into a new representation.  In the following code
 * section you'll find the functions implementing this data type.
 *
 * Representation:
 *
 * The stack is represented as a struct with an id slot and a tail
 * array of scm_info_frame structs.
 *
 * A frame is represented as a pair where the car contains a stack and
 * the cdr an inum.  The inum is an index to the first SCM value of
 * the scm_info_frame struct.
 *
 * Stacks
 *   Constructor
 *     make-stack
 *   Selectors
 *     stack-id
 *     stack-ref
 *   Inspector
 *     stack-length
 *
 * Frames
 *   Constructor
 *     last-stack-frame
 *   Selectors
 *     frame-number
 *     frame-source
 *     frame-procedure
 *     frame-arguments
 *     frame-previous
 *     frame-next
 *   Predicates
 *     frame-real?
 *     frame-procedure?
 *     frame-evaluating-args?
 *     frame-overflow?  */

\f

/* Some auxiliary functions for reading debug frames off the stack.
 */

/* Stacks often contain pointers to other items on the stack; for
   example, each scm_debug_frame structure contains a pointer to the
   next frame out.  When we capture a continuation, we copy the stack
   into the heap, and just leave all the pointers unchanged.  This
   makes it simple to restore the continuation --- just copy the stack
   back!  However, if we retrieve a pointer from the heap copy to
   another item that was originally on the stack, we have to add an
   offset to the pointer to discover the new referent.

   If PTR is a pointer retrieved from a continuation, whose original
   target was on the stack, and OFFSET is the appropriate offset from
   the original stack to the continuation, then RELOC_MUMBLE (PTR,
   OFFSET) is a pointer to the copy in the continuation of the
   original referent, cast to an scm_debug_MUMBLE *.  */
#define RELOC_INFO(ptr, offset) \
  ((scm_debug_info *) ((SCM_STACKITEM *) (ptr) + (offset)))
#define RELOC_FRAME(ptr, offset) \
  ((scm_debug_frame *) ((SCM_STACKITEM *) (ptr) + (offset)))


/* Count number of debug info frames on a stack, beginning with
 * DFRAME.  OFFSET is used for relocation of pointers when the stack
 * is read from a continuation.
 */
static int stack_depth SCM_P ((scm_debug_frame *dframe, long offset, SCM *id, int *maxp));
static int
stack_depth (dframe, offset, id, maxp)
     scm_debug_frame *dframe;
     long offset;
     SCM *id;
     int *maxp;
{
  int n, size;
  int max_depth = SCM_BACKTRACE_MAXDEPTH;
  scm_debug_info *info;
  for (n = 0;
       dframe && !SCM_VOIDFRAMEP (*dframe) && n < max_depth;
       dframe = RELOC_FRAME (dframe->prev, offset))
    {
      if (SCM_EVALFRAMEP (*dframe))
        {
          size = dframe->status & SCM_MAX_FRAME_SIZE;
          info = RELOC_INFO (dframe->info, offset);
          n += (info - dframe->vect) / 2 + 1;
          /* Data in the apply part of an eval info frame comes from previous
             stack frame if the scm_debug_info vector is overflowed. */
          if ((((info - dframe->vect) & 1) == 0)
              && SCM_OVERFLOWP (*dframe)
              && !SCM_UNBNDP (info[1].a.proc))
            ++n;
        }
      else
        ++n;
    }
  if (dframe && SCM_VOIDFRAMEP (*dframe))
    *id = dframe->vect[0].id;
  else if (dframe)
    *maxp = 1;
  return n;
}

/* Read debug info from DFRAME into IFRAME.
 */
static void read_frame SCM_P ((scm_debug_frame *dframe, long offset, scm_info_frame *iframe));
static void
read_frame (dframe, offset, iframe)
     scm_debug_frame *dframe;
     long offset;
     scm_info_frame *iframe;
{
  SCM flags = SCM_INUM0;
  int size;
  scm_debug_info *info;
  if (SCM_EVALFRAMEP (*dframe))
    {
      size = dframe->status & SCM_MAX_FRAME_SIZE;
      info = RELOC_INFO (dframe->info, offset);
      if ((info - dframe->vect) & 1)
        {
          /* Debug.vect ends with apply info. */
          --info;
          if (info[1].a.proc != SCM_UNDEFINED)
            {
              flags |= SCM_FRAMEF_PROC;
              iframe->proc = info[1].a.proc;
              iframe->args = info[1].a.args;
              if (!SCM_ARGS_READY_P (*dframe))
                flags |= SCM_FRAMEF_EVAL_ARGS;
            }
        }
      iframe->source = scm_make_memoized (info[0].e.exp, info[0].e.env);
    }
  else
    {
      flags |= SCM_FRAMEF_PROC;
      iframe->proc = dframe->vect[0].a.proc;
      iframe->args = dframe->vect[0].a.args;
    }
  iframe->flags = flags;
}

SCM_SYMBOL (scm_sym_apply, "apply");

/* Look up the first body form of the apply closure.  We'll use this
   below to prevent it from being displayed.
*/
static SCM
get_applybody ()
{
  SCM proc = SCM_CDR (scm_sym2vcell (scm_sym_apply, SCM_BOOL_F, SCM_BOOL_F));
  if (SCM_NIMP (proc) && SCM_CLOSUREP (proc))
    return SCM_CADR (SCM_CODE (proc));
  else
    return SCM_UNDEFINED;
}

#define NEXT_FRAME(iframe, n, quit) \
{ \
  if (SCM_NIMP (iframe->source) \
      && SCM_MEMOIZED_EXP (iframe->source) == applybody) \
    { \
      iframe->source = SCM_BOOL_F; \
      if (SCM_FALSEP (iframe->proc)) \
        { \
          --iframe; \
          ++n; \
        } \
    } \
  ++iframe; \
  if (--n == 0) \
    goto quit; \
} \


/* Fill the scm_info_frame vector IFRAME with data from N stack frames
 * starting with the first stack frame represented by debug frame
 * DFRAME.
 */

static int read_frames SCM_P ((scm_debug_frame *dframe, long offset, int nframes, scm_info_frame *iframes));
static int
read_frames (dframe, offset, n, iframes)
     scm_debug_frame *dframe;
     long offset;
     int n;
     scm_info_frame *iframes;
{
  int size;
  scm_info_frame *iframe = iframes;
  scm_debug_info *info;
  static SCM applybody = SCM_UNDEFINED;
  
  /* The value of applybody has to be setup after r4rs.scm has executed. */
  if (SCM_UNBNDP (applybody))
    applybody = get_applybody ();
  for (;
       dframe && !SCM_VOIDFRAMEP (*dframe) && n > 0;
       dframe = RELOC_FRAME (dframe->prev, offset))
    {
      read_frame (dframe, offset, iframe);
      if (SCM_EVALFRAMEP (*dframe))
        {
          /* If current frame is a macro during expansion, we should
             skip the previously recorded macro transformer
             application frame.  */
          if (SCM_MACROEXPP (*dframe) && iframe > iframes)
            {
              *(iframe - 1) = *iframe;
              --iframe;
            }
          size = dframe->status & SCM_MAX_FRAME_SIZE;
          info =  RELOC_INFO (dframe->info, offset);
          if ((info - dframe->vect) & 1)
            --info;
          /* Data in the apply part of an eval info frame comes from
             previous stack frame if the scm_debug_info vector is overflowed. */
          else if (SCM_OVERFLOWP (*dframe)
                   && !SCM_UNBNDP (info[1].a.proc))
            {
              NEXT_FRAME (iframe, n, quit);
              iframe->flags = SCM_INUM0 | SCM_FRAMEF_PROC;
              iframe->proc = info[1].a.proc;
              iframe->args = info[1].a.args;
            }
          if (SCM_OVERFLOWP (*dframe))
            iframe->flags |= SCM_FRAMEF_OVERFLOW;
          info -= 2;
          NEXT_FRAME (iframe, n, quit);
          while (info >= dframe->vect)
            {
              if (!SCM_UNBNDP (info[1].a.proc))
                {
                  iframe->flags = SCM_INUM0 | SCM_FRAMEF_PROC;
                  iframe->proc = info[1].a.proc;
                  iframe->args = info[1].a.args;
                }
              else
                iframe->flags = SCM_INUM0;
              iframe->source = scm_make_memoized (info[0].e.exp,
                                                  info[0].e.env);
              info -= 2;
              NEXT_FRAME (iframe, n, quit);
            }
        }
      else if (iframe->proc == scm_f_gsubr_apply)
        /* Skip gsubr apply frames. */
        continue;
      else
        {
          NEXT_FRAME (iframe, n, quit);
        }
    quit:
      if (iframe > iframes)
        (iframe - 1) -> flags |= SCM_FRAMEF_REAL;
    }
  return iframe - iframes;  /* Number of frames actually read */
}

static void narrow_stack SCM_P ((SCM stack, int inner, SCM inner_key, int outer, SCM outer_key));

/* Narrow STACK by cutting away stackframes (mutatingly).
 *
 * Inner frames (most recent) are cut by advancing the frames pointer.
 * Outer frames are cut by decreasing the recorded length.
 *
 * Cut maximally INNER inner frames and OUTER outer frames using
 * the keys INNER_KEY and OUTER_KEY.
 *
 * Frames are cut away starting at the end points and moving towards
 * the center of the stack.  The key is normally compared to the
 * operator in application frames.  Frames up to and including the key
 * are cut.
 *
 * If INNER_KEY is #t a different scheme is used for inner frames:
 *
 * Frames up to but excluding the first source frame originating from
 * a user module are cut, except for possible application frames
 * between the user frame and the last system frame previously
 * encountered.
 */

static void
narrow_stack (stack, inner, inner_key, outer, outer_key)
     SCM stack;
     int inner;
     SCM inner_key;
     int outer;
     SCM outer_key;
{
  scm_stack *s = SCM_STACK (stack);
  int i;
  int n = s->length;
  
  /* Cut inner part. */
  if (inner_key == SCM_BOOL_T)
    /* Cut all frames up to user module code */
    {
      for (i = 0; inner; ++i, --inner)
        {
          SCM m = s->frames[i].source;
          if (SCM_NIMP (m)
              && SCM_MEMOIZEDP (m)
              && SCM_NIMP (SCM_MEMOIZED_ENV (m))
              && SCM_FALSEP (scm_system_module_env_p (SCM_MEMOIZED_ENV (m))))
            {
              /* Back up in order to include any non-source frames */
              while (i > 0
                     && !((SCM_NIMP (m = s->frames[i - 1].source)
                           && SCM_MEMOIZEDP (m))
                          || (SCM_NIMP (m = s->frames[i - 1].proc)
                              && SCM_NFALSEP (scm_procedure_p (m))
                              && SCM_NFALSEP (scm_procedure_property
                                              (m, scm_sym_system_procedure)))))
                {
                  --i;
                  ++inner;
                }
              break;
            }
        }
    }
  else
    /* Use standard cutting procedure. */
    {
      for (i = 0; inner; --inner)
        if (s->frames[i++].proc == inner_key)
          break;
    }
  s->frames = &s->frames[i];
  n -= i;

  /* Cut outer part. */
  for (; n && outer; --outer)
    if (s->frames[--n].proc == outer_key)
      break;

  s->length = n;
}

\f

/* Stacks
 */

SCM scm_stack_type;

SCM_PROC (s_stack_p, "stack?", 1, 0, 0, scm_stack_p);
SCM
scm_stack_p (obj)
     SCM obj;
{
  return SCM_NIMP (obj) && SCM_STACKP (obj) ? SCM_BOOL_T : SCM_BOOL_F;
}

SCM_PROC (s_make_stack, "make-stack", 0, 0, 1, scm_make_stack);
SCM
scm_make_stack (args)
     SCM args;
{
  int n, maxp, size;
  scm_debug_frame *dframe;
  scm_info_frame *iframe;
  long offset = 0;
  SCM stack, id;
  SCM obj, inner_cut, outer_cut;

  SCM_ASSERT (SCM_NIMP (args) && SCM_CONSP (args),
              scm_makfrom0str (s_make_stack),
              SCM_WNA,
              NULL);
  obj = SCM_CAR (args);
  args = SCM_CDR (args);

  /* Extract a pointer to the innermost frame of whatever object
     scm_make_stack was given.  */
  if (obj == SCM_BOOL_T)
    dframe = scm_last_debug_frame;
  else
    {
      SCM_ASSERT (SCM_NIMP (obj), obj, SCM_ARG1, s_make_stack);
      if (SCM_DEBUGOBJP (obj))
        dframe = (scm_debug_frame *) SCM_DEBUGOBJ_FRAME (obj);
      else if (scm_tc7_contin == SCM_TYP7 (obj))
        {
          offset = ((SCM_STACKITEM *) (SCM_CHARS (obj) + sizeof (scm_contregs))
                    - SCM_BASE (obj));
#ifndef STACK_GROWS_UP
          offset += SCM_LENGTH (obj);
#endif
          dframe = RELOC_FRAME (SCM_DFRAME (obj), offset);
        }
      else
        {
          scm_wta (obj, (char *) SCM_ARG1, s_make_stack);
          abort ();
        }
    }

  /* Count number of frames.  Also get stack id tag and check whether
     there are more stackframes than we want to record
     (SCM_BACKTRACE_MAXDEPTH). */
  id = SCM_BOOL_F;
  maxp = 0;
  n = stack_depth (dframe, offset, &id, &maxp);
  size = n * SCM_FRAME_N_SLOTS;

  /* Make the stack object. */
  stack = scm_make_struct (scm_stack_type, SCM_MAKINUM (size), SCM_EOL);
  SCM_STACK (stack) -> id = id;
  iframe = &SCM_STACK (stack) -> tail[0];
  SCM_STACK (stack) -> frames = iframe;

  /* Translate the current chain of stack frames into debugging information. */
  n = read_frames (RELOC_FRAME (dframe, offset), offset, n, iframe);
  SCM_STACK (stack) -> length = n;

  /* Narrow the stack according to the arguments given to scm_make_stack. */
  while (n > 0 && SCM_NIMP (args) && SCM_CONSP (args))
    {
      inner_cut = SCM_CAR (args);
      args = SCM_CDR (args);
      if (SCM_NIMP (args) && SCM_CONSP (args))
        {
          outer_cut = SCM_CAR (args);
          args = SCM_CDR (args);
        }
      else
        outer_cut = SCM_INUM0;
      
      narrow_stack (stack,
                    SCM_INUMP (inner_cut) ? SCM_INUM (inner_cut) : n,
                    SCM_INUMP (inner_cut) ? 0 : inner_cut,
                    SCM_INUMP (outer_cut) ? SCM_INUM (outer_cut) : n,
                    SCM_INUMP (outer_cut) ? 0 : outer_cut);

      n = SCM_STACK (stack) -> length;
    }
  
  if (n > 0)
    {
      if (maxp)
        iframe[n - 1].flags |= SCM_FRAMEF_OVERFLOW;
      return stack;
    }
  else
    return SCM_BOOL_F;
}

SCM_PROC (s_stack_id, "stack-id", 1, 0, 0, scm_stack_id);
SCM
scm_stack_id (stack)
     SCM stack;
{
  scm_debug_frame *dframe;
  long offset = 0;
  if (stack == SCM_BOOL_T)
    dframe = scm_last_debug_frame;
  else
    {
      SCM_ASSERT (SCM_NIMP (stack), stack, SCM_ARG1, s_make_stack);
      if (SCM_DEBUGOBJP (stack))
        dframe = (scm_debug_frame *) SCM_DEBUGOBJ_FRAME (stack);
      else if (scm_tc7_contin == SCM_TYP7 (stack))
        {
          offset = ((SCM_STACKITEM *) (SCM_CHARS (stack) + sizeof (scm_contregs))
                    - SCM_BASE (stack));
#ifndef STACK_GROWS_UP
          offset += SCM_LENGTH (stack);
#endif
          dframe = RELOC_FRAME (SCM_DFRAME (stack), offset);
        }
      else if (SCM_STACKP (stack))
        return SCM_STACK (stack) -> id;
      else
        scm_wrong_type_arg (s_stack_id, SCM_ARG1, stack);
    }
  while (dframe && !SCM_VOIDFRAMEP (*dframe))
    dframe = RELOC_FRAME (dframe->prev, offset);
  if (dframe && SCM_VOIDFRAMEP (*dframe))
    return dframe->vect[0].id;
  return SCM_BOOL_F;
}

SCM_PROC (s_stack_ref, "stack-ref", 2, 0, 0, scm_stack_ref);
SCM
scm_stack_ref (stack, i)
     SCM stack;
     SCM i;
{
  SCM_ASSERT (SCM_NIMP (stack)
              && SCM_STACKP (stack),
              stack,
              SCM_ARG1,
              s_stack_ref);
  SCM_ASSERT (SCM_INUMP (i), i, SCM_ARG2, s_stack_ref);
  SCM_ASSERT (SCM_INUM (i) >= 0
              && SCM_INUM (i) < SCM_STACK_LENGTH (stack),
              i,
              SCM_OUTOFRANGE,
              s_stack_ref);
  return scm_cons (stack, i);
}

SCM_PROC(s_stack_length, "stack-length", 1, 0, 0, scm_stack_length);
SCM
scm_stack_length (stack)
     SCM stack;
{
  SCM_ASSERT (SCM_NIMP (stack)
              && SCM_STACKP (stack),
              stack,
              SCM_ARG1,
              s_stack_length);
  return SCM_MAKINUM (SCM_STACK_LENGTH (stack));
}

/* Frames
 */

SCM_PROC (s_frame_p, "frame?", 1, 0, 0, scm_frame_p);
SCM
scm_frame_p (obj)
     SCM obj;
{
  return SCM_NIMP (obj) && SCM_FRAMEP (obj);
}

SCM_PROC(s_last_stack_frame, "last-stack-frame", 1, 0, 0, scm_last_stack_frame);
SCM
scm_last_stack_frame (obj)
     SCM obj;
{
  scm_debug_frame *dframe;
  long offset = 0;
  SCM stack;
  
  SCM_ASSERT (SCM_NIMP (obj), obj, SCM_ARG1, s_last_stack_frame);
  if (SCM_DEBUGOBJP (obj))
    dframe = (scm_debug_frame *) SCM_DEBUGOBJ_FRAME (obj);
  else if (scm_tc7_contin == SCM_TYP7 (obj))
    {
      offset = ((SCM_STACKITEM *) (SCM_CHARS (obj) + sizeof (scm_contregs))
                - SCM_BASE (obj));
#ifndef STACK_GROWS_UP
      offset += SCM_LENGTH (obj);
#endif
      dframe = RELOC_FRAME (SCM_DFRAME (obj), offset);
    }
  else
    {
      scm_wta (obj, (char *) SCM_ARG1, s_last_stack_frame);
      abort ();
    }
  
  if (!dframe || SCM_VOIDFRAMEP (*dframe))
    return SCM_BOOL_F;

  stack = scm_make_struct (scm_stack_type, SCM_MAKINUM (SCM_FRAME_N_SLOTS),
                           SCM_EOL);
  SCM_STACK (stack) -> length = 1;
  SCM_STACK (stack) -> frames = &SCM_STACK (stack) -> tail[0];
  read_frame (dframe, offset,
              (scm_info_frame *) &SCM_STACK (stack) -> frames[0]);
  
  return scm_cons (stack, SCM_INUM0);;
}

SCM_PROC(s_frame_number, "frame-number", 1, 0, 0, scm_frame_number);
SCM
scm_frame_number (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_number);
  return SCM_MAKINUM (SCM_FRAME_NUMBER (frame));
}

SCM_PROC(s_frame_source, "frame-source", 1, 0, 0, scm_frame_source);
SCM
scm_frame_source (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_source);
  return SCM_FRAME_SOURCE (frame);
}

SCM_PROC(s_frame_procedure, "frame-procedure", 1, 0, 0, scm_frame_procedure);
SCM
scm_frame_procedure (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_procedure);
  return (SCM_FRAME_PROC_P (frame)
          ? SCM_FRAME_PROC (frame)
          : SCM_BOOL_F);
}

SCM_PROC(s_frame_arguments, "frame-arguments", 1, 0, 0, scm_frame_arguments);
SCM
scm_frame_arguments (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_arguments);
  return SCM_FRAME_ARGS (frame);
}

SCM_PROC(s_frame_previous, "frame-previous", 1, 0, 0, scm_frame_previous);
SCM
scm_frame_previous (frame)
     SCM frame;
{
  int n;
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_previous);
  n = SCM_INUM (SCM_CDR (frame)) + 1;
  if (n >= SCM_STACK_LENGTH (SCM_CAR (frame)))
    return SCM_BOOL_F;
  else
    return scm_cons (SCM_CAR (frame), SCM_MAKINUM (n));
}

SCM_PROC(s_frame_next, "frame-next", 1, 0, 0, scm_frame_next);
SCM
scm_frame_next (frame)
     SCM frame;
{
  int n;
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_next);
  n = SCM_INUM (SCM_CDR (frame)) - 1;
  if (n < 0)
    return SCM_BOOL_F;
  else
    return scm_cons (SCM_CAR (frame), SCM_MAKINUM (n));
}

SCM_PROC(s_frame_real_p, "frame-real?", 1, 0, 0, scm_frame_real_p);
SCM
scm_frame_real_p (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_real_p);
  return SCM_FRAME_REAL_P (frame) ? SCM_BOOL_T : SCM_BOOL_F;
}

SCM_PROC(s_frame_procedure_p, "frame-procedure?", 1, 0, 0, scm_frame_procedure_p);
SCM
scm_frame_procedure_p (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_procedure_p);
  return SCM_FRAME_PROC_P (frame) ? SCM_BOOL_T : SCM_BOOL_F;
}

SCM_PROC(s_frame_evaluating_args_p, "frame-evaluating-args?", 1, 0, 0, scm_frame_evaluating_args_p);
SCM
scm_frame_evaluating_args_p (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_evaluating_args_p);
  return SCM_FRAME_EVAL_ARGS_P (frame) ? SCM_BOOL_T : SCM_BOOL_F;
}

SCM_PROC(s_frame_overflow_p, "frame-overflow?", 1, 0, 0, scm_frame_overflow_p);
SCM
scm_frame_overflow_p (frame)
     SCM frame;
{
  SCM_ASSERT (SCM_NIMP (frame) && SCM_FRAMEP (frame),
              frame,
              SCM_ARG1,
              s_frame_overflow_p);
  return SCM_FRAME_OVERFLOW_P (frame) ? SCM_BOOL_T : SCM_BOOL_F;
}

\f

void
scm_init_stacks ()
{
  SCM vtable;
  SCM vtable_layout = scm_make_struct_layout (scm_nullstr);
  SCM stack_layout
    = scm_make_struct_layout (scm_makfrom0str (SCM_STACK_LAYOUT));
  vtable = scm_make_vtable_vtable (vtable_layout, SCM_INUM0, SCM_EOL);
  scm_stack_type
    = scm_permanent_object (scm_make_struct (vtable, SCM_INUM0,
                                             scm_cons (stack_layout,
                                                       SCM_EOL)));
#include "stacks.x"
}