* print.c (scm_iprin1): Handle fractions.

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

/* Copyright (C) 1995-1999,2000,2001, 2002, 2003 Free Software Foundation, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */


\f

#include <errno.h>

#include "libguile/_scm.h"
#include "libguile/chars.h"
#include "libguile/continuations.h"
#include "libguile/smob.h"
#include "libguile/eval.h"
#include "libguile/macros.h"
#include "libguile/procprop.h"
#include "libguile/read.h"
#include "libguile/weaks.h"
#include "libguile/unif.h"
#include "libguile/alist.h"
#include "libguile/struct.h"
#include "libguile/objects.h"
#include "libguile/ports.h"
#include "libguile/root.h"
#include "libguile/strings.h"
#include "libguile/strports.h"
#include "libguile/vectors.h"
#include "libguile/lang.h"

#include "libguile/validate.h"
#include "libguile/print.h"
\f

/* {Names of immediate symbols}
 * 
 * This table must agree with the declarations in scm.h: {Immediate Symbols}.
 */

/* This table must agree with the list of flags in tags.h.  */
static const char *iflagnames[] =
{
  "#f",
  "#t",
  "#<undefined>",
  "#<eof>",
  "()",
  "#<unspecified>",

  /* Unbound slot marker for GOOPS.  For internal use in GOOPS only.  */
  "#<unbound>",

  /* Elisp nil value.  This is its Scheme name; whenever it's printed in
   * Elisp, it should appear as the symbol `nil'.  */
  "#nil"
};

/* This table must agree with the list of SCM_IM_ constants in tags.h */
char *scm_isymnames[] =
{
  /* Short instructions */

  "#@and",
  "#@begin",
  "#@case",
  "#@cond",
  "#@do",
  "#@if",
  "#@lambda",
  "#@let",
  "#@let*",
  "#@letrec",
  "#@or",
  "#@quote",
  "#@set!",


  /* Long instructions */

  "#@define",
  "#@apply",
  "#@call-with-current-continuation",
  "#@dispatch",
  "#@slot-ref",
  "#@slot-set!",
  "#@delay",
  "#@future",
  "#@call-with-values",
  "#@else",
  "#@arrow",

  /* Multi-language support */
  "#@nil-cond",
  "#@bind"
};

scm_t_option scm_print_opts[] = {
  { SCM_OPTION_SCM, "closure-hook", SCM_UNPACK (SCM_BOOL_F),
    "Hook for printing closures (should handle macros as well)." },
  { SCM_OPTION_BOOLEAN, "source", 0,
    "Print closures with source." }
};

SCM_DEFINE (scm_print_options, "print-options-interface", 0, 1, 0, 
            (SCM setting),
            "Option interface for the print options. Instead of using\n"
            "this procedure directly, use the procedures\n"
            "@code{print-enable}, @code{print-disable}, @code{print-set!}\n"
            "and @code{print-options}.")
#define FUNC_NAME s_scm_print_options
{
  SCM ans = scm_options (setting,
                         scm_print_opts,
                         SCM_N_PRINT_OPTIONS,
                         FUNC_NAME);
  return ans;
}
#undef FUNC_NAME

\f
/* {Printing of Scheme Objects}
 */

/* Detection of circular references.
 *
 * Due to other constraints in the implementation, this code has bad
 * time complexity (O (depth * N)), The printer code can be
 * rewritten to be O(N).
 */
#define PUSH_REF(pstate, obj) \
do { \
  pstate->ref_stack[pstate->top++] = (obj); \
  if (pstate->top == pstate->ceiling) \
    grow_ref_stack (pstate); \
} while(0)

#define ENTER_NESTED_DATA(pstate, obj, label) \
do { \
  register unsigned long i; \
  for (i = 0; i < pstate->top; ++i) \
    if (SCM_EQ_P (pstate->ref_stack[i], (obj))) \
      goto label; \
  if (pstate->fancyp) \
    { \
      if (pstate->top - pstate->list_offset >= pstate->level) \
        { \
          scm_putc ('#', port); \
          return; \
        } \
    } \
  PUSH_REF(pstate, obj); \
} while(0)

#define EXIT_NESTED_DATA(pstate) { --pstate->top; }

SCM scm_print_state_vtable = SCM_BOOL_F;
static SCM print_state_pool = SCM_EOL;
SCM_MUTEX (print_state_mutex);

#ifdef GUILE_DEBUG /* Used for debugging purposes */

SCM_DEFINE (scm_current_pstate, "current-pstate", 0, 0, 0, 
           (),
            "Return the current-pstate -- the car of the\n"
            "@code{print_state_pool}.  @code{current-pstate} is only\n"
            "included in @code{--enable-guile-debug} builds.")
#define FUNC_NAME s_scm_current_pstate
{
  if (!SCM_NULLP (print_state_pool))
    return SCM_CAR (print_state_pool);
  else
    return SCM_BOOL_F;
}
#undef FUNC_NAME

#endif

#define PSTATE_SIZE 50L

static SCM
make_print_state (void)
{
  SCM print_state
    = scm_make_struct (scm_print_state_vtable, SCM_INUM0, SCM_EOL);
  scm_print_state *pstate = SCM_PRINT_STATE (print_state);
  pstate->ref_vect = scm_c_make_vector (PSTATE_SIZE, SCM_UNDEFINED);
  pstate->ref_stack = SCM_WRITABLE_VELTS (pstate->ref_vect);
  pstate->ceiling = SCM_VECTOR_LENGTH (pstate->ref_vect);
  return print_state;
}

SCM
scm_make_print_state ()
{
  SCM answer = SCM_BOOL_F;

  /* First try to allocate a print state from the pool */
  scm_i_plugin_mutex_lock (&print_state_mutex);
  if (!SCM_NULLP (print_state_pool))
    {
      answer = SCM_CAR (print_state_pool);
      print_state_pool = SCM_CDR (print_state_pool);
    }
  scm_i_plugin_mutex_unlock (&print_state_mutex);
  
  return SCM_FALSEP (answer) ? make_print_state () : answer;
}

void
scm_free_print_state (SCM print_state)
{
  SCM handle;
  scm_print_state *pstate = SCM_PRINT_STATE (print_state);
  /* Cleanup before returning print state to pool.
   * It is better to do it here.  Doing it in scm_prin1
   * would cost more since that function is called much more
   * often.
   */
  pstate->fancyp = 0;
  pstate->revealed = 0;
  scm_i_plugin_mutex_lock (&print_state_mutex);
  handle = scm_cons (print_state, print_state_pool);
  print_state_pool = handle;
  scm_i_plugin_mutex_unlock (&print_state_mutex);
}

SCM
scm_i_port_with_print_state (SCM port, SCM print_state)
{
  if (SCM_UNBNDP (print_state))
    {
      if (SCM_PORT_WITH_PS_P (port))
        return port;
      else
        print_state = scm_make_print_state ();
      /* port does not need to be coerced since it doesn't have ps */
    }
  else
    port = SCM_COERCE_OUTPORT (port);
  SCM_RETURN_NEWSMOB (scm_tc16_port_with_ps,
                      SCM_UNPACK (scm_cons (port, print_state)));
}

static void
grow_ref_stack (scm_print_state *pstate)
{
  unsigned long int old_size = SCM_VECTOR_LENGTH (pstate->ref_vect);
  SCM const *old_elts = SCM_VELTS (pstate->ref_vect);
  unsigned long int new_size = 2 * pstate->ceiling;
  SCM new_vect = scm_c_make_vector (new_size, SCM_UNDEFINED);
  unsigned long int i;

  for (i = 0; i != old_size; ++i)
    SCM_VECTOR_SET (new_vect, i, old_elts [i]);

  pstate->ref_vect = new_vect;
  pstate->ref_stack = SCM_WRITABLE_VELTS(new_vect);
  pstate->ceiling = new_size;
}


static void
print_circref (SCM port, scm_print_state *pstate, SCM ref)
{
  register long i;
  long self = pstate->top - 1;
  i = pstate->top - 1;
  if (SCM_CONSP (pstate->ref_stack[i]))
    {
      while (i > 0)
        {
          if (!SCM_CONSP (pstate->ref_stack[i - 1])
              || !SCM_EQ_P (SCM_CDR (pstate->ref_stack[i - 1]), 
                            pstate->ref_stack[i]))
            break;
          --i;
        }
      self = i;
    }
  for (i = pstate->top - 1; 1; --i)
    if (SCM_EQ_P (pstate->ref_stack[i], ref))
      break;
  scm_putc ('#', port);
  scm_intprint (i - self, 10, port);
  scm_putc ('#', port);
}

/* Print the name of a symbol. */

void
scm_print_symbol_name (const char *str, size_t len, SCM port)
{
  /* This points to the first character that has not yet been written to the
   * port. */
  size_t pos = 0;
  /* This points to the character we're currently looking at. */
  size_t end;
  /* If the name contains weird characters, we'll escape them with
   * backslashes and set this flag; it indicates that we should surround the
   * name with "#{" and "}#". */
  int weird = 0;
  /* Backslashes are not sufficient to make a name weird, but if a name is
   * weird because of other characters, backslahes need to be escaped too.
   * The first time we see a backslash, we set maybe_weird, and mw_pos points
   * to the backslash.  Then if the name turns out to be weird, we re-process
   * everything starting from mw_pos. */
  int maybe_weird = 0;
  size_t mw_pos = 0;
  /* If the name is purely numeric, then it's weird as a whole, even though
   * none of the individual characters is weird.  But we won't know this
   * until we reach the end of the name.  This flag describes the part of the
   * name we've looked at so far. */
  int all_digits = 1;

  if (len == 0 || str[0] == '\'' || str[0] == ':' || str[len-1] == ':')
    {
      scm_lfwrite ("#{", 2, port);
      weird = 1;
    }

  for (end = pos; end < len; ++end)
    switch (str[end])
      {
#ifdef BRACKETS_AS_PARENS
      case '[':
      case ']':
#endif
      case '(':
      case ')':
      case '"':
      case ';':
      case '#':
      case SCM_WHITE_SPACES:
      case SCM_LINE_INCREMENTORS:
        all_digits = 0;
      weird_handler:
        if (maybe_weird)
          {
            end = mw_pos;
            maybe_weird = 0;
          }
        if (!weird)
          {
            scm_lfwrite ("#{", 2, port);
            weird = 1;
          }
        if (pos < end)
          scm_lfwrite (str + pos, end - pos, port);
        {
          char buf[2];
          buf[0] = '\\';
          buf[1] = str[end];
          scm_lfwrite (buf, 2, port);
        }
        pos = end + 1;
        break;
      case '\\':
        all_digits = 0;
        if (weird)
          goto weird_handler;
        if (!maybe_weird)
          {
            maybe_weird = 1;
            mw_pos = pos;
          }
        break;
      case '0': case '1': case '2': case '3': case '4':
      case '5': case '6': case '7': case '8': case '9':
        break;
      default:
        all_digits = 0;
        break;
      }
  if (all_digits)
    {
      scm_lfwrite ("#{", 2, port);
      weird = 1;
    }
  if (pos < end)
    scm_lfwrite (str + pos, end - pos, port);
  if (weird)
    scm_lfwrite ("}#", 2, port);
}

/* Print generally.  Handles both write and display according to PSTATE.
 */
SCM_GPROC(s_write, "write", 1, 1, 0, scm_write, g_write);
SCM_GPROC(s_display, "display", 1, 1, 0, scm_display, g_display);

void 
scm_iprin1 (SCM exp, SCM port, scm_print_state *pstate)
{
  switch (SCM_ITAG3 (exp))
    {
    case scm_tc3_closure:
    case scm_tc3_tc7_1:
    case scm_tc3_tc7_2:
      /* These tc3 tags should never occur in an immediate value.  They are
       * only used in cell types of non-immediates, i. e. the value returned
       * by SCM_CELL_TYPE (exp) can use these tags.
       */
      scm_ipruk ("immediate", exp, port);
      break;
    case scm_tc3_int_1:
    case scm_tc3_int_2:
      scm_intprint (SCM_INUM (exp), 10, port);
      break;
    case scm_tc3_imm24:
      if (SCM_CHARP (exp))
        {
          long i = SCM_CHAR (exp);

          if (SCM_WRITINGP (pstate))
            {
              scm_puts ("#\\", port);
              if ((i >= 0) && (i <= ' ') && scm_charnames[i])
                scm_puts (scm_charnames[i], port);
#ifndef EBCDIC
              else if (i == '\177')
                scm_puts (scm_charnames[scm_n_charnames - 1], port);
#endif
              else if (i < 0 || i > '\177')
                scm_intprint (i, 8, port);
              else
                scm_putc (i, port);
            }
          else
            scm_putc (i, port);
        }
      else if (SCM_IFLAGP (exp)
               && ((size_t) SCM_IFLAGNUM (exp) < (sizeof iflagnames / sizeof (char *))))
        {
          scm_puts (iflagnames [SCM_IFLAGNUM (exp)], port);
        }
      else if (SCM_ISYMP (exp)
               && ((size_t) SCM_ISYMNUM (exp) < (sizeof scm_isymnames / sizeof (char *))))
        {
          scm_puts (SCM_ISYMCHARS (exp), port);
        }
      else if (SCM_ILOCP (exp))
        {
          scm_puts ("#@", port);
          scm_intprint ((long) SCM_IFRAME (exp), 10, port);
          scm_putc (SCM_ICDRP (exp) ? '-' : '+', port);
          scm_intprint ((long) SCM_IDIST (exp), 10, port);
        }
      else
        {
          /* unknown immediate value */
          scm_ipruk ("immediate", exp, port);
        }
      break;
    case scm_tc3_cons:
      switch (SCM_TYP7 (exp))
        {
        case scm_tcs_struct:
          {
            ENTER_NESTED_DATA (pstate, exp, circref);
            if (SCM_OBJ_CLASS_FLAGS (exp) & SCM_CLASSF_GOOPS)
              {
                SCM pwps, print = pstate->writingp ? g_write : g_display;
                if (!print)
                  goto print_struct;
                pwps = scm_i_port_with_print_state (port, pstate->handle);
                pstate->revealed = 1;
                scm_call_generic_2 (print, exp, pwps);
              }
            else
              {
              print_struct:
                scm_print_struct (exp, port, pstate);
              }
            EXIT_NESTED_DATA (pstate);
          }
          break;
        case scm_tcs_cons_imcar:
        case scm_tcs_cons_nimcar:
          ENTER_NESTED_DATA (pstate, exp, circref);
          scm_iprlist ("(", exp, ')', port, pstate);
          EXIT_NESTED_DATA (pstate);
          break;
        circref:
          print_circref (port, pstate, exp);
          break;
        case scm_tcs_closures:
          if (SCM_FALSEP (scm_procedure_p (SCM_PRINT_CLOSURE))
              || SCM_FALSEP (scm_printer_apply (SCM_PRINT_CLOSURE,
                                                exp, port, pstate)))
            {
              SCM formals = SCM_CLOSURE_FORMALS (exp);
              scm_puts ("#<procedure", port);
              scm_putc (' ', port);
              scm_iprin1 (scm_procedure_name (exp), port, pstate);
              scm_putc (' ', port);
              if (SCM_PRINT_SOURCE_P)
                {
                  SCM env = SCM_ENV (exp);
                  SCM xenv = SCM_EXTEND_ENV (formals, SCM_EOL, env);
                  SCM src = scm_unmemocopy (SCM_CODE (exp), xenv);
                  ENTER_NESTED_DATA (pstate, exp, circref);
                  scm_iprin1 (src, port, pstate);
                  EXIT_NESTED_DATA (pstate);
                }
              else
                scm_iprin1 (formals, port, pstate);
              scm_putc ('>', port);
            }
          break;
        case scm_tc7_number:
          switch SCM_TYP16 (exp) {
          case scm_tc16_big:
            scm_bigprint (exp, port, pstate);
            break;
          case scm_tc16_real:
            scm_print_real (exp, port, pstate);
            break;
          case scm_tc16_complex:
            scm_print_complex (exp, port, pstate);
            break;
          case scm_tc16_fraction:
            scm_i_print_fraction (exp, port, pstate);
            break;
          }
          break;
        case scm_tc7_string:
          if (SCM_WRITINGP (pstate))
            {
              size_t i;

              scm_putc ('"', port);
              for (i = 0; i < SCM_STRING_LENGTH (exp); ++i)
                switch (SCM_STRING_CHARS (exp)[i])
                  {
                  case '"':
                  case '\\':
                    scm_putc ('\\', port);
                  default:
                    scm_putc (SCM_STRING_CHARS (exp)[i], port);
                  }
              scm_putc ('"', port);
              break;
            }
          else
            scm_lfwrite (SCM_STRING_CHARS (exp), SCM_STRING_LENGTH (exp), port);
          break;
        case scm_tc7_symbol:
          if (SCM_SYMBOL_INTERNED_P (exp))
            {
              scm_print_symbol_name (SCM_SYMBOL_CHARS (exp),
                                     SCM_SYMBOL_LENGTH (exp),
                                     port);
              scm_remember_upto_here_1 (exp);
            }
          else
            {
              scm_puts ("#<uninterned-symbol ", port);
              scm_print_symbol_name (SCM_SYMBOL_CHARS (exp),
                                     SCM_SYMBOL_LENGTH (exp),
                                     port);
              scm_putc (' ', port);
              scm_intprint ((long)exp, 16, port);
              scm_putc ('>', port);
            }
          break;
        case scm_tc7_variable:
          scm_i_variable_print (exp, port, pstate);
          break;
        case scm_tc7_wvect:
          ENTER_NESTED_DATA (pstate, exp, circref);
          if (SCM_IS_WHVEC (exp))
            scm_puts ("#wh(", port);
          else
            scm_puts ("#w(", port);
          goto common_vector_printer;

        case scm_tc7_vector:
          ENTER_NESTED_DATA (pstate, exp, circref);
          scm_puts ("#(", port);
        common_vector_printer:
          {
            register long i;
            long last = SCM_VECTOR_LENGTH (exp) - 1;
            int cutp = 0;
            if (pstate->fancyp && SCM_VECTOR_LENGTH (exp) > pstate->length)
              {
                last = pstate->length - 1;
                cutp = 1;
              }
            for (i = 0; i < last; ++i)
              {
                /* CHECK_INTS; */
                scm_iprin1 (SCM_VELTS (exp)[i], port, pstate);
                scm_putc (' ', port);
              }
            if (i == last)
              {
                /* CHECK_INTS; */
                scm_iprin1 (SCM_VELTS (exp)[i], port, pstate);
              }
            if (cutp)
              scm_puts (" ...", port);
            scm_putc (')', port);
          }
          EXIT_NESTED_DATA (pstate);
          break;
#if SCM_HAVE_ARRAYS
        case scm_tc7_bvect:
        case scm_tc7_byvect:
        case scm_tc7_svect:
        case scm_tc7_ivect:
        case scm_tc7_uvect:
        case scm_tc7_fvect:
        case scm_tc7_dvect:
        case scm_tc7_cvect:
#if SCM_SIZEOF_LONG_LONG != 0
        case scm_tc7_llvect:
#endif
          scm_raprin1 (exp, port, pstate);
          break;
#endif
        case scm_tcs_subrs:
          scm_puts (SCM_SUBR_GENERIC (exp)
                    ? "#<primitive-generic "
                    : "#<primitive-procedure ",
                    port);
          scm_puts (SCM_SYMBOL_CHARS (SCM_SNAME (exp)), port);
          scm_putc ('>', port);
          break;
#ifdef CCLO
        case scm_tc7_cclo:
          {
            SCM proc = SCM_CCLO_SUBR (exp);
            if (SCM_EQ_P (proc, scm_f_gsubr_apply))
              {
                /* Print gsubrs as primitives */
                SCM name = scm_procedure_name (exp);
                scm_puts ("#<primitive-procedure", port);
                if (!SCM_FALSEP (name))
                  {
                    scm_putc (' ', port);
                    scm_puts (SCM_SYMBOL_CHARS (name), port);
                  }
              }
            else
              {
                scm_puts ("#<compiled-closure ", port);
                scm_iprin1 (proc, port, pstate);
              }
            scm_putc ('>', port);
          }
          break;
#endif
        case scm_tc7_pws:
          scm_puts ("#<procedure-with-setter", port);
          {
            SCM name = scm_procedure_name (exp);
            if (!SCM_FALSEP (name))
              {
                scm_putc (' ', port);
                scm_display (name, port);
              }
          }
          scm_putc ('>', port);
          break;
        case scm_tc7_port:
          {
            register long i = SCM_PTOBNUM (exp);
            if (i < scm_numptob
                && scm_ptobs[i].print
                && (scm_ptobs[i].print) (exp, port, pstate))
              break;
            goto punk;
          }
        case scm_tc7_smob:
          ENTER_NESTED_DATA (pstate, exp, circref);
          SCM_SMOB_DESCRIPTOR (exp).print (exp, port, pstate);
          EXIT_NESTED_DATA (pstate);
          break;
        default:
        punk:
          scm_ipruk ("type", exp, port);
        }
    }
}

/* Print states are necessary for circular reference safe printing.
 * They are also expensive to allocate.  Therefore print states are
 * kept in a pool so that they can be reused.
 */

/* The PORT argument can also be a print-state/port pair, which will
 * then be used instead of allocating a new print state.  This is
 * useful for continuing a chain of print calls from Scheme.  */

void 
scm_prin1 (SCM exp, SCM port, int writingp)
{
  SCM handle = SCM_BOOL_F; /* Will GC protect the handle whilst unlinked */
  SCM pstate_scm;
  scm_print_state *pstate;
  int old_writingp;

  /* If PORT is a print-state/port pair, use that.  Else create a new
     print-state. */

  if (SCM_PORT_WITH_PS_P (port))
    {
      pstate_scm = SCM_PORT_WITH_PS_PS (port);
      port = SCM_PORT_WITH_PS_PORT (port);
    }
  else
    {
      /* First try to allocate a print state from the pool */
      scm_i_plugin_mutex_lock (&print_state_mutex);
      if (!SCM_NULLP (print_state_pool))
        {
          handle = print_state_pool;
          print_state_pool = SCM_CDR (print_state_pool);
        }
      scm_i_plugin_mutex_unlock (&print_state_mutex);
      if (SCM_FALSEP (handle))
        handle = scm_list_1 (make_print_state ());
      pstate_scm = SCM_CAR (handle);
    }

  pstate = SCM_PRINT_STATE (pstate_scm);
  old_writingp = pstate->writingp;
  pstate->writingp = writingp;
  scm_iprin1 (exp, port, pstate);
  pstate->writingp = old_writingp;

  /* Return print state to pool if it has been created above and
     hasn't escaped to Scheme. */

  if (!SCM_FALSEP (handle) && !pstate->revealed)
    {
      scm_i_plugin_mutex_lock (&print_state_mutex);
      SCM_SETCDR (handle, print_state_pool);
      print_state_pool = handle;
      scm_i_plugin_mutex_unlock (&print_state_mutex);
    }
}


/* Print an integer.
 */

void 
scm_intprint (long n, int radix, SCM port)
{
  char num_buf[SCM_INTBUFLEN];
  scm_lfwrite (num_buf, scm_iint2str (n, radix, num_buf), port);
}

/* Print an object of unrecognized type.
 */

void 
scm_ipruk (char *hdr, SCM ptr, SCM port)
{
  scm_puts ("#<unknown-", port);
  scm_puts (hdr, port);
  if (scm_in_heap_p (ptr))
    {
      scm_puts (" (0x", port);
      scm_intprint (SCM_CELL_WORD_0 (ptr), 16, port);
      scm_puts (" . 0x", port);
      scm_intprint (SCM_CELL_WORD_1 (ptr), 16, port);
      scm_puts (") @", port);
    }
  scm_puts (" 0x", port);
  scm_intprint (SCM_UNPACK (ptr), 16, port);
  scm_putc ('>', port);
}


/* Print a list.
 */
void 
scm_iprlist (char *hdr, SCM exp, int tlr, SCM port, scm_print_state *pstate)
{
  register SCM hare, tortoise;
  long floor = pstate->top - 2;
  scm_puts (hdr, port);
  /* CHECK_INTS; */
  if (pstate->fancyp)
    goto fancy_printing;
  
  /* Run a hare and tortoise so that total time complexity will be
     O(depth * N) instead of O(N^2). */
  hare = SCM_CDR (exp);
  tortoise = exp;
  while (SCM_CONSP (hare))
    {
      if (SCM_EQ_P (hare, tortoise))
        goto fancy_printing;
      hare = SCM_CDR (hare);
      if (!SCM_CONSP (hare))
        break;
      hare = SCM_CDR (hare);
      tortoise = SCM_CDR (tortoise);
    }
  
  /* No cdr cycles intrinsic to this list */
  scm_iprin1 (SCM_CAR (exp), port, pstate);
  for (exp = SCM_CDR (exp); SCM_CONSP (exp); exp = SCM_CDR (exp))
    {
      register long i;

      for (i = floor; i >= 0; --i)
        if (SCM_EQ_P (pstate->ref_stack[i], exp))
          goto circref;
      PUSH_REF (pstate, exp);
      scm_putc (' ', port);
      /* CHECK_INTS; */
      scm_iprin1 (SCM_CAR (exp), port, pstate);
    }
  if (!SCM_NULL_OR_NIL_P (exp))
    {
      scm_puts (" . ", port);
      scm_iprin1 (exp, port, pstate);
    }

end:
  scm_putc (tlr, port);
  pstate->top = floor + 2;
  return;
  
fancy_printing:
  {
    long n = pstate->length;
    
    scm_iprin1 (SCM_CAR (exp), port, pstate);
    exp = SCM_CDR (exp); --n;
    for (; SCM_CONSP (exp); exp = SCM_CDR (exp))
      {
        register unsigned long i;

        for (i = 0; i < pstate->top; ++i)
          if (SCM_EQ_P (pstate->ref_stack[i], exp))
            goto fancy_circref;
        if (pstate->fancyp)
          {
            if (n == 0)
              {
                scm_puts (" ...", port);
                goto skip_tail;
              }
            else
              --n;
          }
        PUSH_REF(pstate, exp);
        ++pstate->list_offset;
        scm_putc (' ', port);
        /* CHECK_INTS; */
        scm_iprin1 (SCM_CAR (exp), port, pstate);
      }
  }
  if (!SCM_NULL_OR_NIL_P (exp))
    {
      scm_puts (" . ", port);
      scm_iprin1 (exp, port, pstate);
    }
skip_tail:
  pstate->list_offset -= pstate->top - floor - 2;
  goto end;

fancy_circref:
  pstate->list_offset -= pstate->top - floor - 2;
  
circref:
  scm_puts (" . ", port);
  print_circref (port, pstate, exp);
  goto end;
}

\f

int
scm_valid_oport_value_p (SCM val)
{
  return (SCM_OPOUTPORTP (val)
          || (SCM_PORT_WITH_PS_P (val)
              && SCM_OPOUTPORTP (SCM_PORT_WITH_PS_PORT (val))));
}

/* SCM_GPROC(s_write, "write", 1, 1, 0, scm_write, g_write); */

SCM 
scm_write (SCM obj, SCM port)
{
  if (SCM_UNBNDP (port))
    port = scm_cur_outp;

  SCM_ASSERT (scm_valid_oport_value_p (port), port, SCM_ARG2, s_write);

  scm_prin1 (obj, port, 1);
#ifdef HAVE_PIPE
# ifdef EPIPE
  if (EPIPE == errno)
    scm_close_port (port);
# endif
#endif
  return SCM_UNSPECIFIED;
}


/* SCM_GPROC(s_display, "display", 1, 1, 0, scm_display, g_display); */

SCM 
scm_display (SCM obj, SCM port)
{
  if (SCM_UNBNDP (port))
    port = scm_cur_outp;

  SCM_ASSERT (scm_valid_oport_value_p (port), port, SCM_ARG2, s_display);

  scm_prin1 (obj, port, 0);
#ifdef HAVE_PIPE
# ifdef EPIPE
  if (EPIPE == errno)
    scm_close_port (port);
# endif
#endif
  return SCM_UNSPECIFIED;
}


SCM_DEFINE (scm_simple_format, "simple-format", 2, 0, 1,
            (SCM destination, SCM message, SCM args),
            "Write @var{message} to @var{destination}, defaulting to\n"
            "the current output port.\n"
            "@var{message} can contain @code{~A} (was @code{%s}) and\n"
            "@code{~S} (was @code{%S}) escapes.  When printed,\n"
            "the escapes are replaced with corresponding members of\n"
            "@var{ARGS}:\n"
            "@code{~A} formats using @code{display} and @code{~S} formats\n"
            "using @code{write}.\n"
            "If @var{destination} is @code{#t}, then use the current output\n"
            "port, if @var{destination} is @code{#f}, then return a string\n"
            "containing the formatted text. Does not add a trailing newline.")
#define FUNC_NAME s_scm_simple_format
{
  SCM port, answer = SCM_UNSPECIFIED;
  int fReturnString = 0;
  int writingp;
  char *start;
  char *end;
  char *p;

  if (SCM_EQ_P (destination, SCM_BOOL_T))
    {
      destination = port = scm_cur_outp;
    }
  else if (SCM_FALSEP (destination))
    {
      fReturnString = 1;
      port = scm_mkstrport (SCM_INUM0, 
                            scm_make_string (SCM_INUM0, SCM_UNDEFINED),
                            SCM_OPN | SCM_WRTNG,
                            FUNC_NAME);
      destination = port;
    }
  else
    {
      SCM_VALIDATE_OPORT_VALUE (1, destination);
      port = SCM_COERCE_OUTPORT (destination);
    }
  SCM_VALIDATE_STRING (2, message);
  SCM_VALIDATE_REST_ARGUMENT (args);

  start = SCM_STRING_CHARS (message);
  end = start + SCM_STRING_LENGTH (message);
  for (p = start; p != end; ++p)
    if (*p == '~')
      {
        if (++p == end)
          break;

        switch (*p) 
          {
          case 'A': case 'a':
            writingp = 0;
            break;
          case 'S': case 's':
            writingp = 1;
            break;
          case '~':
            scm_lfwrite (start, p - start, port);
            start = p + 1;
            continue;
          case '%':
            scm_lfwrite (start, p - start - 1, port);
            scm_newline (port);
            start = p + 1;
            continue;
          default:
            SCM_MISC_ERROR ("FORMAT: Unsupported format option ~~~A - use (ice-9 format) instead",
                            scm_list_1 (SCM_MAKE_CHAR (*p)));
            
          }


        if (!SCM_CONSP (args))
          SCM_MISC_ERROR ("FORMAT: Missing argument for ~~~A",
                          scm_list_1 (SCM_MAKE_CHAR (*p)));
                                        
        scm_lfwrite (start, p - start - 1, port);
        /* we pass destination here */
        scm_prin1 (SCM_CAR (args), destination, writingp);
        args = SCM_CDR (args);
        start = p + 1;
      }

  scm_lfwrite (start, p - start, port);
  if (!SCM_EQ_P (args, SCM_EOL))
    SCM_MISC_ERROR ("FORMAT: ~A superfluous arguments",
                    scm_list_1 (scm_length (args)));

  if (fReturnString)
    answer = scm_strport_to_string (destination);

  return scm_return_first (answer, message);
}
#undef FUNC_NAME


SCM_DEFINE (scm_newline, "newline", 0, 1, 0, 
            (SCM port),
            "Send a newline to @var{port}.\n"
            "If @var{port} is omitted, send to the current output port.")
#define FUNC_NAME s_scm_newline
{
  if (SCM_UNBNDP (port))
    port = scm_cur_outp;

  SCM_VALIDATE_OPORT_VALUE (1, port);

  scm_putc ('\n', SCM_COERCE_OUTPORT (port));
  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME

SCM_DEFINE (scm_write_char, "write-char", 1, 1, 0,
            (SCM chr, SCM port),
            "Send character @var{chr} to @var{port}.")
#define FUNC_NAME s_scm_write_char
{
  if (SCM_UNBNDP (port))
    port = scm_cur_outp;

  SCM_VALIDATE_CHAR (1, chr);
  SCM_VALIDATE_OPORT_VALUE (2, port);

  scm_putc ((int) SCM_CHAR (chr), SCM_COERCE_OUTPORT (port));
#ifdef HAVE_PIPE
# ifdef EPIPE
  if (EPIPE == errno)
    scm_close_port (port);
# endif
#endif
  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME

\f

/* Call back to Scheme code to do the printing of special objects
 * (like structs).  SCM_PRINTER_APPLY applies PROC to EXP and a smob
 * containing PORT and PSTATE.  This object can be used as the port for
 * display/write etc to continue the current print chain.  The REVEALED
 * field of PSTATE is set to true to indicate that the print state has
 * escaped to Scheme and thus has to be freed by the GC.
 */

scm_t_bits scm_tc16_port_with_ps;

/* Print exactly as the port itself would */

static int
port_with_ps_print (SCM obj, SCM port, scm_print_state *pstate)
{
  obj = SCM_PORT_WITH_PS_PORT (obj);
  return scm_ptobs[SCM_PTOBNUM (obj)].print (obj, port, pstate);
}

SCM
scm_printer_apply (SCM proc, SCM exp, SCM port, scm_print_state *pstate)
{
  pstate->revealed = 1;
  return scm_call_2 (proc, exp,
                     scm_i_port_with_print_state (port, pstate->handle));
}

SCM_DEFINE (scm_port_with_print_state, "port-with-print-state", 1, 1, 0, 
            (SCM port, SCM pstate),
            "Create a new port which behaves like @var{port}, but with an\n"
            "included print state @var{pstate}.  @var{pstate} is optional.\n"
            "If @var{pstate} isn't supplied and @var{port} already has\n"
            "a print state, the old print state is reused.")
#define FUNC_NAME s_scm_port_with_print_state
{
  SCM_VALIDATE_OPORT_VALUE (1, port);
  if (!SCM_UNBNDP (pstate))
    SCM_VALIDATE_PRINTSTATE (2, pstate);
  return scm_i_port_with_print_state (port, pstate);
}
#undef FUNC_NAME

SCM_DEFINE (scm_get_print_state, "get-print-state", 1, 0, 0, 
            (SCM port),
            "Return the print state of the port @var{port}. If @var{port}\n"
            "has no associated print state, @code{#f} is returned.")
#define FUNC_NAME s_scm_get_print_state
{
  if (SCM_PORT_WITH_PS_P (port))
    return SCM_PORT_WITH_PS_PS (port);
  if (SCM_OUTPUT_PORT_P (port))
    return SCM_BOOL_F;
  SCM_WRONG_TYPE_ARG (1, port);
}
#undef FUNC_NAME

\f

void
scm_init_print ()
{
  SCM vtable, layout, type;

  scm_init_opts (scm_print_options, scm_print_opts, SCM_N_PRINT_OPTIONS);

  scm_gc_register_root (&print_state_pool);
  scm_gc_register_root (&scm_print_state_vtable);
  vtable = scm_make_vtable_vtable (scm_nullstr, SCM_INUM0, SCM_EOL);
  layout = scm_make_struct_layout (scm_makfrom0str (SCM_PRINT_STATE_LAYOUT));
  type = scm_make_struct (vtable, SCM_INUM0, scm_list_1 (layout));
  scm_set_struct_vtable_name_x (type, scm_str2symbol ("print-state"));
  scm_print_state_vtable = type;

  /* Don't want to bind a wrapper class in GOOPS, so pass 0 as arg1. */
  scm_tc16_port_with_ps = scm_make_smob_type (0, 0);
  scm_set_smob_mark (scm_tc16_port_with_ps, scm_markcdr);
  scm_set_smob_print (scm_tc16_port_with_ps, port_with_ps_print);
  
#include "libguile/print.x"
}

/*
  Local Variables:
  c-file-style: "gnu"
  End:
*/