/*
  Racket
  Copyright (c) 2004-2018 PLT Design Inc.
  Copyright (c) 1995-2001 Matthew Flatt

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 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
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301 USA.

  libscheme
  Copyright (c) 1994 Brent Benson
  All rights reserved.
*/

/* Most of this source file is pathname manipulation functions.  At
   the bottom, a path is just a byte string, not necessarily
   normalized in any way, except that it doesn't contain a nul
   character. The advantage of this representation is that it keeps
   paths the way the user wrote them. The tremendous disadvantage of
   this representation is that all of the operations must manipulate
   strings.

   A major complication is the complex syntax of Windows paths. Again,
   since all the operations work on the string, the code in this file
   parses and re-parses constantly.

 */

#include "schpriv.h"
#include "schrktio.h"
#include <ctype.h>

#define UNIX_FN_SEP '/'
#define IS_A_UNIX_SEP(x) ((x) == '/')
#define IS_A_UNIX_PRIM_SEP(x) IS_A_UNIX_SEP(x)

#define DOS_FN_SEP '\\'
#define IS_A_DOS_SEP(x) (((x) == '/') || ((x) == '\\'))
#define IS_A_DOS_PRIM_SEP(x) ((x) == '\\')
#define IS_A_DOS_X_SEP(prim, x) (prim ? IS_A_DOS_PRIM_SEP(x) : IS_A_DOS_SEP(x))

#define FN_SEP(kind) ((kind == SCHEME_UNIX_PATH_KIND) ? UNIX_FN_SEP : DOS_FN_SEP)
#define IS_A_SEP(kind, x) ((kind == SCHEME_UNIX_PATH_KIND) ? IS_A_UNIX_SEP(x) : IS_A_DOS_SEP(x))
#define IS_A_PRIM_SEP(kind, x) ((kind == SCHEME_UNIX_PATH_KIND) ? IS_A_UNIX_PRIM_SEP(x) : IS_A_DOS_PRIM_SEP(x))

#define CURRENT_WD() scheme_get_param(scheme_current_config(), MZCONFIG_CURRENT_DIRECTORY)

#define TO_PATH(x) (SCHEME_GENERAL_PATHP(x) ? x : scheme_char_string_to_path(x))

/* Define TILDE_IS_ABSOLUTE to get pre-v4.0 handling of "~". */

#ifdef TILDE_IS_ABSOLUTE
# define WHEN_TILDE_IS_ABSOLUTE(x) (x)
#else
# define WHEN_TILDE_IS_ABSOLUTE(x) 0
#endif

static int check_dos_slashslash_drive(const char *next, int delta, int len, 
				      int *drive_end, int exact, int no_fw);
static int check_dos_slashslash_qm(const char *next, int len, int *drive_end, 
				   int *clean_start, int *add_sep);

#define is_drive_letter(c) (((unsigned char)c < 128) && isalpha((unsigned char)c))

#ifdef __clang__
# ifdef MZ_PRECISE_GC
#  pragma clang diagnostic ignored "-Wtautological-compare"
# endif
#endif

/* local */
static Scheme_Object *path_p(int argc, Scheme_Object **argv);
static Scheme_Object *general_path_p(int argc, Scheme_Object **argv);
static Scheme_Object *path_to_string(int argc, Scheme_Object **argv);
static Scheme_Object *path_to_bytes(int argc, Scheme_Object **argv);
static Scheme_Object *path_element_to_bytes(int argc, Scheme_Object **argv);
static Scheme_Object *path_element_to_string(int argc, Scheme_Object **argv);
static Scheme_Object *string_to_path(int argc, Scheme_Object **argv);
static Scheme_Object *bytes_to_path(int argc, Scheme_Object **argv);
static Scheme_Object *bytes_to_path_element(int argc, Scheme_Object **argv);
static Scheme_Object *string_to_path_element(int argc, Scheme_Object **argv);
static Scheme_Object *path_kind(int argc, Scheme_Object **argv);
static Scheme_Object *platform_path_kind(int argc, Scheme_Object **argv);

static Scheme_Object *file_exists(int argc, Scheme_Object **argv);
static Scheme_Object *directory_exists(int argc, Scheme_Object **argv);
static Scheme_Object *link_exists(int argc, Scheme_Object **argv);

static Scheme_Object *build_path_kind(int argc, Scheme_Object **argv);
static Scheme_Object *delete_file(int argc, Scheme_Object **argv);
static Scheme_Object *rename_file(int argc, Scheme_Object **argv);
static Scheme_Object *copy_file(int argc, Scheme_Object **argv);
static Scheme_Object *path_to_directory_path(int argc, Scheme_Object *argv[]);
static Scheme_Object *directory_list(int argc, Scheme_Object *argv[]);
static Scheme_Object *filesystem_root_list(int argc, Scheme_Object *argv[]);
static Scheme_Object *make_directory(int argc, Scheme_Object *argv[]);
static Scheme_Object *delete_directory(int argc, Scheme_Object *argv[]);
static Scheme_Object *make_link(int argc, Scheme_Object *argv[]);
static Scheme_Object *split_path(int argc, Scheme_Object **argv);
static Scheme_Object *explode_path(int argc, Scheme_Object **argv);
static Scheme_Object *relative_path_p(int argc, Scheme_Object **argv);
static Scheme_Object *absolute_path_p(int argc, Scheme_Object **argv);
static Scheme_Object *complete_path_p(int argc, Scheme_Object **argv);
static Scheme_Object *path_to_complete_path(int argc, Scheme_Object **argv);
static Scheme_Object *resolve_path(int argc, Scheme_Object *argv[]);
static Scheme_Object *cleanse_path(int argc, Scheme_Object *argv[]);
static Scheme_Object *expand_user_path(int argc, Scheme_Object *argv[]);
static Scheme_Object *current_drive(int argc, Scheme_Object *argv[]);
static Scheme_Object *file_modify_seconds(int argc, Scheme_Object *argv[]);
static Scheme_Object *file_or_dir_permissions(int argc, Scheme_Object *argv[]);
static Scheme_Object *file_identity(int argc, Scheme_Object *argv[]);
static Scheme_Object *file_size(int argc, Scheme_Object *argv[]);
static Scheme_Object *find_system_path(int argc, Scheme_Object **argv);

static Scheme_Object *current_directory(int argc, Scheme_Object *argv[]);
static Scheme_Object *current_user_directory(int argc, Scheme_Object *argv[]);
static Scheme_Object *current_force_delete_perms(int argc, Scheme_Object *argv[]);

static int has_null(const char *s, intptr_t l);
static void raise_null_error(const char *name, Scheme_Object *path, const char *mod);

static char *do_path_to_complete_path(char *filename, intptr_t ilen, const char *wrt, intptr_t wlen, int kind);
static Scheme_Object *do_simplify_path(Scheme_Object *path, Scheme_Object *cycle_check, int skip, int use_filesystem,
				       int force_rel_up, int kind, int guards);
static char *do_normal_path_seps(char *si, int *_len, int delta, int strip_trail, int kind, int *_did);
static char *remove_redundant_slashes(char *filename, int *l, int delta, int *expanded, int kind);
static Scheme_Object *do_path_to_directory_path(char *s, intptr_t offset, intptr_t len, Scheme_Object *p, int just_check, int kind);

READ_ONLY static Scheme_Object *up_symbol;
READ_ONLY static Scheme_Object *relative_symbol;
READ_ONLY static Scheme_Object *same_symbol;
READ_ONLY static Scheme_Object *read_symbol, *write_symbol, *execute_symbol;

READ_ONLY static Scheme_Object *temp_dir_symbol, *home_dir_symbol, *pref_dir_symbol;
READ_ONLY static Scheme_Object *doc_dir_symbol, *desk_dir_symbol;
READ_ONLY static Scheme_Object *init_dir_symbol, *init_file_symbol, *sys_dir_symbol;
READ_ONLY static Scheme_Object *exec_file_symbol, *run_file_symbol, *collects_dir_symbol;
READ_ONLY static Scheme_Object *pref_file_symbol, *orig_dir_symbol, *addon_dir_symbol;
READ_ONLY static Scheme_Object *config_dir_symbol;
READ_ONLY static Scheme_Object *host_collects_dir_symbol, *host_config_dir_symbol;

SHARED_OK static Scheme_Object *exec_cmd;
SHARED_OK static Scheme_Object *run_cmd;
SHARED_OK static Scheme_Object *collects_path, *config_path;
SHARED_OK static Scheme_Object *host_collects_path, *host_config_path;
THREAD_LOCAL_DECL(static Scheme_Object *original_pwd);
SHARED_OK static Scheme_Object *addon_dir;

READ_ONLY static Scheme_Object *windows_symbol, *unix_symbol;

void scheme_init_file(Scheme_Startup_Env *env)
{
  Scheme_Object *p;

  REGISTER_SO(up_symbol);
  REGISTER_SO(relative_symbol);
  REGISTER_SO(same_symbol);
  REGISTER_SO(read_symbol);
  REGISTER_SO(write_symbol);
  REGISTER_SO(execute_symbol);
  
  REGISTER_SO(temp_dir_symbol);
  REGISTER_SO(home_dir_symbol);
  REGISTER_SO(pref_dir_symbol);
  REGISTER_SO(doc_dir_symbol);
  REGISTER_SO(desk_dir_symbol);
  REGISTER_SO(init_dir_symbol);
  REGISTER_SO(init_file_symbol);
  REGISTER_SO(sys_dir_symbol);
  REGISTER_SO(pref_file_symbol);
  REGISTER_SO(exec_file_symbol);
  REGISTER_SO(run_file_symbol);
  REGISTER_SO(collects_dir_symbol);
  REGISTER_SO(config_dir_symbol);
  REGISTER_SO(host_collects_dir_symbol);
  REGISTER_SO(host_config_dir_symbol);
  REGISTER_SO(orig_dir_symbol);
  REGISTER_SO(addon_dir_symbol);

  REGISTER_SO(windows_symbol);
  REGISTER_SO(unix_symbol);

  up_symbol = scheme_intern_symbol("up");
  relative_symbol = scheme_intern_symbol("relative");
  same_symbol = scheme_intern_symbol("same");
  
  read_symbol = scheme_intern_symbol("read");
  write_symbol = scheme_intern_symbol("write");
  execute_symbol = scheme_intern_symbol("execute");
  
  temp_dir_symbol = scheme_intern_symbol("temp-dir");
  home_dir_symbol = scheme_intern_symbol("home-dir");
  doc_dir_symbol = scheme_intern_symbol("doc-dir");
  desk_dir_symbol = scheme_intern_symbol("desk-dir");
  pref_dir_symbol = scheme_intern_symbol("pref-dir");
  init_dir_symbol = scheme_intern_symbol("init-dir");
  init_file_symbol = scheme_intern_symbol("init-file");
  sys_dir_symbol = scheme_intern_symbol("sys-dir");
  pref_file_symbol = scheme_intern_symbol("pref-file");
  exec_file_symbol = scheme_intern_symbol("exec-file");
  run_file_symbol = scheme_intern_symbol("run-file");
  collects_dir_symbol = scheme_intern_symbol("collects-dir");
  config_dir_symbol = scheme_intern_symbol("config-dir");
  host_collects_dir_symbol = scheme_intern_symbol("host-collects-dir");
  host_config_dir_symbol = scheme_intern_symbol("host-config-dir");
  orig_dir_symbol = scheme_intern_symbol("orig-dir");
  addon_dir_symbol = scheme_intern_symbol("addon-dir");

  windows_symbol = scheme_intern_symbol("windows");
  unix_symbol = scheme_intern_symbol("unix");

  p = scheme_make_immed_prim(path_p, "path?", 1, 1);
  SCHEME_PRIM_PROC_FLAGS(p) |= scheme_intern_prim_opt_flags(SCHEME_PRIM_IS_UNARY_INLINED
                                                            | SCHEME_PRIM_IS_OMITABLE
                                                            | SCHEME_PRIM_PRODUCES_BOOL);
  scheme_addto_prim_instance("path?", p, env);

  scheme_addto_prim_instance("path-for-some-system?", 
			     scheme_make_folding_prim(general_path_p, 
                                                      "path-for-some-system?", 
                                                      1, 1, 1), 
			     env);
  scheme_addto_prim_instance("path-convention-type", 
			     scheme_make_folding_prim(path_kind, 
                                                      "path-convention-type", 
                                                      1, 1, 1), 
			     env);
  scheme_addto_prim_instance("system-path-convention-type", 
			     scheme_make_immed_prim(platform_path_kind, 
                                                    "system-path-convention-type", 
                                                    0, 0),
			     env);
  scheme_addto_prim_instance("path->string", 
			     scheme_make_immed_prim(path_to_string, 
                                                    "path->string", 
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("path->bytes", 
			     scheme_make_immed_prim(path_to_bytes, 
                                                    "path->bytes", 
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("path-element->bytes", 
			     scheme_make_immed_prim(path_element_to_bytes, 
                                                    "path-element->bytes", 
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("path-element->string", 
			     scheme_make_immed_prim(path_element_to_string, 
                                                    "path-element->string", 
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("string->path", 
			     scheme_make_immed_prim(string_to_path, 
                                                    "string->path", 
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("bytes->path", 
			     scheme_make_immed_prim(bytes_to_path, 
                                                    "bytes->path", 
                                                    1, 2), 
			     env);
  scheme_addto_prim_instance("bytes->path-element", 
			     scheme_make_immed_prim(bytes_to_path_element, 
                                                    "bytes->path-element", 
                                                    1, 2), 
			     env);
  scheme_addto_prim_instance("string->path-element", 
			     scheme_make_immed_prim(string_to_path_element, 
                                                    "string->path-element", 
                                                    1, 1), 
			     env);

  scheme_addto_prim_instance("file-exists?", 
			     scheme_make_prim_w_arity(file_exists, 
						      "file-exists?", 
						      1, 1), 
			     env);
  scheme_addto_prim_instance("directory-exists?", 
			     scheme_make_prim_w_arity(directory_exists, 
						      "directory-exists?", 
						      1, 1), 
			     env);
  scheme_addto_prim_instance("link-exists?", 
			     scheme_make_prim_w_arity(link_exists, 
						      "link-exists?", 
						      1, 1), 
			     env);
  scheme_addto_prim_instance("delete-file", 
			     scheme_make_prim_w_arity(delete_file, 
						      "delete-file", 
						      1, 1), 
			     env);
  scheme_addto_prim_instance("rename-file-or-directory", 
			     scheme_make_prim_w_arity(rename_file, 
						      "rename-file-or-directory", 
						      2, 3), 
			     env);
  scheme_addto_prim_instance("copy-file", 
			     scheme_make_prim_w_arity(copy_file, 
						      "copy-file", 
						      2, 3), 
			     env);
  scheme_addto_prim_instance("build-path", 
			     scheme_make_immed_prim(scheme_build_path,
                                                    "build-path", 
                                                    1, -1), 
			     env);
  scheme_addto_prim_instance("build-path/convention-type", 
			     scheme_make_immed_prim(build_path_kind,
                                                    "build-path/convention-type", 
                                                    2, -1), 
			     env);
  scheme_addto_prim_instance("path->directory-path",
			     scheme_make_immed_prim(path_to_directory_path,
                                                    "path->directory-path",
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("split-path", 
			     scheme_make_prim_w_arity2(split_path,
						       "split-path",
						       1, 1,
						       3, 3), 
			     env);
  scheme_addto_prim_instance("explode-path", 
			     scheme_make_immed_prim(explode_path,
                                                    "explode-path",
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("relative-path?", 
			     scheme_make_immed_prim(relative_path_p,
                                                    "relative-path?",
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("absolute-path?", 
			     scheme_make_immed_prim(absolute_path_p,
                                                    "absolute-path?",
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("complete-path?", 
			     scheme_make_immed_prim(complete_path_p,
                                                    "complete-path?",
                                                    1, 1), 
			     env);
  scheme_addto_prim_instance("path->complete-path",
			     scheme_make_immed_prim(path_to_complete_path,
                                                    "path->complete-path",
                                                    1, 2), 
			     env);
  scheme_addto_prim_instance("resolve-path",
			     scheme_make_prim_w_arity(resolve_path,
						      "resolve-path",
						      1, 1), 
			     env);
  scheme_addto_prim_instance("simplify-path",
			     scheme_make_prim_w_arity(scheme_simplify_path,
						      "simplify-path",
						      1, 2), 
			     env);
  scheme_addto_prim_instance("cleanse-path",
			     scheme_make_prim_w_arity(cleanse_path,
						      "cleanse-path",
						      1, 1), 
			     env);
  scheme_addto_prim_instance("expand-user-path",
			     scheme_make_prim_w_arity(expand_user_path,
						      "expand-user-path",
						      1, 1), 
			     env);
  scheme_addto_prim_instance("directory-list",
			     scheme_make_prim_w_arity(directory_list,
						      "directory-list",
						      0, 1), 
			     env);
  scheme_addto_prim_instance("filesystem-root-list",
			     scheme_make_prim_w_arity(filesystem_root_list,
						      "filesystem-root-list",
						      0, 0), 
			     env);
  scheme_addto_prim_instance("make-directory",
			     scheme_make_prim_w_arity(make_directory,
						      "make-directory",
						      1, 1), 
			     env);
  scheme_addto_prim_instance("delete-directory",
			     scheme_make_prim_w_arity(delete_directory,
						      "delete-directory",
						      1, 1), 
			     env);
  scheme_addto_prim_instance("make-file-or-directory-link",
			     scheme_make_prim_w_arity(make_link,
						      "make-file-or-directory-link",
						      2, 2), 
			     env);
  scheme_addto_prim_instance("file-or-directory-modify-seconds",
			     scheme_make_prim_w_arity(file_modify_seconds,
						      "file-or-directory-modify-seconds",
						      1, 3), 
			     env);
  scheme_addto_prim_instance("file-or-directory-permissions",
			     scheme_make_prim_w_arity(file_or_dir_permissions,
						      "file-or-directory-permissions",
						      1, 2), 
			     env);
  scheme_addto_prim_instance("file-or-directory-identity",
			     scheme_make_prim_w_arity(file_identity,
						      "file-or-directory-identity",
						      1, 2), 
			     env);
  scheme_addto_prim_instance("file-size",
			     scheme_make_prim_w_arity(file_size,
						      "file-size",
						      1, 1), 
			     env);

  scheme_addto_prim_instance("current-drive", 
			     scheme_make_prim_w_arity(current_drive, 
						      "current-drive", 
						      0, 0), 
			     env);

  scheme_addto_prim_instance("find-system-path", 
			     scheme_make_prim_w_arity(find_system_path, 
						      "find-system-path", 
						      1, 1), 
			     env);

  scheme_addto_prim_instance("current-directory",
			     scheme_register_parameter(current_directory,
						       "current-directory", 
						       MZCONFIG_CURRENT_DIRECTORY),
			     env);
  scheme_addto_prim_instance("current-directory-for-user",
			     scheme_register_parameter(current_user_directory,
						       "current-directory-for-user", 
						       MZCONFIG_CURRENT_USER_DIRECTORY),
			     env);
  scheme_addto_prim_instance("current-force-delete-permissions",
			     scheme_register_parameter(current_force_delete_perms,
						       "current-force-delete-permissions",
						       MZCONFIG_FORCE_DELETE_PERMS),
			     env);
}

void scheme_init_file_places()
{
  REGISTER_SO(original_pwd);
}

/**********************************************************************/
/*                             paths                                  */
/**********************************************************************/

Scheme_Object *scheme_make_sized_offset_kind_path(char *chars, intptr_t d, intptr_t len, int copy, int kind)
{
  Scheme_Object *s;
  s = scheme_make_sized_offset_byte_string(chars, d, len, copy);
  s->type = kind;
  return s;
}

Scheme_Object *scheme_make_sized_offset_path(char *chars, intptr_t d, intptr_t len, int copy)
{
  return scheme_make_sized_offset_kind_path(chars, d, len, copy, SCHEME_PLATFORM_PATH_KIND);
}

# define IS_SPEC_CHAR(x) (IS_A_DOS_SEP(x) || ((x) == '"') || ((x) == '|') || ((x) == ':') || ((x) == '<') || ((x) == '>'))
static int is_special_filename(const char *_f, int offset, int len, int not_nul, int immediate);

static Scheme_Object *make_protected_sized_offset_path(int protect, char *chars, 
						       intptr_t d, intptr_t len, int copy,
						       int just_check, int kind)
     /* just_check == 2 => just check, and only for the case
	that it's the last element of a path */
{
  if (kind == SCHEME_WINDOWS_PATH_KIND) {
    if (protect) {
      int i;

      protect = 0;

      if (!protect) {
        int at_end = 1;
        for (i = len; i--; ) {
          if ((just_check != 2)
              && ((chars[i + d] == '.')
                  || (chars[i + d] == ' '))) {
            if (at_end) {
              protect = 1;
              break;
            }
          } else {
            at_end = 0;
            if ((chars[i + d] == '/')
                || (IS_SPEC_CHAR(chars[i + d]))) {
              protect = 1;
              break;
            }
          }
        }
      }

      if (!protect && (len == 1) && (chars[d] == '.'))
        protect = 1;

      if (!protect && (len == 2) && (chars[d] == '.') && (chars[d+1] == '.'))
        protect = 1;

      if (!protect) 
        protect = is_special_filename(chars, d, len, 0, 1);

      if (protect) {
        char *s2;
        if (just_check)
          return scheme_true;
        s2 = (char *)scheme_malloc_atomic(len + 9 + 1);
        memcpy(s2, "\\\\?\\REL\\\\", 9);
        memcpy(s2 + 9, chars + d, len);
        s2[9 + len] = 0;
        return scheme_make_sized_offset_kind_path(s2, 0, len + 9, 0, SCHEME_WINDOWS_PATH_KIND);
      }
    }
  } else {
#ifdef TILDE_IS_ABSOLUTE
    if (protect) {
      if (chars[d] == '~') {
        char *nm;
        if (just_check)
          return scheme_true;
        nm = (char *)scheme_malloc_atomic(len + 3);
        memcpy(nm XFORM_OK_PLUS 2, chars XFORM_OK_PLUS d, len);
        nm[0] = '.';
        nm[1] = '/';
        nm[len + 2] = 0;
        return scheme_make_sized_offset_kind_path(nm, 0, len + 2, 0, kind);
      }
    }
#endif
  }

  if (just_check)
    return scheme_false;

  return scheme_make_sized_offset_kind_path(chars, d, len, copy, kind);
}

#ifdef DOS_FILE_SYSTEM
static Scheme_Object *make_protected_path(char *chars)
{
  return make_protected_sized_offset_path(1, chars, 0, strlen(chars), 1, 0, SCHEME_WINDOWS_PATH_KIND);
}
#endif

Scheme_Object *make_exposed_sized_offset_path(int *optional, int already_protected, 
					      char *chars, intptr_t d, intptr_t len, int copy,
                                              int kind)
  /* Called to make a directory path where the end has been removed.
     We may need to remove a redundant separator.
     Under Windows, if the resulting last element has spaces or is a 
     special file, then we need to protect it with "\\?\". */
{
  if (kind == SCHEME_WINDOWS_PATH_KIND) {
    if (!already_protected) {
      int i, name_end;
      int non_dot = 0, trailing_dots = 0, protect = 0;
      /* Skip trailing seps: */
      for (i = d + len - 1; (i > d) && IS_A_DOS_SEP(chars[i]); --i) {
      }
      name_end = i+1;
      for (; (i > d) && !IS_A_DOS_SEP(chars[i]); --i) {
        if ((chars[i] != ' ') && (chars[i] != '.'))
          non_dot = 1;
        else if (!non_dot)
          trailing_dots = 1;
      }
      if (non_dot && trailing_dots)
        protect = 1;
      else if (name_end == (d + len))
        protect = is_special_filename(chars, i+1, name_end, 0, 1);

      if (protect) {
        Scheme_Object *first, *last, *a[2];
        char *s2;
        int l;
        l = name_end - (i+1);
        s2 = (char *)scheme_malloc_atomic(l + 9 + 1);
        memcpy(s2, "\\\\?\\REL\\\\", 9);
        memcpy(s2+9, chars + i + 1, l);
        s2[l + 9] = 0;
        last = scheme_make_sized_offset_kind_path(s2, 0, l+9, 0, SCHEME_WINDOWS_PATH_KIND);
        first = make_exposed_sized_offset_path(NULL, 0, chars, d, i-d+1, 1, SCHEME_WINDOWS_PATH_KIND);
        a[0] = first;
        a[1] = last;
        return scheme_build_path(2, a);
      }
    }
  }

  /* We may need to remove a redundant separator from the directory
     path. Try removing it, and see if anyone would care: */
  if (do_path_to_directory_path(chars, d, len - 1, scheme_true, 1, kind)) {
    /* Actually, don't remove a separator after a drive, although it's
       technically redundant. */
    if ((kind != SCHEME_WINDOWS_PATH_KIND)
        || !((len == 3) && is_drive_letter(chars[d]) && (chars[d+1] == ':'))) {
      len--;
      copy = 1;
    }
  }

  if (optional) {
    *optional = len;
    return NULL;
  }

  return scheme_make_sized_offset_kind_path(chars, d, len, copy, kind);
}

Scheme_Object *scheme_make_path(const char *chars)
{
  return scheme_make_sized_offset_path((char *)chars, 0, -1, 1);
}

Scheme_Object *scheme_make_sized_path(char *chars, intptr_t len, int copy)
{
  return scheme_make_sized_offset_path(chars, 0, len, copy);
}

Scheme_Object *scheme_make_path_without_copying(char *chars)
{
  return scheme_make_sized_offset_path(chars, 0, -1, 0);
}

Scheme_Object *scheme_char_string_to_path(Scheme_Object *p)
{
#ifdef DOS_FILE_SYSTEM
  p = scheme_char_string_to_byte_string(p);
#else
  p = scheme_char_string_to_byte_string_locale(p);
#endif
  p->type = SCHEME_PLATFORM_PATH_KIND;
  return p;
}


static Scheme_Object *path_p(int argc, Scheme_Object **argv)
{
  return (SCHEME_PATHP(argv[0]) ? scheme_true : scheme_false);
}

static Scheme_Object *general_path_p(int argc, Scheme_Object **argv)
{
  return (SCHEME_GENERAL_PATHP(argv[0]) ? scheme_true : scheme_false);
}

static Scheme_Object *path_kind(int argc, Scheme_Object **argv)
{
  if (SCHEME_GENERAL_PATHP(argv[0])) {
    switch (SCHEME_PATH_KIND(argv[0])) {
    case SCHEME_WINDOWS_PATH_KIND:
      return windows_symbol;
      break;
    default:
    case SCHEME_UNIX_PATH_KIND:
      return unix_symbol;
      break;
    }
  } else {
    scheme_wrong_contract("path-system-type", "path-for-some-system?", 0, argc, argv);
    return NULL;
  }
}

static Scheme_Object *platform_path_kind(int argc, Scheme_Object **argv)
{
  switch (SCHEME_PLATFORM_PATH_KIND) {
  case SCHEME_WINDOWS_PATH_KIND:
    return windows_symbol;
    break;
  default:
  case SCHEME_UNIX_PATH_KIND:
    return unix_symbol;
    break;
  }
}

static Scheme_Object *drop_rel_prefix(Scheme_Object *p)
/* Drop \\?\REL\ prefix */
{
  int drive_end;
  if (check_dos_slashslash_qm(SCHEME_PATH_VAL(p),
                              SCHEME_PATH_LEN(p),
                              &drive_end, NULL, NULL)) {
    if (drive_end < 0) {
      /* \\?\REL\ */
      int delta;
      if (SCHEME_PATH_VAL(p)[8] == '\\')
        delta = 9;
      else
        delta = 8;
      p = scheme_make_sized_offset_kind_path(SCHEME_BYTE_STR_VAL(p),
                                             delta,
                                             SCHEME_BYTE_STRLEN_VAL(p) - delta,
                                             1,
                                             SCHEME_WINDOWS_PATH_KIND);
    }
  }

  return p;
}

Scheme_Object *scheme_path_to_char_string(Scheme_Object *p)
{
  Scheme_Object *s;

#ifdef DOS_FILE_SYSTEM
  s = scheme_byte_string_to_char_string(p);
#else
  s = scheme_byte_string_to_char_string_locale(p);
#endif

  if (!SCHEME_CHAR_STRLEN_VAL(s))
    return scheme_make_utf8_string("?");
  else
    return s;
}

static Scheme_Object *path_to_string(int argc, Scheme_Object **argv)
{
  if (!SCHEME_PATHP(argv[0]))
    scheme_wrong_contract("path->string", "path?", 0, argc, argv);

  return scheme_path_to_char_string(argv[0]);
}

static Scheme_Object *path_to_bytes(int argc, Scheme_Object **argv)
{
  if (!SCHEME_GENERAL_PATHP(argv[0]))
    scheme_wrong_contract("path->bytes", "path?", 0, argc, argv);

  return scheme_make_sized_byte_string(SCHEME_PATH_VAL(argv[0]),
				       SCHEME_PATH_LEN(argv[0]),
				       1);
}

static Scheme_Object *is_path_element(Scheme_Object *p)
{
  Scheme_Object *base, *fn;
  int isdir;

  fn = scheme_split_path(SCHEME_PATH_VAL(p), 
                         SCHEME_PATH_LEN(p), 
                         &base, 
                         &isdir,
                         SCHEME_PATH_KIND(p));

  if (SCHEME_SYMBOLP(base)
      && SCHEME_GENERAL_PATHP(fn))
    return fn;
  return NULL;
}

static Scheme_Object *do_path_element_to_bytes(const char *name, int argc, Scheme_Object **argv)
{
  Scheme_Object *p = argv[0], *pe;
  int kind;

  if (!SCHEME_GENERAL_PATHP(p))
    scheme_wrong_contract(name, "path?", 0, argc, argv);
  
  pe = is_path_element(p);

  if (!pe)
    scheme_contract_error(name,
                          "path can be split or is not relative",
                          "path", 1, p,
                          NULL);

  if (SCHEME_SYMBOLP(pe)) {
    scheme_contract_error(name,
                          (SAME_OBJ(pe, up_symbol)
                           ? "path is an up-directory indicator"
                           : "path is a same-directory indicator"),
                          "path", 1, p,
                          NULL);
  }

  p = pe;

  kind = SCHEME_PATH_KIND(p);

  if (kind == SCHEME_UNIX_PATH_KIND) {
#ifdef TILDE_IS_ABSOLUTE
    /* Drop ./ of ./~ prefix */
    if ((SCHEME_PATH_VAL(p)[0] == '.')
        && (SCHEME_PATH_VAL(p)[1] == '/')
        && (SCHEME_PATH_VAL(p)[2] == '~')) {
      p = scheme_make_sized_offset_byte_string(SCHEME_PATH_VAL(p), 
                                               2, 
                                               SCHEME_PATH_LEN(p) - 2, 
                                               1);
    }
#endif
  }
  if (kind == SCHEME_WINDOWS_PATH_KIND) {
    p = drop_rel_prefix(p);
  }

  return scheme_make_sized_byte_string(SCHEME_PATH_VAL(p),
				       SCHEME_PATH_LEN(p),
				       1);
}

static Scheme_Object *path_element_to_bytes(int argc, Scheme_Object **argv)
{
  return do_path_element_to_bytes("path-element->bytes", argc, argv);
}

static Scheme_Object *path_element_to_string(int argc, Scheme_Object **argv)
{
  Scheme_Object *b;
  b = do_path_element_to_bytes("path-element->string", argc, argv);
  return scheme_byte_string_to_char_string_locale(b);
}

static void check_path_ok(const char *who, Scheme_Object *p, Scheme_Object *o)
{
  if (has_null(SCHEME_PATH_VAL(p), SCHEME_PATH_LEN(p))) {
    raise_null_error(who, o, "");
  }
}

static Scheme_Object *string_to_path(int argc, Scheme_Object **argv)
{
  Scheme_Object *p;

  if (!SCHEME_CHAR_STRINGP(argv[0]))
    scheme_wrong_contract("string->path", "string?", 0, argc, argv);

  p = scheme_char_string_to_path(argv[0]);
  
  check_path_ok("string->path", p, argv[0]);

  return p;
}

static int extract_path_kind(const char *who, int which, int argc, Scheme_Object **argv)
{
  if (which >= argc)
    return SCHEME_PLATFORM_PATH_KIND;
  
  if (SAME_OBJ(argv[which], windows_symbol))
    return SCHEME_WINDOWS_PATH_KIND;
  if (SAME_OBJ(argv[which], unix_symbol))
    return SCHEME_UNIX_PATH_KIND;

  scheme_wrong_contract(who, "(or/c 'unix 'windows)", which, argc, argv);
  return 0;
}

static Scheme_Object *bytes_to_path(int argc, Scheme_Object **argv)
{
  Scheme_Object *s;
  int kind;

  if (!SCHEME_BYTE_STRINGP(argv[0]))
    scheme_wrong_contract("bytes->path", "bytes?", 0, argc, argv);
  kind = extract_path_kind("bytes->path", 1, argc, argv);

  s = scheme_make_sized_byte_string(SCHEME_BYTE_STR_VAL(argv[0]),
				    SCHEME_BYTE_STRLEN_VAL(argv[0]),
				    SCHEME_MUTABLEP(argv[0]));
  s->type = kind;

  check_path_ok("bytes->path", s, argv[0]);

  return s;
}

static Scheme_Object *do_bytes_to_path_element(const char *name, Scheme_Object *s, int argc, Scheme_Object **argv)
{
  Scheme_Object *p;
  intptr_t i, len;
  int kind;

  if (!SCHEME_BYTE_STRINGP(s))
    scheme_wrong_contract(name, "bytes?", 0, argc, argv);
  kind = extract_path_kind(name, 1, argc, argv);

  len = SCHEME_BYTE_STRLEN_VAL(s);
  for (i = 0; i < len; i++) {
    if (IS_A_PRIM_SEP(kind, SCHEME_BYTE_STR_VAL(s)[i])) {
      break;
    }
  }

  if (i >= len) {
    if (len == 0)
      p = NULL;
    else
      p = make_protected_sized_offset_path(1, SCHEME_BYTE_STR_VAL(s),
                                           0, len,
                                           SCHEME_MUTABLEP(s), 0,
                                           kind);
  } else
    p = NULL;
  
  if (!p || !is_path_element(p))
    scheme_contract_error(name,
                          "cannot be converted to a path element",
                          "path", 1, argv[0],
                          "explanation", 0, (len 
                                             ? "path can be split, is not relative, or names a special element"
                                             : "path element cannot be empty"),
                          NULL);

  return p;
}

static Scheme_Object *bytes_to_path_element(int argc, Scheme_Object **argv)
{
  return do_bytes_to_path_element("bytes->path-element", argv[0], argc, argv);
}

static Scheme_Object *string_to_path_element(int argc, Scheme_Object **argv)
{
  Scheme_Object *b;

  if (!SCHEME_CHAR_STRINGP(argv[0]))
    scheme_wrong_contract("string->path-element", "string?", 0, argc, argv);

  b = scheme_char_string_to_byte_string_locale(argv[0]);
  
  return do_bytes_to_path_element("string->path-element", b, argc, argv);
}

/**********************************************************************/
/*                                                                    */
/**********************************************************************/

char *scheme_os_getcwd(char *buf, int buflen, int *actlen, int noexn)
{
  char *s;
  int slen;

  s = rktio_get_current_directory(scheme_rktio);
  if (!s) {
    if (noexn) {
      /* We need to invent some complete path. */
#ifdef DOS_FILE_SYSTEM
      s = MSC_IZE(strdup)("C:\\");
#else
      s = strdup("/");
#endif
    } else {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                       "current-directory: unknown failure\n"
                       "  system error: %R");
      return NULL;
    }
  }

  slen = strlen(s);

  if (actlen)
    *actlen = slen+1;

  if (buflen < slen) {
    return scheme_strdup_and_free(s);
  } else {
    memcpy(buf, s, slen+1);
    free(s);
    return buf;
  }
}

int scheme_os_setcwd(char *expanded, int noexn)
{
  if (!rktio_set_current_directory(scheme_rktio, expanded)) {
    if (!noexn)
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
		       "current-directory: unable to switch to directory\n"
                       "  path: %q\n"
                       "  system error: %R",
		       expanded);
    return 0;
  }

  return 1;
}

#ifdef DOS_FILE_SYSTEM

static intptr_t wc_strlen(const wchar_t *ws)
{
  intptr_t l;
  for (l =0; ws[l]; l++) { }
  return l;
}

wchar_t *scheme_path_to_wide_path(const char *who, const char *p)
{
  wchar_t *wp, *gc_wp;
  intptr_t len;
  
  wp = rktio_path_to_wide_path(scheme_rktio, p);
  if (wp) {
    len = wc_strlen(wp);
    gc_wp = scheme_malloc_atomic((len + 1) * sizeof(wchar_t));
    memcpy(gc_wp, wp, (len + 1) * sizeof(wchar_t));
    free(wp);
    return gc_wp;
  }
  if (who)
    scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                     "%s: could not read file\n"
                     "  path: %q\n"
                     "  system error: %R",
                     p);

  return NULL;
}
#endif

Scheme_Object *scheme_get_file_directory(const char *filename)
{
  int isdir;
  Scheme_Object *base;
  
  scheme_split_path(filename, strlen(filename), &base, &isdir, SCHEME_PLATFORM_PATH_KIND);
  
  return base;
}

Scheme_Object *scheme_remove_current_directory_prefix(Scheme_Object *fn)
{
  Scheme_Object *cwd;
  intptr_t len;

  cwd = scheme_get_param(scheme_current_config(), MZCONFIG_CURRENT_USER_DIRECTORY);

  fn = TO_PATH(fn);

  len = SCHEME_PATH_LEN(cwd);
  if ((len < SCHEME_PATH_LEN(fn))
      && !scheme_strncmp(SCHEME_PATH_VAL(cwd), SCHEME_PATH_VAL(fn), len)) {
    /* Skip over path separators: */
    while (IS_A_SEP(SCHEME_PLATFORM_PATH_KIND, SCHEME_PATH_VAL(fn)[len])) {
      len++;
    }

    return scheme_make_sized_offset_path(SCHEME_PATH_VAL(fn), len, SCHEME_PATH_LEN(fn) - len, 1);
  }

  return fn;
}

static int has_null(const char *s, intptr_t l)
{
  if (!l)
    return 1;

  while (l--) {
    if (!s[l])
      return 1;
  }

  return 0;
}

static void raise_null_error(const char *name, Scheme_Object *path, const char *mod)
{
  if (!(SCHEME_CHAR_STRINGP(path) ? SCHEME_CHAR_STRTAG_VAL(path) : SCHEME_PATH_LEN(path)))
    scheme_raise_exn(MZEXN_FAIL_CONTRACT,
		     "%s: path string%s is empty", 
		     name, mod);
  else
    scheme_raise_exn(MZEXN_FAIL_CONTRACT,
		     "%s: path string%s contains a null character\n"
                     "  path string: %Q", 
		     name, mod, 
		     path);
}

static int check_dos_slashslash_qm(const char *next, int len, 
				   int *drive_end, int *clean_start, int *add_sep)
/* Check starting with exactly \\?\, which prefixes an absolute path
   to be passed on to the filesystem without changes.

   If it's a \\?\ path, then drive_end is set to the first character
   after the root specification. For example, if the drive is
   terminated by \\\ (a weird "root"), then drive_end is set to after
   the third \.  If the drive is \\?\C:\, then drive_end is after the
   last slash, unless thre's one extra slash, in which case drive_end
   is after that slash, too. In the case of \\?\UNC\..., drive_end
   is after the UNC part as in check_dos_slashslash_drive(). If
   it's a \\?\REL\ or \\?\RED\ path, then drive_end is set to -1(!)
   or -2(!)!; use get_slashslash_qm_dot_ups_end() to get more information.

   clean_start is the position where it's ok to start removing
   extra slahes. It's usually set to the same thing as drive_end. In the
   case of a \\?\UNC\ path, clean_start is set to 7 (i.e., just after
   that prefix). In the case of a \\?\REL\ or \\?\RED\ path, clean_start
   is the end of the string.

   If add_sep is set, it points to a place where an extra separator
   might need to be inserted.
*/
{
  if ((len >= 4)
      && (next[0] == '\\')
      && (next[1] == '\\')
      && (next[2] == '?')
      && (next[3] == '\\')) {
    int base;
    if (!drive_end && !clean_start && !add_sep)
      return 1;
    if (next[4] == '\\')
      base = 5;
    else
      base = 4;
    /* If there's two backslashes in a row at the end, count everything
       as the drive. There are two exceptions: two backslashes are ok
       at the end in the form \\?\C:\\, and \\?\\\ is \\?\ */
    if ((len > 5)
	&& (next[len - 1] == '\\')
	&& (next[len - 2] == '\\')) {
      if (len == 6) {
	/* \\?\ is the root */
      } else if ((len != 8)
	  || !is_drive_letter(next[base])
	  || (next[base+1] != ':')) {
	if (drive_end)
	  *drive_end = len;
	if (clean_start)
	  *clean_start = len;
	if (add_sep)
	  *add_sep = len;
	return 1;
      }
    }
    /* If there's three backslashes in a row, count everything
       up to the slashes as the drive. */
    if (len > 6) {
      int i;
      for (i = len; --i > 5; ) {
	if ((next[i] == '\\')
	    && (next[i-1] == '\\')
	    && (next[i-2] == '\\')) {
	  if (drive_end)
	    *drive_end = i+1;
	  if (clean_start)
	    *clean_start = i+1;
	  return 1;
	}
      }
    }

    if ((len > 6)
	&& is_drive_letter(next[base])
	&& next[base+1] == ':'
	&& next[base+2] == '\\') {
      if (clean_start)
	*clean_start = base+2;
      if (drive_end) {
	if ((len > base+3) && next[base+3] == '\\')
	  *drive_end = base+4;
	else
	  *drive_end = base+3;
      }
    } else if ((len > base+3)
	       && ((next[base] == 'U') || (next[base] == 'u'))
	       && ((next[base+1] == 'N') || (next[base+1] == 'n'))
	       && ((next[base+2] == 'C') || (next[base+2] == 'c'))
	       && (next[base+3] == '\\')
	       && check_dos_slashslash_drive(next, 
					     (((len > (base+4)) && (next[base+4] == '\\'))
					      ? base+5
					      : base+4),
					     len, drive_end, 0, 1)) {
      /* drive_end set by check_dos_slashslash_drive */
      if (clean_start)
	*clean_start = base+3;
    } else if ((base == 4) 
	       && (len > 8)
	       && (next[4] == 'R')
	       && (next[5] == 'E')
	       && ((next[6] == 'L') || (next[6] == 'D'))
	       && (next[7] == '\\')
	       && ((next[8] != '\\')
		   || (len > 9))) { 
      if (drive_end)
	*drive_end = ((next[6] == 'L') ? -1 : -2);
      if (clean_start)
	*clean_start = len; /* caller will have to use get_slashslash_qm_dot_ups_end */
    } else {
      if (drive_end)
	*drive_end = 4;
      if (clean_start) {
	if (((len == 5) && (next[4] == '\\'))
	    || ((len == 6) && (next[4] == '\\') && (next[5] == '\\')))
	  *clean_start = 3;
	else
	  *clean_start = 4;
      }
      if (add_sep)
	*add_sep = 4;
    }
    return 1;
  }
  return 0;
}

static int check_dos_slashslash_drive(const char *next, int delta, int len, 
				      int *drive_end, int exact, int no_fw)
/* Returns 1 if this path is a UNC path, 0 otherwise.
   (It starts by checking for \\?\ paths, so they won't be
   treated as UNC. Unless delta is non-0, in which case the
   check isn't necessary, presumably because the original
   `next' already started with \\?\UNC\.)
   For a 1 result, drive_end (if not NULL) is set to point to the
   byte after the \\server\vol; so, drive_end points to either
   a separator or NUL char.
   If exact is 1, then a 1 is returned only if `next' is just the
   drive; that is, only if 1 would be returned and only slashes are
   in `next' starting with `*drive_end'.
   If `no_fw' is set, then only backslashes are recognized.
*/
{
  int j;
  int is_drive = 0;

  if (drive_end)
    *drive_end = len;

  if (!delta && check_dos_slashslash_qm(next, len, NULL, NULL, NULL))
    return 0;

#define IS_X_SEP(c) (no_fw ? (c == '\\') : IS_A_DOS_SEP(c))

  if (delta || (IS_A_DOS_SEP(next[0]) && IS_A_DOS_SEP(next[1]))) {
    /* Found two separators... */
    /* Check for a drive form: //x/y */
    j = delta ? delta : 2;
    if (!IS_X_SEP(next[j])) {
      /* Found non-sep; skip over more */
      for (; j < len; j++) {
	if (IS_X_SEP(next[j])) {
	  /* Found sep again, so we have //x/: */
	  j++;
	  if (no_fw && (j < len) && IS_X_SEP(next[j]))
	    j++; /* two backslashes ok in \\?\UNC mode */
	  if ((j == (delta ? (delta + 2) : 4))
	      && (next[j - 2] == '?')) {
	    /* We have //?/, with up to 2 backslashes.
	       This doesn't count as UNC, to avoid confusion with \\?\. */
	  } else if ((j < len) && !IS_X_SEP(next[j])) {
	    /* Found non-sep again; this is UNC */
	    for (; j < len; j++) {
	      if (IS_X_SEP(next[j])) {
		/* Found sep again. */
		if (drive_end)
		  *drive_end = j;
		if (exact) {
		  for (; j < len; j++) {
		    if (!IS_X_SEP(next[j])) {
		      /* Found non-sep again 
			 - not a drive (it's absolute path) */
		      break;
		    }
		  }
		} else
		  is_drive = 1;
		break;
	      }
	    }
	    if (j >= len)
	      is_drive = 1;
	    break;
	  }
	  break;
	} else if (IS_A_DOS_SEP(next[j])) {
	  /* Found / when only \ is allowed as separator */
	  break;
	}
      }
    }
  }

  return is_drive;
}

static int get_slashslash_qm_dot_ups_end(const char *s, int len, int *_lit_start)
  /* If str is of the form \\?\REL\..\..\.., returns the index just
     past the last "\..". This might be the first "\" of a "\\"
     separator, the "\" before a non-".." element, or the end of the
     string. For a \\?\RED\ path, it's as if there are no ".."s
     (because ".." is not special in "RED" paths).  The _lit_start
     value is filled with the starting index of the literal part of
     the path (i.e., after one or two slashes). */
{
  int pos = -1, j = 7; /* \\?\REL\ or \\?\RED\ */

  if (s[6] == 'L') {
    while (1) {
      if (j + 3 > len) {
        break;
      } else if ((s[j] == '\\') && (s[j+1] == '.') && (s[j+2] == '.')
                 && ((j + 3 == len) || (s[j+3] == '\\'))) {
        pos = j + 3;
        j += 3;
      } else {
        break;
      }
    }
  }

  if (pos > 0) {
    if (pos == len) 
      *_lit_start = len;
    else if ((pos + 2 < len)
	     && s[pos+1] == '\\') {
      *_lit_start = pos + 2;
    } else {
      *_lit_start = pos + 1;
    }
  } else if (len > 8) {
    if (s[8] == '\\')
      *_lit_start = 9;
    else
      *_lit_start = 8;
  } else
    *_lit_start = len;

  return pos;
}

static char *convert_to_backslashbackslash_qm(char *cleaned, int *_clen, char *str, int *_alloc, int len)
     /* cleaned (bad name) is input; str must be NULL or at least
	*_clen + 10; alloc is size of str; result maybe goes into str,
	but new srt may be returned, and result length is in
	*_clen. len is amount extract expected to be useful in str. */
{
  int clen = *_clen, pos;
  int alloc = *_alloc;

  if (!str) {
    alloc = clen + 10;
    str = scheme_malloc_atomic(alloc);
  }

  {
    int cde = 0;
    if (!check_dos_slashslash_drive(cleaned, 0, clen, &cde, 0, 0))
      cde = 0;
    cleaned = remove_redundant_slashes(cleaned, &clen, cde, NULL, SCHEME_WINDOWS_PATH_KIND);
  }
  cleaned = do_normal_path_seps(cleaned, &clen, 0, 1, SCHEME_WINDOWS_PATH_KIND, NULL);
  if (scheme_is_relative_path(cleaned, clen, SCHEME_WINDOWS_PATH_KIND)) {
    memcpy(str, "\\\\?\\REL\\", 8);
    memcpy(str + 8, cleaned, clen);
    pos = clen + 8;
  } else {
    int plen, xdel = 0;
    if (cleaned[0] == '\\') {
      if (cleaned[1] == '\\') {
        /* UNC */
        xdel = 1;
        plen = 7;
        pos = 0; /* reset below */
      } else {
        /* Drive-relative absolute. */
        memcpy(str, "\\\\?\\RED\\", 8);
        memcpy(str + 8, cleaned, clen);
        pos = clen + 8;
        plen = 0;
      }
    } else {
      plen = 4;
      pos = 0; /* reset below */
    }
    if (plen) {
      memcpy(str, "\\\\?\\UNC", plen);
      memcpy(str + plen, cleaned + xdel, clen - xdel);
      pos = clen + plen - xdel;
    }
  }

  *_alloc = alloc;
  *_clen = pos;
  return str;
}

static char *get_drive_part(const char *wds, int wdlen)
{
  int dend, dstart = 0;
  char *naya;

  if (check_dos_slashslash_qm(wds, wdlen, &dend, NULL, NULL)) {
    /* dend can't be < 0, because that's a relative path */
  } else if (!check_dos_slashslash_drive(wds, 0, wdlen, &dend, 0, 0))
    dend = 3;

  naya = scheme_malloc_atomic(dend + 1);
  memcpy(naya + dstart, wds, dend);
  naya[dend] = 0;

  return naya;
}

char *scheme_getdrive()
{
  scheme_security_check_file("current-drive", NULL, SCHEME_GUARD_FILE_EXISTS);
#ifdef DOS_FILE_SYSTEM
  {
    Scheme_Object *wd;
    wd = CURRENT_WD();
    return get_drive_part(SCHEME_PATH_VAL(wd), SCHEME_PATH_LEN(wd));
  }
#else
  return "";
#endif
}

char *strip_trailing_spaces(const char *s, int *_len, int delta, int in_place)
  /* Strips trailing dots, too */
{
  int len, skip_end = 0;

  if (_len)
    len = *_len;
  else
    len = strlen(s);

  /* Keep separators that are at the very end: */
  if ((len - skip_end > delta) && IS_A_DOS_SEP(s[len - 1 - skip_end])) {
    skip_end++;
  }

  if ((len - skip_end > delta) 
      && ((s[len - 1 - skip_end] == ' ') || (s[len - 1 - skip_end] == '.'))) {
    char *t;
    int orig_len = len;

    while ((len - skip_end > delta) 
	   && ((s[len - 1 - skip_end] == ' ') || (s[len - 1 - skip_end] == '.'))) {
      len--;
    }

    /* If the path element doesn't contain any non-space non-. chars, don't
       strip them after all. */
    if ((len - skip_end > delta) && !IS_A_DOS_SEP(s[len - 1 - skip_end])) {
      if (in_place)
	t = (char *)s;
      else {
	t = (char *)scheme_malloc_atomic(len + 1);
	memcpy(t, s, len - skip_end);
      }
      memcpy(t + len - skip_end, t + orig_len - skip_end, skip_end);
      t[len] = 0;
      
      if (_len)
	*_len = len;
      
      return t;
    }
  }

  return (char *)s;
}

/* Watch out for special device names. Could we do better than hardwiring this list? */
READ_ONLY static const char *special_filenames[] = { "NUL", "CON", "PRN", "AUX", /* NT only: "CLOCK$", */
                                     "COM1", "COM2", "COM3", "COM4", "COM5", 
                                     "COM6", "COM7", "COM8", "COM9",
                                     "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", 
                                     "LPT6", "LPT7", "LPT8", "LPT9", NULL };

static int is_special_filename(const char *f, int offset, int len, int not_nul, int immediate)
{
  int i, j, delta;

  /* Skip over path: */
  if (!len)
    return 0;
  if (!immediate) {
    delta = len;
    if (check_dos_slashslash_qm(f, delta, NULL, NULL, NULL))
      return 0;
    delta -= 1;
    while (delta && !IS_A_DOS_SEP(f[delta])) {
      --delta;
    }
    if (!delta && is_drive_letter(f[0]) && f[1] == ':') {
      delta = 2;
    } else if (IS_A_DOS_SEP(f[delta]))
      delta++;
  } else
    delta = offset;

  for (i = not_nul; special_filenames[i]; i++) {
    const char *sf = special_filenames[i];
    for (j = 0; sf[j] && f[delta + j]; j++) {
      if (scheme_toupper((mzchar)(unsigned char)f[delta + j]) != sf[j])
	break;
    }
    if (j && !sf[j]) {
      j += delta;
      if ((j >= (len + offset))
	  || (f[j] == '.')
	  || (f[j] == ':'))
	return i + 1;
      while ((j < (len + offset))
	     && ((f[j] == ' ')
		 || (f[j] == '.'))) {
	j++;
      }
      if (j >= (len + offset))
	return i + 1;

      return 0;
    }
  }

  return 0;
}

#ifdef DOS_FILE_SYSTEM
int scheme_is_special_filename(const char *f, int not_nul)
{
  return is_special_filename(f, 0, strlen(f), not_nul, 0);
}
#else
int scheme_is_special_filename(const char *f, int not_nul)
{
  return 0;
}
#endif

static char *remove_redundant_slashes(char *filename, int *l, int delta, int *expanded, int kind)
{
  int extra = 0, i, ilen = *l;
  
  for (i = ilen; --i > delta; ) {
    if (IS_A_SEP(kind, filename[i])) {
      if (IS_A_SEP(kind, filename[i - 1])) {
        extra++;
      }
    }
  }

  if (extra) {
    char *naya;
    naya = (char *)scheme_malloc_atomic(ilen + 1 - extra);
    extra = 0;
    for (i = delta; i < ilen; i++) {
      if (IS_A_SEP(kind, filename[i])
          && IS_A_SEP(kind, filename[i + 1])) {
        /* Skip */
        extra++;
      } else {
        naya[i - extra] = filename[i];
      }
    }
    memcpy(naya, filename, delta);
    ilen -= extra;
    naya[ilen] = 0;
    filename = naya;
    if (expanded)
      *expanded = 1;
  }
  
  *l = ilen;
  return filename;
}

static char *do_expand_filename(Scheme_Object *o, char* filename, int ilen, const char *errorin, 
				int *expanded,
				int report_bad_user, int fullpath,
				int guards, int kind, int expand_user)
{
  if (expanded)
    *expanded = 0;

  if (o) {
    o = TO_PATH(o);
    filename = SCHEME_PATH_VAL(o);
    ilen = SCHEME_PATH_LEN(o);
  }

  if (guards)
    scheme_security_check_file(errorin, filename, guards);

  if (ilen < 0)
    ilen = strlen(filename);
  else  {
    if (has_null(filename, ilen)) {
      if (errorin)
	raise_null_error(errorin, scheme_make_sized_path(filename, ilen, 1), "");
      else 
	return NULL;
    }
  }

  if (kind == SCHEME_UNIX_PATH_KIND) {
    /* User home lookup strategy taken from wxWindows: */

#ifdef UNIX_FILE_SYSTEM
    if (expand_user && (filename[0] == '~')) {
      char *new_filename;
      new_filename = rktio_expand_user_tilde(scheme_rktio, filename);
      if (!new_filename) {
        scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                         "%s: bad username in path\n"
                         "  path: %q\n"
                         "  system error: %R", 
                         errorin, filename);
      }

      filename = scheme_strdup_and_free(new_filename);
      ilen = strlen(filename);
      if (expanded)
        *expanded = 1;
    }
#endif

    /* Remove redundant slashes */
    {
      int l = ilen;
      filename = remove_redundant_slashes(filename, &l, 0, expanded, SCHEME_PLATFORM_PATH_KIND);
      ilen = l;
    }
  } else {
    /* SCHEME_WINDOWS_PATH_KIND */
    int drive_end, clean_start;
    int fixit = 0, i, insert_initial_sep = 0;

    if (!check_dos_slashslash_qm(filename, ilen, &drive_end, &clean_start, NULL))
      drive_end = 0;
    else if (drive_end < 0) {
      /* For \\?\REL\, only remove extra backslashes after 
	 unprotected ..s, so count the start of that area
	 as the drive end. */
      get_slashslash_qm_dot_ups_end(filename, ilen, &drive_end);
      /* Make sure that backslashes are doubled after dots. */
      if ((drive_end != ilen) && (filename[drive_end-2] != '\\')) {
	insert_initial_sep = 1;
	fixit = 1;
      }
    } else if (drive_end == 8) {
      /* For \\?\c:\\ path, start clean up after colon. */
      if (is_drive_letter(filename[4])
	  && (filename[5] == ':'))
	drive_end = 6;
    } else if (drive_end == 9) {
      /* For \\?\\c:\\ path, start clean up after colon. */
      if ((filename[4] == '\\')
	  && is_drive_letter(filename[5])
	  && (filename[6] == ':'))
	drive_end = 7;
    } else {
      drive_end = clean_start;
    }

    /* Check whether to clean up the name, removing mulitple // and
       adding "/" after "c:" if necessary */
    if (!drive_end 
	&& is_drive_letter(filename[0])
	&& (filename[1] == ':') 
	&& !IS_A_DOS_SEP(filename[2])) {
      drive_end = 2;
      insert_initial_sep = 1;
      fixit = 1;
    } else {
      int found_slash = 0, prim_only = drive_end;
      
      for (i = ilen; i-- > drive_end; ) {
	if (IS_A_DOS_X_SEP(prim_only, filename[i])) {
	  if (IS_A_DOS_X_SEP(prim_only, filename[i - 1])) {
	    if ((i > 1) || !found_slash)
	      fixit = 1;
	    break;
	  }
	  found_slash = 1;
	}
      }
    }

    if (fixit) {
      int pos, prim_only = drive_end;
      char *naya;
      
      if (expanded)
	*expanded = 1;
      
      if (!drive_end) {
	/* Allow // at start? */
	if (check_dos_slashslash_drive(filename, 0, ilen, NULL, 0, 0))
	  drive_end = 2;
      }

      naya = (char *)scheme_malloc_atomic(ilen + 2);

      memcpy(naya, filename, drive_end);
      pos = i = drive_end;
      if (insert_initial_sep) {
	naya[pos++] = '\\';
      }
      
      while (i < ilen) {
	if (IS_A_DOS_X_SEP(prim_only, filename[i])
            && ((i + 1) < ilen)
	    && IS_A_DOS_X_SEP(prim_only, filename[i + 1])) {
	  i++;
	} else
	  naya[pos++] = filename[i++];
      }
      
      naya[pos] = 0;
      filename = naya;
      ilen = pos;

      if (drive_end == 4) {
	/* If the root was \\?\, there's a chance that we removed a
	   backslash and changed the root. In that case, add two \\s after \\?\: */
	check_dos_slashslash_qm(filename, ilen, &drive_end, NULL, NULL);
	if (drive_end != 4) {
	  /* There's room to expand, because insert_initial_sep couldn't be -1. */
	  if (filename[4] == '\\') {
	    /* Need one more */
	    memmove(filename + 5, filename + 4, ilen - 3);
	    filename[4] = '\\'; /* Actually, this is redundant. */
	    ilen += 1;
	  } else {
	    /* Need two more */
	    memmove(filename + 6, filename + 4, ilen - 3);
	    filename[4] = '\\'; /* Actually, this is redundant. */
	    filename[5] = '\\';
	    ilen += 2;
	  }
	}
      }
    }
  }

  if (fullpath) {
    if (!scheme_is_complete_path(filename, ilen, kind)) {
      if (expanded)
	*expanded = 1;
      filename = do_path_to_complete_path(filename, ilen, NULL, 0, kind);
      ilen = strlen(filename);
    }
    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      if (ilen > ((fullpath > 1) ? fullpath : 259)) {
        if (!check_dos_slashslash_qm(filename, ilen, NULL, NULL, NULL)) {
          /* Convert to \\?\ to avoid length limit. */
          int l = ilen, a = ilen + 1;
          Scheme_Object *p;

          p = scheme_make_sized_path(filename, ilen, 0);
          p = do_simplify_path(p, scheme_null, 0, 0, 0, SCHEME_WINDOWS_PATH_KIND, 0);
          filename = SCHEME_PATH_VAL(p);
          ilen = SCHEME_PATH_LEN(p);

          filename = convert_to_backslashbackslash_qm(filename, &l, filename, &a, 0);
          filename[l] = 0;
        }
      }
    }
  }

  return filename;
}

char *scheme_expand_filename(char* filename, int ilen, const char *errorin, int *expanded, int guards)
{
  return do_expand_filename(NULL, filename, ilen, errorin, expanded, 1, 1, guards, SCHEME_PLATFORM_PATH_KIND, 0);
}

char *scheme_expand_user_filename(char* filename, int ilen, const char *errorin, int *expanded, int guards)
{
  return do_expand_filename(NULL, filename, ilen, errorin, expanded, 1, 1, guards, SCHEME_PLATFORM_PATH_KIND, 1);
}

char *scheme_expand_string_filename(Scheme_Object *o, const char *errorin, int *expanded, int guards)
{
  return do_expand_filename(o, NULL, 0, errorin, expanded, 1, 1, guards, SCHEME_PLATFORM_PATH_KIND, 0);
}

#define MZ_UNC_READ RKTIO_PERMISSION_READ
#define MZ_UNC_WRITE RKTIO_PERMISSION_WRITE
#define MZ_UNC_EXEC RKTIO_PERMISSION_EXEC

int scheme_file_exists(char *filename)
{
  if (scheme_is_special_filename(filename, 0))
    return 1;
  return rktio_file_exists(scheme_rktio, filename);
}

int scheme_directory_exists(char *dirname)
{
  return rktio_directory_exists(scheme_rktio, dirname);
}

int scheme_is_regular_file(char *filename)
{
  return rktio_is_regular_file(scheme_rktio, filename);
}

static Scheme_Object *file_exists(int argc, Scheme_Object **argv)
{
  char *f;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("file-exists?", "path-string?", 0, argc, argv);

  f = do_expand_filename(argv[0],
			 NULL,
			 0,
			 "file-exists?",
			 NULL,
			 0, 1,
			 SCHEME_GUARD_FILE_EXISTS,
                         SCHEME_PLATFORM_PATH_KIND,
                         0);

  return (f && scheme_file_exists(f)) ? scheme_true : scheme_false;
}

static Scheme_Object *directory_exists(int argc, Scheme_Object **argv)
{
  char *f;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("directory-exists?", "path-string?", 0, argc, argv);

  f = do_expand_filename(argv[0],
			 NULL,
			 0,
			 "directory-exists?",
			 NULL,
			 0, 1,
			 SCHEME_GUARD_FILE_EXISTS,
                         SCHEME_PLATFORM_PATH_KIND,
                         0);

  return (f && scheme_directory_exists(f)) ? scheme_true : scheme_false;
}

static Scheme_Object *link_exists(int argc, Scheme_Object **argv)
{
  char *filename;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("link-exists?", "path-string?", 0, argc, argv);

  filename = do_expand_filename(argv[0],
				NULL,
				0,
				"link-exists?",
				NULL,
				0, 1,
				SCHEME_GUARD_FILE_EXISTS,
				SCHEME_PLATFORM_PATH_KIND,
				0);

  if (rktio_link_exists(scheme_rktio, filename))
      return scheme_true;
    else
      return scheme_false;
}

Scheme_Object *scheme_get_fd_identity(Scheme_Object *port, intptr_t fd, char *path, int noerr)
/* If path is supplied, then fd is 0 for stat, 1 for lstat */
{
  rktio_identity_t *ident;
  Scheme_Object *a, *b, *c, *args[2];

  if (path)
    ident = rktio_path_identity(scheme_rktio, path, fd == 0);
  else {
    rktio_fd_t *rfd;
    rfd = rktio_system_fd(scheme_rktio, fd, RKTIO_OPEN_NOT_REGFILE);
    ident = rktio_fd_identity(scheme_rktio, rfd);
    rktio_forget(scheme_rktio, rfd);
  }

  if (!ident) {
    if (!path) {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                       "port-file-identity: error obtaining identity\n"
                       "  system error: %R");
    } else {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                       "file-or-directory-identity: error obtaining identity for path\n"
                       "  path: %q\n"
                       "  system error: %R",
                       path);
    }
  }

  a = scheme_make_integer_value_from_unsigned(ident->a);
  b = scheme_make_integer_value_from_unsigned(ident->b);
  c = scheme_make_integer_value_from_unsigned(ident->c);

  args[0] = b;
  args[1] = scheme_make_integer(ident->c_bits);
  b = scheme_bitwise_shift(2, args);

  args[0] = a;
  args[1] = scheme_make_integer(ident->c_bits + ident->b_bits);
  a = scheme_bitwise_shift(2, args);

  free(ident);

  return scheme_bin_plus(scheme_bin_plus(a, b), c);
}

static int path_is_simple_dir_without_sep(Scheme_Object *path)
{
  int len;

  len = SCHEME_PATH_LEN(path);
  if (IS_A_SEP(SCHEME_PATH_VAL(path)[len - 1], SCHEME_PATH_KIND(path)))
    return 0;

  /* The simple thing to do here is to use split_path, but that's
     a lot of extra computation. */

  if (SCHEME_PATH_VAL(path)[len - 1] == '.') {
    if (len == 1)
      return 1;
    if (IS_A_SEP(SCHEME_PATH_VAL(path)[len - 2], SCHEME_PATH_KIND(path)))
      return 1;
    if (SCHEME_PATH_VAL(path)[len - 2] == '.') {
      if (len == 2)
        return 1;
      if (IS_A_SEP(SCHEME_PATH_VAL(path)[len - 3], SCHEME_PATH_KIND(path)))
        return 1;
    }
  }

#ifdef TILDE_IS_ABSOLUTE
  if (SCHEME_PATH_KIND(path) == SCHEME_UNIX_PATH_KIND) {
    if (SCHEME_PATH_VAL(path)[0] == '~') {
      int i;
      for (i = 1; i < len; i++) {
        if (IS_A_UNIX_SEP(SCHEME_PATH_VAL(path)[i]))
          break;
      }
      if (i == len)
        return 1;
    }
  }
#endif

  if (SCHEME_PATH_KIND(path) == SCHEME_WINDOWS_PATH_KIND) {
    int drive_end;
    if (check_dos_slashslash_drive(SCHEME_PATH_VAL(path), 0, len, &drive_end, 1, 0))
      return 1; /* exactly a UNC drive */
    if (len == 2
        && (is_drive_letter(SCHEME_PATH_VAL(path)[0]))
        && (SCHEME_PATH_VAL(path)[1] == ':'))
      return 1; /* a c: path */
  }

  return 0;
}

static Scheme_Object *do_path_to_directory_path(char *s, intptr_t offset, intptr_t len, Scheme_Object *p, int just_check,
                                                int kind)
/* Although this function accepts an offset, the Windows part assumes that
   `offset' is always 0. */
{
  char *s2;
#if DROP_REDUNDANT_SLASHES
  int not_a_sep = 0;
#endif

  if (kind == SCHEME_WINDOWS_PATH_KIND) {
    int slash_dir_sep = 1;

    {
      int drive_end;

      if (offset) {
        scheme_signal_error("path->directory-path currently assumes a 0 offset");
      }

      if (check_dos_slashslash_qm(s, len, &drive_end, NULL, NULL)) {
#if DROP_REDUNDANT_SLASHES
        if (drive_end < 0) {
          /* It's a \\?\REL\ or \\?\RED\ path. */
          int litpos;
          drive_end = get_slashslash_qm_dot_ups_end(s, len, &litpos);
          /* If there's no path after the ..s, then nothing more is needed. */
          if (litpos >= len)
            return p;
        } else {
          /* If s is just a drive, then nothing more is needed. */
          if (drive_end == len)
            return p;
        }
#endif

        /* In \\?\, / can be part of a name, and it is never a separator. */
        slash_dir_sep = 0;
        /* Any "." or ".." at the end is a literal path element,
           not an up- or same-directory indicator: */
#if DROP_REDUNDANT_SLASHES
        not_a_sep = 1;
#endif
      } else {
#if DROP_REDUNDANT_SLASHES
        /* A slash after C: is not strictly necessary: */
        if ((len == 2)
            && is_drive_letter(s[offset])
            && (s[offset+1] == ':'))
          return p;
#endif
      }
    }
    {
      int cs = s[offset + len - 1];
      if (slash_dir_sep ? IS_A_DOS_SEP(cs) : (cs == '\\'))
        return p;
    }
  } else {
    if (IS_A_UNIX_SEP(s[offset + len - 1]))
      return p;
  }

#if DROP_REDUNDANT_SLASHES
  if (!not_a_sep
      && (((len > 1) && (s[offset + len - 1] == '.') && IS_A_SEP(kind, s[offset + len - 2]))
          || ((len == 1) && (s[offset] == '.'))))
    return p;
  if (!not_a_sep
      && (((len > 2) 
           && (s[offset + len - 1] == '.') 
           && (s[offset + len - 2] == '.') 
           && IS_A_SEP(kind, s[offset + len - 3]))
          || ((len == 2) && (s[offset] == '.') && (s[offset + 1] == '.'))))
    return p;
  
# ifdef TILDE_IS_ABSOLUTE
  if (kind == SCHEME_UNIX_PATH_KIND) {
    if (s[offset] == '~') {
      intptr_t i;
      for (i = 1; i < len; i++) {
        if (IS_A_UNIX_SEP(s[offset + i]))
          break;
      }
      if (i >= len)
        return p;
    }
  }
# endif
#endif

  if (just_check)
    return NULL;

  s2 = (char *)scheme_malloc_atomic(len + 2);
  memcpy(s2, s XFORM_OK_PLUS offset, len);
  s2[len] = FN_SEP(kind);
  s2[len+1] = 0;

  return scheme_make_sized_offset_kind_path(s2, 0, len + 1, 0, kind);
}

Scheme_Object *scheme_path_to_directory_path(Scheme_Object *p)
{
  return do_path_to_directory_path(SCHEME_PATH_VAL(p), 0, SCHEME_PATH_LEN(p), p, 0, 
                                   SCHEME_PATH_KIND(p));
}

static char *do_normal_path_seps(char *si, int *_len, int delta, int strip_trail, int kind, int *_did)
{
  if (kind == SCHEME_UNIX_PATH_KIND) {
    return si;
  } else {
    int i;
    unsigned char *s;
    int len = *_len;
    
    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      if (!delta && check_dos_slashslash_qm(si, len, NULL, NULL, NULL))
        return si;
    }
    
    s = (unsigned char *)MALLOC_N_ATOMIC(char, len + 1);
    memcpy(s, si, len + 1);
    
    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      for (i = delta; i < len; i++) {
        if (s[i] == '/') {
          if (_did)
            *_did = 1;
          s[i] = '\\';
        }
      }
      if (strip_trail)
        s = (unsigned char *)strip_trailing_spaces((char *)s, _len, delta, 1);
    }
    
    return (char *)s;
  }
}

char *scheme_normal_path_seps(char *si, int *_len, int delta)
{
  return do_normal_path_seps(si, _len, delta, 1, SCHEME_PLATFORM_PATH_KIND, NULL);
}

#define PATH_EXTRA_SPACE 4

static Scheme_Object *do_build_path(int argc, Scheme_Object **argv, int idelta, int no_final_simplify, int kind)
/* Originally, it made sense to just perform build operations
   directly on string representations, because it was simple enough.
   Over the years, though, as we refined the path syntax for Windows
   to deal with all of its idiosyncrasies, this has gotten completely 
   out of hand. */
{
#define PN_BUF_LEN 256
  int pos, i, len, no_sep;
  int alloc = PN_BUF_LEN;
  char buffer[PN_BUF_LEN], *str, *next;
  int rel, next_off;
  int first_was_drive = 0;
  int first_len = 0;
  int needs_extra_slash = 0;
  int pre_unc = 0;
  int pre_qm = 0;
  const char *who = (idelta ? "build-path/convention-type" : "build-path");

  str = buffer;
  pos = 0;

  no_sep = 0; /* This is actually initialized after we know whether
		 it's relative or not. */

  for (i = 0 ; i < argc; i++) {
    if (SCHEME_GENERAL_PATH_STRINGP(argv[i+idelta])
	|| (SCHEME_SYMBOLP(argv[i+idelta]) 
	    && (SAME_OBJ(argv[i+idelta], up_symbol)
		|| SAME_OBJ(argv[i+idelta], same_symbol)))) {
      next_off = 0;
      if (SAME_OBJ(argv[i+idelta], up_symbol)) {
        next = "..";
        len = 2;
      } else if (SAME_OBJ(argv[i+idelta], same_symbol)) {
	next = ".";
	len = 1;
      } else {
	Scheme_Object *bs;

        if (SCHEME_CHAR_STRINGP(argv[i+idelta])) {
          if (kind != SCHEME_PLATFORM_PATH_KIND) {
            scheme_contract_error(who,
                                  (idelta
                                   ? "specified convention incompatible with string path element"
                                   : "preceding path's convention incompatible with string path element"),
                                  "path element", 1, argv[i+idelta],
                                  (idelta ? "convention" : "preceding path's convention"),
                                  0,
                                  (kind == scheme_unix_path_type) ? "'unix" : "'windows",
                                  NULL); 
          }
        }

	bs = TO_PATH(argv[i+idelta]);

        if (kind != SCHEME_PATH_KIND(bs)) {
          scheme_contract_error(who,
                                (idelta
                                 ? "specified convention incompatible with given path element"
                                 : "preceding path's convention incompatible with given path element"),
                                "path element", 1, argv[i+idelta],
                                (idelta ? "convention" : "preceding path's convention"),
                                0,
                                (kind == scheme_unix_path_type) ? "'unix" : "'windows",
                                NULL); 
        }

	next = SCHEME_PATH_VAL(bs);
	len = SCHEME_PATH_LEN(bs);
	if (!len) {
	  char *astr;
	  intptr_t alen;

	  astr = scheme_make_arg_lines_string("   ", i+idelta, argc, argv, &alen);
	  scheme_raise_exn(MZEXN_FAIL_CONTRACT,
			   "%s: path element is an empty string\n"
                           "  argument position: %d%s\n"
                           "  other arguments...:%t", 
                           who,
			   i + 1,
			   scheme_number_suffix(i + 1),
			   astr, alen);
	  return scheme_false;
	}

	if (has_null(next, len)) {
	  raise_null_error(who, argv[i+idelta], " element");
	  return NULL;
	}
      }

      if (kind == SCHEME_WINDOWS_PATH_KIND) {
	/* Strip trailing spaces before we add more path parts,
	   because trailing spaces originally don't count for the base
	   path, and they'll start counting if we add more without
	   removing the spaces first. first_len points after anything
	   that should be saved due to a \\?\ prefix. */
	int p = pos;
	strip_trailing_spaces(str, &p, first_len, 1);
	pos = p;
      }

      /* +3: null term, leading sep, and trailing sep (if up & Mac) */
      if (pos + len + PATH_EXTRA_SPACE >= alloc) {
	char *naya;
	int newalloc;

	newalloc = 2 * alloc + len + 1;
	naya = (char *)scheme_malloc_atomic(newalloc);
	memcpy(naya, str, pos);
	alloc = newalloc;
	
	str = naya;
      }

      if (kind == SCHEME_UNIX_PATH_KIND) {
        if (next[0] == '/') {
          rel = 0;
          if (i) {
            scheme_raise_exn(MZEXN_FAIL_CONTRACT,
                             "%s: absolute path cannot be added to a path\n"
                             "  absolute path: %q",
                             who,
                             next);
            return scheme_false;
          }
        } else {
          rel = 1;
#ifdef TILDE_IS_ABSOLUTE
          if (i && (next[0] == '.') && (next[1] == '/') && (next[2] == '~')) {
            /* Strip the "./" prefix */
            next_off += 2;
            len -= 2;
          }
#endif
        }
      } else {
        /* SCHEME_WINDOWS_PATH_KIND: */
	int is_drive;

	needs_extra_slash = 0;
	
	if (IS_A_DOS_SEP(next[0])) {
	  int drive_end, plus_sep = 0;
	  rel = 0;
	  if (check_dos_slashslash_qm(next, len, &drive_end, NULL, &plus_sep)) {
	    if (drive_end < 0) {
	      /* \\?\REL\ or \\?\RED\ path */
	      rel = 1;
	      is_drive = 0;
	      if (i) {
		int dots_end, lit_start;
		int new_rel_base, need_simplify;
		int base_is_here = 0;

		/* If the current base is not a \\?\ path, turn it into one. */
		if (!check_dos_slashslash_qm(str, pos, &drive_end, NULL, NULL)) {
		  Scheme_Object *simp;

		  str[pos] = 0;
		  simp = do_simplify_path(scheme_make_sized_offset_kind_path(str, 0, pos, 0,
                                                                             SCHEME_WINDOWS_PATH_KIND),
					  scheme_null, first_len, 0, 0,
                                          SCHEME_WINDOWS_PATH_KIND, 0);
		  if (SCHEME_FALSEP(simp)) {
		    /* Base path is just relative "here". We can ignore it. */
		    pos = 0;
		    first_len = len;
		    if (next[len] != '\\')
		      first_len++;
		    no_sep = 1;
		    new_rel_base = 0;
		  } else {
		    char *cleaned;
		    int clen;
		    int al = alloc;

		    clen = SCHEME_PATH_LEN(simp); 
		    cleaned = SCHEME_PATH_VAL(simp);

		    str = convert_to_backslashbackslash_qm(cleaned, &clen, str, &al, 
							   len + PATH_EXTRA_SPACE);

		    pos = clen;
		    alloc = al;
		    
		    if ((pos > 5)
			&& (str[4] == 'R')
			&& (str[5] == 'E'))
		      new_rel_base = 1;
		    else
		      new_rel_base = 0;

		    if (str[pos - 1] != '\\')
		      str[pos++] = '\\';
		    no_sep = 1;
		    first_len = pos;
		  }
		  need_simplify = 0;
		} else {
		  new_rel_base = (drive_end < 0);
		  need_simplify = 1;
		}
		
		if (!pos) {
		  /* Base was relative "here", so we can use next directly */
		} else {
		  dots_end = get_slashslash_qm_dot_ups_end(next, len, &lit_start);
		  
		  if (dots_end > 0) {
		    /* Add dots part of this addition, then simplify again: */
		    if (!no_sep)
		      str[pos++] = '\\';
		    memcpy(str + pos, next + 8, dots_end - 8);
		    pos += dots_end - 8;
		    str[pos] = 0;
		    need_simplify = 1;
		  }

		  if (need_simplify) {
                    /* Simplify the base path to build on: */
		    Scheme_Object *simp;

		    simp = do_simplify_path(scheme_make_sized_offset_kind_path(str, 0, pos, 0,
                                                                               SCHEME_WINDOWS_PATH_KIND),
					    scheme_null, first_len, 0, 1,
                                            SCHEME_WINDOWS_PATH_KIND, 0);
		    if (SCHEME_FALSEP(simp)) {
                      /* Note: if root turns out to be relative, then we couldn't
                         have had a \\?\RED\ path. */
		      memcpy(str, "\\\\?\\REL\\\\", 9);
		      pos = 9;
		      no_sep = 1;
		      base_is_here = 1;
		    } else {
		      pos = SCHEME_PATH_LEN(simp);
		      memcpy(str, SCHEME_PATH_VAL(simp), pos);
		      no_sep = (str[pos - 1] == '\\');
		    }
		  }

		  /* At this point, we may have dots only in a \\?\REL
		     path in str, or we might have something without a 
		     \\ to prevent later .. from being parsed as 'up.
		     So, add a backslash if needed. */
		  if (new_rel_base && (lit_start < len)) {
		    int ls;
		    dots_end = get_slashslash_qm_dot_ups_end(str, pos, &ls);
		    if (dots_end > 0) {
		      if (ls == pos) {
			if (dots_end + 2 > pos) {
			  if (dots_end + 1 > pos)
			    str[pos++] = '\\';
			  str[pos++] = '\\';
			  no_sep = 1;
			}
		      }
		    } else if (ls == 8) {
		      memmove(str + 9, str + 8, pos - 8);
		      str[8] = '\\';
		      pos++;
		      no_sep = 1;
		    } 
		  }

		  /* Set offset into next to get only literal part, and
		     set first_len to indicate that the result will be
		     literal */
		  next_off = lit_start;
		  len -= next_off;
		  if (!len) {
		    if (base_is_here) {
		      /* Special case: base is "here" and path to add is
			 "here". Make sure result is just ".". */
		      pos = 0;
		      no_sep = 1;
		      next = ".";
		      len = 1;
		      next_off = 0;
		    } else
		      no_sep = 1;
		  } else {
		    /* One last possibility: str is \\?\ (which counts as a bizaare
		       root). We need two extra slashes. */
		    if (!new_rel_base && (pos == 4)) {
		      str[pos++] = '\\';
		      str[pos++] = '\\';
		    }
		  }
		  first_len = pos + len;
		  if (next[next_off + len] != '\\')
		    first_len++;
		}
	      } else {
		first_len = len;
	      }
	    } else {
	      /* non-REL/RED \\?\ path */
              is_drive = (drive_end == len);
	      needs_extra_slash = plus_sep;
	      if (!i) {
		first_len = len;
		if (next[first_len - 1] != '\\')
		  first_len++;
	      }
	    }
	  } else
	    is_drive = check_dos_slashslash_drive(next, 0, len, NULL, 1, 0);
	} else if ((len >= 2) 
		   && is_drive_letter(next[0])
		   && (next[1] == ':')) {
	  int j;
	  rel = 0;
	  for (j = 2; j < len; j++) {
	    if (!IS_A_DOS_SEP(next[j]))
	      break;
	  }
	  is_drive = (j >= len);
	} else {
	  rel = 1;
	  is_drive = 0;
	}

	if (!rel) {
	  if (i && (!first_was_drive || (i > 1) || is_drive)) {
	    if (pos > 30) {
	      str[27] = '.';
	      str[28] = '.';
	      str[29] = '.';
	      str[30] = 0;
	    } else
	      str[pos] = 0;
	    scheme_raise_exn(MZEXN_FAIL_CONTRACT,
			     "%s: %s cannot be added to a base path\n"
                             "  %s: %s\n"
                             "  base path: %q",
                             who,
			     is_drive ? "drive" : "absolute path",
			     is_drive ? "drive" : "absolute path",
			     next, str);
	    return scheme_false;
	  }

	  if (i == 1) {
	    /* Absolute path onto a drive: skip separator(s) */
	    while (len && IS_A_DOS_SEP(next[next_off])) {
	      next_off++;
	      len--;
	    }
	  }
	}

	if (!i)
	  first_was_drive = is_drive;
      }

      if (!i) {
	no_sep = 1;
      }
      
      if (kind == SCHEME_WINDOWS_PATH_KIND) {
        if (i) {
          pre_unc = check_dos_slashslash_drive(str, 0, pos, NULL, 0, 0);
	  if (!pre_unc) {
	    int de;
	    if (check_dos_slashslash_qm(str, pos, &de, NULL, NULL)) {
	      if (de == 4) /* \\?\ */
		pre_qm = 1;
	    }
	  } else
	    pre_qm = 0;
        } else {
          pre_unc = 1;
	  pre_qm = 0;
	}

        if (no_final_simplify
            && (len == 2) 
            && (next[next_off] == '.')
            && (next[next_off+1] == '.')
            && (first_len < pos + 2)) {
          /* Adding ".." ... */
          int de;
          if (check_dos_slashslash_qm(str, pos, &de, NULL, NULL)) {
            if (de < 0) {
              /* ... to a \\?\REL\ or \\?\RED\ path. Unless the \\?\REL\ path
                 is only dots, we need to remove a path element
                 here, instead of waiting for simplify, because simplify
                 will just push the job back here. */
              int ls, dots_end;
              dots_end = get_slashslash_qm_dot_ups_end(str, pos, &ls);
              if (ls == pos) {
                /* It's ok to add "..". Make sure we don't
                   append to "..\\" by setting pos to no more
                   than dots_end + 1. */
                if (dots_end < ls)
                  pos = dots_end + 1;
              } else {
                int q;
                for (q = pos; q-- > ls; ) {
                  if (str[q] == '\\') {
                    break;
                  }
                }
                pos = q;
                first_len = pos;
                len = 0;
                while (q && (str[q-1] == '\\')) {
                  q--;
                }
                if (q == 7) {
                  /* All we have left is \\?\REL or \\?\RED (plus a slash or two).
                     We should only get here when called by scheme_simplify. */
                  if (i + 1 == argc) {
                    /* Since we were called by scheme_simplify, use #f to mean
                       the empty path. */
                    return scheme_false;
                  }
                  /* Shouldn't ever get here, but just in case... */
                  str[0] = '.';
                  pos = 1;
                  no_sep = 1;
                  first_len = 0;
                }
              }
            }
          }
        }
      }

      if (!no_sep)
	str[pos++] = FN_SEP(kind);

      memcpy(str + pos, next + next_off, len);
      pos += len;

      if (kind == SCHEME_WINDOWS_PATH_KIND) {
        if (!pre_unc
            && check_dos_slashslash_drive(str, 0, pos, NULL, 0, 0)) {
          /* Added to //x to get something that looks like UNC. Remove the
             first [back]slash. */
          memmove(str, str+1, pos - 1);
          --pos;
        }
	if (pre_qm) {
	  int de;

	  /* Normalize path separators for the addition: */
	  {
	    int i;
	    for (i = first_len; i < pos; i++) {
	      if (str[i] == '/') {
		str[i] = '\\';
	      }
	    }
	  }

	  /* check the \\?\ parsing */
	  check_dos_slashslash_qm(str, pos, &de, NULL, NULL);
	  if (de != 4) {
	    /* Added to \\?\ to get something that now looks like 
	       a \\?\UNC path. Insert a backslash or two. */
	    int amt = ((str[4] == '\\') ? 1 : 2);
	
	    if (pos + amt >= alloc) {
	      char *naya;
	      int newalloc;
	      
	      newalloc = 2 * alloc;
	      naya = (char *)scheme_malloc_atomic(newalloc);
	      memcpy(naya, str, pos);
	      alloc = newalloc;
	      
	      str = naya;
	    }
	    memmove(str + 4 + amt, str + 4, pos - 4);
	    str[4] = '\\';
	    if (amt == 2)
	      str[5] = '\\';
	    pos += amt;
	    first_len += amt;
	  }
	}

        if (needs_extra_slash) {
          if (needs_extra_slash >= pos)
            str[pos++] = '\\';
          else if (str[needs_extra_slash] != '\\') {
            memmove(str + needs_extra_slash + 1, str + needs_extra_slash, pos - needs_extra_slash);
            str[needs_extra_slash] = '\\';
            pos++;
          }
        }
      }

      /* If last path elem ends in a separator, don't add one: */
      if (len) {
	no_sep = IS_A_SEP(kind, next[next_off + len - 1]);
      } else {
	no_sep = 0;
      }
    } else {
      scheme_wrong_contract(who, "(or/c path-for-some-system? path-string? 'up 'same)", i + idelta, argc, argv);
      return scheme_false;
    }
  }

  str[pos] = 0;

  if (kind == SCHEME_WINDOWS_PATH_KIND) {
    if (check_dos_slashslash_qm(str, pos, NULL, NULL, NULL) && !no_final_simplify) {
      /* Clean up additions to \\?\ path */
      int p;
      Scheme_Object *simp;
      p = pos;
      str = do_normal_path_seps(str, &p, first_len, 1, SCHEME_WINDOWS_PATH_KIND, NULL);
      str = remove_redundant_slashes(str, &p, first_len, NULL, SCHEME_WINDOWS_PATH_KIND);
      simp = do_simplify_path(scheme_make_sized_offset_kind_path(str, 0, p, 0, SCHEME_WINDOWS_PATH_KIND),
                              scheme_null, first_len, 0, 1, SCHEME_WINDOWS_PATH_KIND, 0);
      if (SCHEME_FALSEP(simp))
        return scheme_make_sized_offset_kind_path(".\\", 0, 1, 0, SCHEME_WINDOWS_PATH_KIND);
      else
        return simp;
    }
  }

  return scheme_make_sized_offset_kind_path(str, 0, pos, alloc == PN_BUF_LEN, kind);
}

Scheme_Object *scheme_build_path(int argc, Scheme_Object **argv)
{
  int kind = SCHEME_PLATFORM_PATH_KIND, i;

  for (i = 0; i < argc; i++) {
    if (SCHEME_GENERAL_PATHP(argv[i])) {
      kind = SCHEME_PATH_KIND(argv[i]);
      break;
    } else if (SCHEME_CHAR_STRINGP(argv[i])) {
      kind = SCHEME_PLATFORM_PATH_KIND;
      break;
    }
  }
  
  return do_build_path(argc, argv, 0, 0, kind);
}

static Scheme_Object *build_path_kind(int argc, Scheme_Object **argv)
{ 
  int kind;

  kind = extract_path_kind("build-path/convention-type", 0, argc, argv);
  return do_build_path(argc - 1, argv, 1, 0, kind);
}

static Scheme_Object *path_to_directory_path(int argc, Scheme_Object **argv)
{
  Scheme_Object *inpath;

  inpath = argv[0];

  if (!SCHEME_GENERAL_PATH_STRINGP(inpath))
    scheme_wrong_contract("path->directory-path", "(or/c path-for-some-system? path-string?)", 0, argc, argv);

  inpath = TO_PATH(inpath);

  return scheme_path_to_directory_path(inpath);
}

static Scheme_Object *do_split_path(const char *path, int len, 
                                    Scheme_Object **base_out, char **base_str_out, int *base_len_out,
                                    int *id_out,
                                    int *cleaned_slashes, int kind,
                                    int check_repeats)
{
  char *s;
  int p, last_was_sep = 0, is_dir, no_up = 0, not_same;
  Scheme_Object *file;
  int allow_double_before = 0, drive_end, no_slash_sep = 0;

#define MAKE_SPLIT(x, x_str, x_len, y, z) (*base_out = x, *base_str_out = x_str, *base_len_out = x_len, *id_out = z, y)

  s = (char *)path;

  if (kind == SCHEME_WINDOWS_PATH_KIND) {
    if ((len > 2) && IS_A_DOS_SEP(s[0]) && IS_A_DOS_SEP(s[1])) {
      if (check_dos_slashslash_qm(s, len, &drive_end, NULL, NULL)) {
        allow_double_before = drive_end;
        no_slash_sep = 1;
        if (drive_end < 0) {
          /* \\?\REL\ or \\?\RED\ path. Handle it directly as a special case. */
          int p, lit_start, dots_end;
          is_dir = 0;
          if (s[len - 1] == '\\') {
            --len;
            is_dir = 1;
          }
          dots_end = get_slashslash_qm_dot_ups_end(s, len, &lit_start);
          if (lit_start < len) {
            /* There's at least one literal path. */
            for (p = len; --p >= ((dots_end > 0) ? lit_start - 1 : lit_start); ) {
              if (s[p] == '\\') {
                /* Prefix path element with \\?\REL\\: */
                {
                  int len2, nsep;
                  char *s2;
                  len2 = len - p - 1 + 9;
                  s2 = scheme_malloc_atomic(len2 + 1);
                  memcpy(s2, "\\\\?\\REL\\\\", 9);
                  memcpy(s2 + 9, s + p + 1, len - p - 1);
                  s2[len2] = 0;
                  if ((dots_end == p) || (dots_end == p - 1)) {
                    /* stripping the only element: drop reundant separator(s) after .. */
                    nsep = ((dots_end == p) ? 0 : -1);
                  } else {
                    if (s[6] == 'L') {
                      /* preserve separator */
                      nsep = 1;
                    } else {
                      /* preserve one separator, but not two */
                      if (s[p - 1] == '\\')
                        nsep = 0;
                      else
                        nsep = 1;
                    }
                  }
                  file = scheme_make_sized_offset_kind_path(s2, 0, len2, 0, SCHEME_WINDOWS_PATH_KIND);
                  return MAKE_SPLIT(NULL, s, p + nsep, file, is_dir);
                }
              }
            }
          }
          /* Either no literal path elements, or only one element and no dots */
          if (dots_end > 0) {
            /* There are dots (so no literals) */
            if (dots_end - 3 > 8) {
              return MAKE_SPLIT(NULL, s, dots_end - 3, up_symbol, 1);
            } else
              return MAKE_SPLIT(relative_symbol, NULL, 0, up_symbol, 1);
          } else {
            /* No dots, so there must be one element. */
            if (s[6] == 'L') {
              /* keep \\?\REL\ on path, and report 'relative as base */
              return MAKE_SPLIT(relative_symbol, NULL, 0,
                                scheme_make_sized_offset_kind_path(s, 0, len, 1,
                                                                   SCHEME_WINDOWS_PATH_KIND), 
                                is_dir);
            } else {
              /* Switch "D" to "L", and simplify base to just "\\" */
              char *naya;
              Scheme_Object *dir;
              naya = (char *)scheme_malloc_atomic(len + 2);
              memcpy(naya, s, len + 2);
              naya[6] = 'L';
              if (naya[8] != '\\') {
                /* Make sure REL is followed by \\, just in case the element is
                   ".." (i.e., we had \\?\RED\..). */
                memmove(naya + 9, naya + 8, len + 1 - 8);
                naya[8] = '\\';
                len++;
              }
              dir = scheme_make_sized_offset_kind_path("\\", 0, 1, 0,
                                                       SCHEME_WINDOWS_PATH_KIND);
              return MAKE_SPLIT(dir, NULL, 0,
                                scheme_make_sized_offset_kind_path(naya, 0, len, 0,
                                                                   SCHEME_WINDOWS_PATH_KIND), 
                                is_dir);
            }
          }
        } else {
          no_up = 1;
          if ((drive_end < len) && s[drive_end] == '\\') {
            /* Happens with \\?\c:\\, for example. */
            drive_end++;
          }
        }
      } else if (check_dos_slashslash_drive(s, 0, len, &drive_end, 0, 0)) {
        allow_double_before = 1;
        if ((drive_end < len) && IS_A_DOS_SEP(s[drive_end]))
          drive_end++;
      } else
        drive_end = 0;
    } else if ((len > 1) && is_drive_letter(s[0]) && (s[1] == ':')) {
      drive_end = 2;
      if ((drive_end < len) && IS_A_DOS_SEP(s[drive_end]))
        drive_end++;
    } else
      drive_end = 0;
  } else {
    drive_end = 0;
  }

  /* Look for confusing repeated separators (e.g. "x//y") */
  if (check_repeats) {
    for (p = len; p--; ) {
      if (p > allow_double_before) {
        if (IS_A_SEP(kind, s[p]) && IS_A_SEP(kind, s[p - 1])) {
          /* Found it; copy without repeats */
          int q;
          char *old = s;

          if (cleaned_slashes)
            *cleaned_slashes = 1;

          s = (char *)scheme_malloc_atomic(len);
          --len;

          for (p = 0, q = 0; p < allow_double_before; p++) {
            s[q++] = old[p];
          }

          for (; p < len; p++) {
            if (!IS_A_SEP(kind, old[p]) || !IS_A_SEP(kind, old[p + 1]))
              s[q++] = old[p];
          }
          s[q++] = old[len];
          len = q;
          break;
        }
      }
    }
  }

# define IS_A_SPLIT_SEP(x) (((kind == SCHEME_WINDOWS_PATH_KIND) && no_slash_sep) ? (x == '\\') : IS_A_SEP(kind, x))

  if ((kind == SCHEME_WINDOWS_PATH_KIND) && (len <= drive_end))
    p = -1;
  else {
    for (p = len; p--; ) {
      if (IS_A_SPLIT_SEP(s[p])) {
        if (p != len - 1)
          break;
        else
          last_was_sep = 1;
      }
      if (kind == SCHEME_WINDOWS_PATH_KIND) {
	if (p < drive_end)
	  break;
      }
    }
  }
  
  if (kind == SCHEME_UNIX_PATH_KIND) {
#ifdef TILDE_IS_ABSOLUTE
    /* "./~..." can't be split at the beginning. */
    if ((p == 1)
        && s[0] == '.'
        && s[p + 1] == '~') {
      not_same = 1;
      p -= 2;
    } else
#endif
      not_same = 0;
  } else
    not_same = 0;

  if (p < 0) {
    Scheme_Object *dir;

    /* No splitting available. 
       For Unx & DOS, it was relative or exactly root.
       For Mac, it is relative or root with trailing sep. */
    if (kind == SCHEME_UNIX_PATH_KIND) {
      if (s[0] == '/')
        return MAKE_SPLIT(scheme_false, NULL, 0,
                          scheme_make_sized_offset_kind_path(s, 0, len, 1, kind), 1);
#ifdef TILDE_IS_ABSOLUTE
      if (s[0] == '~') {
        /* Strip ending slashes, if any. */
        while (IS_A_UNIX_SEP(s[len - 1])) {
          --len;
        }
        return MAKE_SPLIT(scheme_false, NULL, 0,
                          scheme_make_sized_offset_kind_path(s, 0, len, 1, kind), 1);
      }
#endif
    } else {
      if (IS_A_DOS_SEP(s[0]) || drive_end)
        return MAKE_SPLIT(scheme_false, NULL, 0,
                          scheme_make_sized_offset_kind_path(s, 0, len, 1, kind), 1);
    }

    dir = relative_symbol;

    /* Check for 'up: */
    if (!no_up && (s[0] == '.') && (s[1] == '.')
	&& (2 >= len || IS_A_SEP(kind, s[2]))) {
      file = up_symbol;
      is_dir = 1;
    } else if (!no_up && !not_same && (s[0] == '.') && (1 >= len || IS_A_SEP(kind, s[1]))) {
      file = same_symbol;
      is_dir = 1;
    } else {
      int delta;
      is_dir = last_was_sep;
      delta = 0;
      file = make_protected_sized_offset_path(no_up || is_dir, 
					      s, 0, len - last_was_sep + delta, 1, 0,
                                              kind);
    }
    
    return MAKE_SPLIT(dir, NULL, 0, file, is_dir);
  }
  
  /* Check for 'up and 'same: */
  if (!no_up && (s[p + 1] == '.') && (s[p + 2] == '.')
      && (p + 3 >= len || IS_A_SEP(kind, s[p + 3]))) {
    file = up_symbol;
    is_dir = 1;
  } else if (!no_up && (s[p + 1] == '.') && (p + 2 >= len || IS_A_SEP(kind, s[p + 2]))) {
    file = same_symbol;
    is_dir = 1;
  } else {
    int protected;
    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      protected = no_up || last_was_sep;
    } else  {
      protected = 1;
    }
    file = make_protected_sized_offset_path(protected,
					    s,
					    p + 1, 
					    len - p - last_was_sep - 1, 
					    1, 0, kind);
    is_dir = last_was_sep;
  }
  
  /* Check directory */
  if (p > 0) {
    Scheme_Object *ss;
    int new_len;
    ss = make_exposed_sized_offset_path(&new_len, no_up, s, 0, p + 1, 1, kind);
    if (ss) {
      s = SCHEME_PATH_VAL(ss);
      new_len = SCHEME_PATH_LEN(ss);
    }
    return MAKE_SPLIT(NULL, s, new_len, file, is_dir);
  }
	
  /* p = 0; this means root dir. */
  {
    Scheme_Object *ss;
    if (s[0] == '/')
      ss = scheme_make_sized_offset_kind_path("/", 0, 1, 0, kind);
    else
      ss = scheme_make_sized_offset_kind_path(s, 0, 1, 1, kind);
    return MAKE_SPLIT(ss, NULL, 0, file, is_dir);
  }
}

static Scheme_Object *do_split_path_once(const char *path, int len, 
                                         Scheme_Object **base_out,
                                         int *id_out,
                                         int *cleaned_slashes, int kind)
{
  Scheme_Object *name, *base;
  char *base_str;
  int base_len;

  name = do_split_path(path, len, base_out, &base_str, &base_len, id_out, cleaned_slashes, kind, 1);

  if (!*base_out) {
    base = scheme_make_sized_offset_kind_path(base_str, 0, base_len, 1, kind);
    *base_out = base;
  }

  return name;
}

Scheme_Object *scheme_split_path(const char *path, int len, Scheme_Object **base_out, int *id_out, int kind)
{
  return do_split_path_once(path, len, base_out, id_out, NULL, kind);
}

static Scheme_Object *_split_path(const char *who, int argc, Scheme_Object **argv, int multi)
{
  char *s;
  int is_dir, len;
  Scheme_Object *three[3], *inpath;

  inpath = argv[0];

  if (!SCHEME_GENERAL_PATH_STRINGP(inpath))
    scheme_wrong_contract(who, "(or/c path-for-some-system? path-string?)", 0, argc, argv);

  inpath = TO_PATH(inpath);

  s = SCHEME_PATH_VAL(inpath);
  len = SCHEME_PATH_LEN(inpath);

  if (!len) {
    scheme_contract_error(who,
                          "path is an empty string",
                          NULL);
  }

  if (has_null(s, len))
    raise_null_error(who, inpath, "");

  if (multi) {
    Scheme_Object *l = scheme_null, *name, *base;
    char *next_s;
    int next_len;
    int kind = SCHEME_PATH_KIND(inpath), check = 1;

    while (1) {
      name = do_split_path(s, len, &base, &next_s, &next_len, &is_dir, NULL, kind, check);
      l = scheme_make_pair(name, l);
      if (base) {
        if (SCHEME_FALSEP(base) || SAME_OBJ(base, relative_symbol)) return l;
        return scheme_make_pair(base, l);
      } else {
        s = next_s;
        len = next_len;
      }
      check = 0;
      SCHEME_USE_FUEL(1);
    }
  } else {
    three[1] = scheme_split_path(s, len, &three[0], &is_dir, SCHEME_PATH_KIND(inpath));
    
    three[2] = is_dir ? scheme_true : scheme_false;
    
    return scheme_values(3, three);
  }
}

static Scheme_Object *split_path(int argc, Scheme_Object **argv)
{
  return _split_path("split-path", argc, argv, 0);
}

static Scheme_Object *explode_path(int argc, Scheme_Object **argv)
{
  return _split_path("explode-path", argc, argv, 1);
}

int scheme_is_relative_path(const char *s, intptr_t len, int kind)
{
  if (!len)
    return 0;

  if (kind == SCHEME_UNIX_PATH_KIND) {
    return !((s[0] == '/') || WHEN_TILDE_IS_ABSOLUTE(s[0] == '~'));
  } else {
    int dlen;
    if (check_dos_slashslash_qm(s, len, &dlen, NULL, NULL)
	&& (dlen < 0)) {
      if (dlen == -1)
        return 1; /* It's a \\?\REL\ path */
      else
        return 0; /* It's a \\?\RED\ path */
    }

    if (IS_A_DOS_SEP(s[0])
        || ((len >= 2) 
            && is_drive_letter(s[0])
            && (s[1] == ':')))
      return 0;
    else
      return 1;
  }
}

int scheme_is_complete_path(const char *s, intptr_t len, int kind)
{
  if (!len)
    return 0;

  if (!kind)
    kind = SCHEME_PLATFORM_PATH_KIND;

  if (!scheme_is_relative_path(s, len, kind)) {
    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      if (IS_A_DOS_SEP(s[0]) && IS_A_DOS_SEP(s[1])) {
        int dlen;
        if (check_dos_slashslash_qm(s, len, &dlen, NULL, NULL)) { /* not relative */
          return (dlen >= 0);
        } else if (check_dos_slashslash_drive(s, 0, len, NULL, 0, 0))
          return 1;
        else
          return 0;
      } else if ((len >= 2) 
                 && is_drive_letter(s[0])
                 && (s[1] == ':')) {
        return 1;
      } else
        return 0;
    } else
      return 1;
  } else 
    return 0;
}

static char *do_path_to_complete_path(char *filename, intptr_t ilen, const char *wrt, intptr_t wlen, int kind)
{
  if (!scheme_is_complete_path(filename, ilen, kind)) {
    char *naya;
    int skip_sep = 0;

    if (!wrt) {
      Scheme_Object *wd;
      if (scheme_current_thread) {
        wd = CURRENT_WD();
        wrt = SCHEME_PATH_VAL(wd);
        wlen = SCHEME_PATH_LEN(wd);
        scheme_security_check_file("path->complete-path", NULL, SCHEME_GUARD_FILE_EXISTS);
      } else {
        int actlen;
        wrt = scheme_os_getcwd(NULL, 0, &actlen, 1);
        wlen = actlen - 1;
      }
    }

    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      if (!scheme_is_relative_path(filename, ilen, kind)) {
        /* Absolute, not complete. Fill in the disk */
        wrt = get_drive_part(wrt, wlen);
        wlen = strlen(wrt);
        /* drop trailing separator */
        if (IS_A_DOS_SEP(wrt[wlen - 1]) 
            && !check_dos_slashslash_qm(wrt, wlen, NULL, NULL, NULL)) {
          wlen--;
        }
        skip_sep = 1;
      }

      if (check_dos_slashslash_qm(wrt, wlen, NULL, NULL, NULL) /* wrt is never relative */
          || check_dos_slashslash_qm(filename, ilen, NULL, NULL, NULL)) { /* filename might be \\?\REL\ */
        /* For \\?\, give up on fast path and use build-path */
        Scheme_Object *a[2], *p;
        p = scheme_make_sized_offset_kind_path((char *)wrt, 0, wlen, 1, SCHEME_WINDOWS_PATH_KIND);
        a[0] = p;
        p = scheme_make_sized_offset_kind_path(filename, 0, ilen, 1, SCHEME_WINDOWS_PATH_KIND);
        a[1] = p;
        p = do_build_path(2, a, 0, 0, SCHEME_WINDOWS_PATH_KIND);
        return SCHEME_PATH_VAL(p);
      }
    }

    naya = (char *)scheme_malloc_atomic(ilen + wlen + 2);
    memcpy(naya, wrt, wlen);
    if (!skip_sep)
      if (!IS_A_SEP(kind, naya[wlen - 1]))
	naya[wlen++] = FN_SEP(kind);
    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      int w = wlen;
      strip_trailing_spaces(naya, &w, 0, 1);
      wlen = w;
    }
    memcpy(naya + wlen, filename, ilen);
    naya[wlen + ilen] = 0;

    return naya;
  }

  return filename;
}

static Scheme_Object *path_to_complete_path(int argc, Scheme_Object **argv)
{
  Scheme_Object *p, *wrt;
  char *s;
  int len, kind;

  p = argv[0];
  if (!SCHEME_GENERAL_PATH_STRINGP(p))
    scheme_wrong_contract("path->complete-path", "(or/c path-for-some-system? path-string?)", 0, argc, argv);
  p = TO_PATH(p);
  if (argc > 1) {
    wrt = argv[1];
    if (!SCHEME_GENERAL_PATH_STRINGP(wrt))
      scheme_wrong_contract("path->complete-path", "(or/c path-for-some-system? path-string?)", 1, argc, argv);
    wrt = TO_PATH(wrt);
  } else
    wrt = NULL;

  kind = SCHEME_PATH_KIND(p);
  if (wrt) {
    if (SCHEME_PATH_KIND(wrt) != kind) {
      scheme_contract_error("path->complete-path",
                            "convention of first path incompatible with convention of second path",
                            "first path", 1, argv[0],
                            "second path", 1, argv[1],
                            NULL);
    }
  } else if (kind != SCHEME_PLATFORM_PATH_KIND) {
    scheme_contract_error("path->complete-path",
                          "no second path supplied, and given path is not for the current platform",
                          "given path", 1, argv[0],
                          NULL);
  }

  s = SCHEME_PATH_VAL(p);
  len = SCHEME_PATH_LEN(p);

  if (has_null(s, len))
    raise_null_error("path->complete-path", p, "");

  if (wrt) {
    char *ws;
    int wlen;

    ws = SCHEME_PATH_VAL(wrt);
    wlen = SCHEME_PATH_LEN(wrt);
    
    if (has_null(ws, wlen))
      raise_null_error("path->complete-path", p, "");

    if (!scheme_is_complete_path(ws, wlen, kind))
      scheme_contract_error("path->complete-path", "second argument is not a complete path",
                            "first argument", 1, p,
                            "second argument", 1, wrt,
                            NULL);
    
    if (!scheme_is_complete_path(s, len, kind)) {
      s = do_path_to_complete_path(s, len, ws, wlen, kind);
      return scheme_make_sized_offset_kind_path(s, 0, strlen(s), 0, kind);
    }
  } else if (!scheme_is_complete_path(s, len, kind)) {
    s = do_path_to_complete_path(s, len, NULL, 0, kind);

    return scheme_make_sized_offset_kind_path(s, 0, strlen(s), 0, kind);
  }
   
  return p;
}

Scheme_Object *scheme_path_to_complete_path(Scheme_Object *path, Scheme_Object *relto_path)
{
  Scheme_Object *a[2];
  a[0] = path;
  a[1] = relto_path;
  return path_to_complete_path(relto_path ? 2 : 1, a);
}

static char *filename_for_error(Scheme_Object *p)
{
  return do_expand_filename(p, NULL, 0,
			    NULL,
			    NULL,
			    1, 1,
			    0, SCHEME_PLATFORM_PATH_KIND,
                            0);
}

int scheme_can_enable_write_permission(void)
{
#ifdef DOS_FILE_SYSTEM
  if (SCHEME_TRUEP(scheme_get_param(scheme_current_config(), MZCONFIG_FORCE_DELETE_PERMS)))
    return 1;
#endif
  return 0;
}

static Scheme_Object *delete_file(int argc, Scheme_Object **argv)
{
  char *fn;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("delete-file", "path-string?", 0, argc, argv);

  fn = scheme_expand_string_filename(argv[0],
                                     "delete-file",
                                     NULL,
                                     SCHEME_GUARD_FILE_DELETE);

  if (!rktio_delete_file(scheme_rktio, fn, scheme_can_enable_write_permission())) {
    scheme_raise_exn(MZEXN_FAIL_FILESYSTEM, 
                     "delete-file: cannot delete file\n"
                     "  path: %q\n"
                     "  system error: %R",
                     filename_for_error(argv[0]));
  }

  return scheme_void;
}

static Scheme_Object *rename_file(int argc, Scheme_Object **argv)
{
  int exists_ok = 0;
  char *src, *dest;
  Scheme_Object *bss, *bsd;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("rename-file-or-directory", "path-string?", 0, argc, argv);
  if (!SCHEME_PATH_STRINGP(argv[1]))
    scheme_wrong_contract("rename-file-or-directory", "path-string?", 1, argc, argv);
  if (argc > 2)
    exists_ok = SCHEME_TRUEP(argv[2]);

  bss = argv[0];
  bsd = argv[1];

  src = scheme_expand_string_filename(bss,
				      "rename-file-or-directory",
				      NULL,
				      SCHEME_GUARD_FILE_READ);
  dest = scheme_expand_string_filename(bsd,
				       "rename-file-or-directory",
				       NULL,
				       SCHEME_GUARD_FILE_WRITE);

  if (!rktio_rename_file(scheme_rktio, dest, src, exists_ok)) {
    if (scheme_last_error_is_racket(RKTIO_ERROR_EXISTS)) {
      /* We use a specialized error message here, because it's not
         a system error. */
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM_EXISTS,
                       "rename-file-or-directory: cannot rename file or directory;\n"
                       " the destination path already exists\n"
                       "  source path: %q\n"
                       "  dest path: %q",
                       filename_for_error(argv[0]),
                       filename_for_error(argv[1]));
    } else {
      scheme_raise_exn((exists_ok < 0) ? MZEXN_FAIL_FILESYSTEM_EXISTS : MZEXN_FAIL_FILESYSTEM, 
                       "rename-file-or-directory: cannot rename file or directory\n"
                       "  source path: %q\n"
                       "  dest path: %q\n"
                       "  system error: %R",
                       filename_for_error(argv[0]),
                       filename_for_error(argv[1]));
    }
  }

  return scheme_void;
}

static void escape_during_copy(rktio_file_copy_t *cf)
{
  rktio_copy_file_stop(scheme_rktio, cf);
}
  
static Scheme_Object *copy_file(int argc, Scheme_Object **argv)
{
  char *src, *dest;
  int exists_ok = 0;
  Scheme_Object *bss, *bsd;
  rktio_file_copy_t *cf;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("copy-file", "path-string?", 0, argc, argv);
  if (!SCHEME_PATH_STRINGP(argv[1]))
    scheme_wrong_contract("copy-file", "path-string?", 1, argc, argv);

  bss = argv[0];
  bsd = argv[1];
  exists_ok = ((argc > 2) && SCHEME_TRUEP(argv[2]));

  src = scheme_expand_string_filename(bss,
                                      "copy-file",
                                      NULL,
                                      SCHEME_GUARD_FILE_READ);
  
  dest = scheme_expand_string_filename(bsd,
                                       "copy-file",
                                       NULL, 
                                       SCHEME_GUARD_FILE_WRITE | SCHEME_GUARD_FILE_DELETE);

  cf = rktio_copy_file_start(scheme_rktio, dest, src, exists_ok);
  if (cf) {
    int ok = 1;
    while (!rktio_copy_file_is_done(scheme_rktio, cf)) {
      if (!rktio_copy_file_step(scheme_rktio, cf)) {
        ok = 0;
        break;
      }
      ok++;
      if (ok == 10) {
        BEGIN_ESCAPEABLE(escape_during_copy, cf);
        SCHEME_USE_FUEL(1);
        END_ESCAPEABLE();
        ok = 1;
      }
    }

    if (ok) {
      if (!rktio_copy_file_finish_permissions(scheme_rktio, cf)) {
        rktio_copy_file_stop(scheme_rktio, cf);
        scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                         "copy-file: cannot set destination's permissions\n"
                         "  source path: %q\n"
                         "  destination path: %q",
                         filename_for_error(argv[0]),
                         filename_for_error(argv[1]));
      }
    }
    rktio_copy_file_stop(scheme_rktio, cf);
    if (ok)
      return scheme_void;
  }
  
  if (scheme_last_error_is_racket(RKTIO_ERROR_EXISTS)) {
    /* We use a specialized error message here, because it's not
       a system error. */
    scheme_raise_exn(MZEXN_FAIL_FILESYSTEM_EXISTS,
                     "copy-file: destination exists\n"
                     "  source path: %q\n"
                     "  destination path: %q",
                     filename_for_error(argv[0]),
                     filename_for_error(argv[1]));
  } else {
    const char *how;

    switch (rktio_get_last_error_step(scheme_rktio)) {
    case RKTIO_COPY_STEP_OPEN_SRC:
      how = "cannot open source file";
      break;
    case RKTIO_COPY_STEP_OPEN_DEST:
      how = "cannot open destination file";
      break;
    case RKTIO_COPY_STEP_READ_SRC_DATA:
      how = "error reading source file";
      break;
    case RKTIO_COPY_STEP_WRITE_DEST_DATA:
      how = "error writing destination file";
      break;
    case RKTIO_COPY_STEP_READ_SRC_METADATA:
      how = "error reading source-file metadata";
      break;
    case RKTIO_COPY_STEP_WRITE_DEST_METADATA:
      how = "error writing destination-file metadata";
      break;
    default:
      how = "copy failed";
    }

    scheme_raise_exn(MZEXN_FAIL_FILESYSTEM, 
                     "copy-file: %s\n"
                     "  source path: %q\n"
                     "  destination path: %q\n"
                     "  system error: %R",
                     how,
                     filename_for_error(argv[0]),
                     filename_for_error(argv[1]));
  }

  return NULL;
}

static Scheme_Object *relative_path_p(int argc, Scheme_Object **argv)
{
  char *s;
  int len;
  Scheme_Object *bs;

  if (!SCHEME_GENERAL_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("relative-path?", "(or/c path-for-some-system? path-string?)", 0, argc, argv);

  bs = TO_PATH(argv[0]);

  s = SCHEME_PATH_VAL(bs);
  len = SCHEME_PATH_LEN(bs);

  if (has_null(s, len))
    return scheme_false;

  return (scheme_is_relative_path(s, len, SCHEME_PATH_KIND(bs))
	  ? scheme_true
	  : scheme_false);
}

static Scheme_Object *complete_path_p(int argc, Scheme_Object **argv)
{
  char *s;
  int len;
  Scheme_Object *bs;

  if (!SCHEME_GENERAL_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("complete-path?", "(or/c path-for-some-system? path-string?)", 0, argc, argv);

  bs = TO_PATH(argv[0]);

  s = SCHEME_PATH_VAL(bs);
  len = SCHEME_PATH_LEN(bs);

  if (has_null(s, len))
    return scheme_false;

  return (scheme_is_complete_path(s, len, SCHEME_PATH_KIND(bs))
	  ? scheme_true
	  : scheme_false);
}

static Scheme_Object *absolute_path_p(int argc, Scheme_Object **argv)
{
  char *s;
  int len;
  Scheme_Object *bs;

  if (!SCHEME_GENERAL_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("absolute-path?", "(or/c path-for-some-system? path-string?)", 0, argc, argv);

  bs = TO_PATH(argv[0]);

  s = SCHEME_PATH_VAL(bs);
  len = SCHEME_PATH_LEN(bs);

  if (has_null(s, len))
    return scheme_false;

  return (!scheme_is_relative_path(s, len, SCHEME_PATH_KIND(bs))
	  ? scheme_true
	  : scheme_false);
}

static Scheme_Object *do_resolve_path(int argc, Scheme_Object *argv[], int guards)
{
  char *content, *filename;
  int expanded;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("resolve-path", "path-string?", 0, argc, argv);

  filename = do_expand_filename(argv[0],
				NULL,
				0,
				"resolve-path",
				&expanded,
				1, 0,
				guards ? SCHEME_GUARD_FILE_EXISTS : 0,
                                SCHEME_PLATFORM_PATH_KIND,
                                0);

  {
    char *fullfilename = filename;
    intptr_t len;
    int copied = 0;

    len = strlen(fullfilename);
    if (!scheme_is_complete_path(fullfilename, len, SCHEME_PLATFORM_PATH_KIND)) {
      fullfilename = do_path_to_complete_path(fullfilename, len, NULL, 0, SCHEME_PLATFORM_PATH_KIND);
      copied = 1;
    }

    /* Make sure path doesn't have trailing separator: */
    len = strlen(fullfilename);
    while (len && IS_A_SEP(SCHEME_PLATFORM_PATH_KIND, fullfilename[len - 1])) {
      if (!expanded && !copied) {
	fullfilename = scheme_strdup(fullfilename);
	copied = 1;
      }
      fullfilename[--len] = 0;
    }

    content = rktio_readlink(scheme_rktio, fullfilename);

    /* Treating all errors (such as link cycles) as `RKTIO_ERROR_NOT_A_LINK` */

    if (content) {
      Scheme_Object *r;
      r = scheme_make_sized_path(content, -1, 1);
      free(content);
      return r;
    }
  }

  if (!expanded && SCHEME_PATHP(argv[0]))
    return argv[0];
  else
    return scheme_make_sized_path(filename, strlen(filename), 1);
}

static Scheme_Object *resolve_path(int argc, Scheme_Object *argv[])
{
  return do_resolve_path(argc, argv, 1);
}

static Scheme_Object *convert_literal_relative(Scheme_Object *file)
{
  int ln;
  char *f;
  f = SCHEME_PATH_VAL(file);
  ln = SCHEME_PATH_LEN(file);
  if ((ln == 11) && !strcmp(f, "\\\\?\\REL\\\\.."))
    return up_symbol;
  else if ((ln == 10) && !strcmp(f, "\\\\?\\REL\\\\."))
    return same_symbol;
  return file;
}

static Scheme_Object *simplify_qm_path(Scheme_Object *path)
{
  /* path is already expanded, so the only remaining
     clean-ups are dropping a trailing separator,
     and getting rid of \\?\ if it's not actually needed. */
  char *s = SCHEME_PATH_VAL(path);
  int drive_end, clean_start, len = SCHEME_PATH_LEN(path), fixed = 0, i;
  int drop_extra_slash = -1, set_slash = -1, element_start;
  int found_bad = 0, start_special_check = 0, is_dir = 0, norm_unc = 0, drop_ss_slash = 0;

  if ((s[len - 1] == '\\')
      && (s[len - 2] != '\\')
      && do_path_to_directory_path(s, 0, len - 1, scheme_true, 1, SCHEME_WINDOWS_PATH_KIND)) {
    --len;
    fixed = 1;
  }

  check_dos_slashslash_qm(s, len, &drive_end, &clean_start, NULL);
  if ((drive_end == 7)
      && is_drive_letter(s[4])
      && (s[5] == ':')) {
    /* Maybe don't need \\?\ for \\?\C:\... */
    start_special_check = 7;
    drive_end = 4;
  } else if ((drive_end == 8)
	     && (s[4] == '\\')
	     && is_drive_letter(s[5])
	     && (s[6] == ':')) {
    /* Maybe don't need \\?\\ for \\?\\C:\... */
    start_special_check = 8;
    drive_end = 5;
    drop_ss_slash = 1;
  } else if (drive_end == -2) {
    /* \\?\RED\ */
    int lit_start;
    get_slashslash_qm_dot_ups_end(s, len, &lit_start);
    start_special_check = lit_start;
    drive_end = lit_start - 1;
  } else if (drive_end < 0) {
    int lit_start, dots_end;
    dots_end = get_slashslash_qm_dot_ups_end(s, len, &lit_start);
    if (lit_start == len) {
      /* just keep the dots */
      return scheme_path_to_directory_path(scheme_make_sized_offset_kind_path(s, 8, dots_end - 8, 1, SCHEME_WINDOWS_PATH_KIND));
    }
    start_special_check = lit_start;
    if (dots_end < 9)
      drive_end = lit_start; /* no dots, so just keep the literal part */
    else {
      drive_end = 8; /* \\?\REL\..\, and we keep the .. */
      drop_extra_slash = dots_end;
      is_dir = 1;
    }
  } else if ((clean_start == 7) 
	     && ((s[4] == 'U') || (s[4] == 'u'))
	     && ((s[5] == 'N') || (s[5] == 'n'))
	     && ((s[6] == 'C') || (s[6] == 'c'))) {
    if (drive_end == len) {
      is_dir = 1;
    }
    drive_end = 6;
    start_special_check = 7; /* \\?\UNC */
    set_slash = 6;
    norm_unc = 1;
  } else if ((clean_start == 8) 
	     && (s[4] == '\\')
	     && ((s[5] == 'U') || (s[5] == 'u'))
	     && ((s[6] == 'N') || (s[6] == 'n'))
	     && ((s[7] == 'C') || (s[7] == 'c'))) {
    if (drive_end == len) {
      is_dir = 1;
    }
    drive_end = 7;
    start_special_check = 8; /* \\?\\UNC */
    set_slash = 7;
    norm_unc = 1;
    drop_ss_slash = 1;
  } else {
    /* We have a weird root. Give up. */
    found_bad = 1;
    start_special_check = len;
  }

  if (!found_bad) {
    element_start = start_special_check;
    for (i = element_start; 1; i++) {
      if ((i == len) || (s[i] == '\\')) {
	if (element_start <= i - 1) {
	  /* Need the protection? */
	  Scheme_Object *v;
	  int any_more = 0, j;
	
	  for (j = i+1; j < len; j++) {
	    if (s[j] != '\\') {
	      any_more = 1;
	      break;
	    }
	  }
	
	  v = make_protected_sized_offset_path(1, 
					       s, element_start, i - element_start,
					       1, 
					       (any_more ? 2 : 1),
                                               SCHEME_WINDOWS_PATH_KIND);
	  if (SCHEME_TRUEP(v)) {
	    found_bad = 1;
	    break;
	  }
	}
	if (i == len)
	  break;
	element_start = i + 1;
      }
    }
  }

  if (found_bad) {
    if (norm_unc) {
      if ((s[4 + drop_ss_slash] == 'U')
	  && (s[5 + drop_ss_slash] == 'N')
	  && (s[6 + drop_ss_slash] == 'C'))
	norm_unc = 0;
    }
    if (norm_unc || drop_ss_slash) {
      if (!fixed) {
	char *naya;
	naya = (char *)scheme_malloc_atomic(len);
	memcpy(naya, s, len);
	s = naya;
	fixed = 1;
      }
      if (drop_ss_slash) {
	memmove(s + 3, s + 4, len - 4);
	len--;
      }
      if (norm_unc) {
	s[4] = 'U';
	s[5] = 'N';
	s[6] = 'C';
      }
    }
    if (fixed)
      path = scheme_make_sized_offset_kind_path(s, 0, len, 1, SCHEME_WINDOWS_PATH_KIND);
    return path;
  } else {
    if (drop_extra_slash > -1) {
      char *naya;
      naya = (char *)scheme_malloc_atomic(len);
      memcpy(naya, s, drop_extra_slash);
      memcpy(naya + drop_extra_slash, s + drop_extra_slash + 1, len - drop_extra_slash - 1);
      s = naya;
      --len;
    }
    if (set_slash > -1) {
      char *naya;
      naya = (char *)scheme_malloc_atomic(len);
      memcpy(naya, s, len);
      naya[set_slash] = '\\';
      s = naya;
    }
    path = scheme_make_sized_offset_kind_path(s, drive_end, len - drive_end, 1, SCHEME_WINDOWS_PATH_KIND);
    if (is_dir)
      path = scheme_path_to_directory_path(path);
    return path;
  }
}

static Scheme_Object *do_simplify_path(Scheme_Object *path, Scheme_Object *cycle_check, int skip, 
				       int use_filesystem, 
                                       int force_rel_up,
                                       int kind, int guards)
     /* When !use_filesystem, the result can be #f for an empty relative
	path, and it can contain leading ".."s, or ".."s after an initial
        "~" path with "~" paths are absolute.
	When force_rel_up under Windows, "\\?\REL\.." from split-path is
	treated like 'up. */
{
  int isdir, cleaned_slashes = 0, must_be_dir = 0, last_was_dir = 0, did_first = 0;
  Scheme_Object *file = scheme_false, *base;

  /* cleanse-path doesn't touch the filesystem. Always start with
     that, to get things basically tidy. */
  if (kind == SCHEME_WINDOWS_PATH_KIND) {
    char *s;
    int expanded, add_sep = 0;
    s = do_expand_filename(path, SCHEME_PATH_VAL(path), SCHEME_PATH_LEN(path),
                           NULL, &expanded, 0, 0, 0, kind, 0);
    {
      int slen;
      if (expanded)
        slen = strlen(s);
      else
        slen = SCHEME_PATH_LEN(path);
      s = do_normal_path_seps(s, &slen, 0, 0, SCHEME_WINDOWS_PATH_KIND, &expanded);
    }
    if (expanded) {
      path = scheme_make_sized_offset_kind_path(s, 0, -1, 0, SCHEME_WINDOWS_PATH_KIND);
    }
    if (!check_dos_slashslash_qm(SCHEME_PATH_VAL(path), SCHEME_PATH_LEN(path), NULL, NULL, &add_sep)) {
      int len = SCHEME_PATH_LEN(path);
      s = strip_trailing_spaces(SCHEME_PATH_VAL(path), &len, 0, 0);
      if (s != SCHEME_PATH_VAL(path))
        path = scheme_make_sized_offset_kind_path(s, 0, -1, 0, SCHEME_WINDOWS_PATH_KIND);
    } else if (add_sep) {
      int len = SCHEME_PATH_LEN(path);
      if ((add_sep < len) && (s[add_sep] != '\\')) {
        /* Add two \, as in \\?\c -> \\?\\\c */
        char *naya;
        naya = (char *)scheme_malloc_atomic(len + 3);
        memcpy(naya, s, add_sep);
        naya[add_sep] = '\\';
        naya[add_sep+1] = '\\';
        memcpy(naya + add_sep + 2, s + add_sep, len + 1 - add_sep);
        len += 2;
        path = scheme_make_sized_offset_kind_path(naya, 0, len, 0, SCHEME_WINDOWS_PATH_KIND);
      } else if (((add_sep + 1) < len) && (s[add_sep] == '\\') && (s[add_sep+1] != '\\')) {
        /* Add \, as in \\?\\c -> \\?\\\c */
        char *naya;
        naya = (char *)scheme_malloc_atomic(len + 2);
        memcpy(naya, s, add_sep);
        naya[add_sep] = '\\';
        memcpy(naya + add_sep + 1, s + add_sep, len + 1 - add_sep);
        len++;
        path = scheme_make_sized_offset_kind_path(naya, 0, len, 0, SCHEME_WINDOWS_PATH_KIND);
      }
    }
  }

  /* Fast check; avoids split operations, if possible.
     Also responsible for determining whether there's a
     redundant or missing trailing slash in the case that
     the path is just a root. */
  {
    char *s;
    int len, i, saw_dot = 0;
    s = SCHEME_PATH_VAL(path);
    len = SCHEME_PATH_LEN(path);

    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      if (!skip && check_dos_slashslash_qm(s, len, NULL, NULL, NULL)) {
        if (!force_rel_up) {
	  int drive_end;
          path = simplify_qm_path(path);
	  len = SCHEME_PATH_LEN(path);
	  if (check_dos_slashslash_qm(SCHEME_PATH_VAL(path), len, &drive_end, NULL, NULL)) {
	    /* If it's a drive... */
	    if (drive_end == len) {
	      /* Make it a directory path. */
	      path = scheme_path_to_directory_path(path);
	    }
	  }
	  return path;
        } else {
	  /* force_rel_up means that we want a directory: */
          return scheme_path_to_directory_path(path);
	}
      }
      if (!skip && check_dos_slashslash_drive(s, 0, len, NULL, 1, 0)) {
        /* A UNC drive (with no further elements). 
	   Remove extra trailing slashes, if any... */
        for (i = len; IS_A_DOS_SEP(s[i-1]); i--) { }
        if (i < len - 1) {
          path = scheme_make_sized_offset_kind_path(s, 0, i, 1, SCHEME_WINDOWS_PATH_KIND);
        }
	/* ... but make it a directory path. */
        path = scheme_path_to_directory_path(path);
      }

      if (skip) {
        while (s[skip] == '\\') {
          skip++;
        }
      }
    }

    i = skip;
    if (kind == SCHEME_WINDOWS_PATH_KIND) {
      if (!i && (len >= 2) && is_drive_letter(s[0]) && s[1] == ':') {
        i = 2;
      } else if (!i) {
        int drive_end;
        if (check_dos_slashslash_drive(s, 0, len, &drive_end, 0, 0)) {
          i = drive_end;
        }
      }
    }

    for (; i < len; i++) {
      if (s[i] == '.')
	saw_dot++;
      else if (IS_A_SEP(kind, s[i])) {
	if ((saw_dot == 1) || (saw_dot == 2))
	  break;
        if ((i + 1 < len) && (IS_A_SEP(kind, s[i]))) {
          /* Double slash to clean up... */
          break;
        }
	saw_dot = 0;
      } else
	saw_dot = 3;
    }

    if (i == len) {
      if ((saw_dot != 1) && (saw_dot != 2)) {
        /* Still may need to add trailing separator if it's syntactically a directory. */
        if (path_is_simple_dir_without_sep(path))
          path = scheme_path_to_directory_path(path);
        return path;
      }
    }
    /* There's a ., .., or // in the path... */
  }

  /* Check whether it can be simplified: */
  if (!cleaned_slashes) {
    base = path;
    do {
      char *s;
      int len;
      s = SCHEME_PATH_VAL(base);
      len = SCHEME_PATH_LEN(base);
      if (len <= skip)
        break;
      file = do_split_path_once(s, len, &base, &isdir, &cleaned_slashes, kind);
      if (kind == SCHEME_WINDOWS_PATH_KIND) {
        if (force_rel_up) {
          file = convert_literal_relative(file);
        }
      }
      if (SCHEME_SYMBOLP(file) || cleaned_slashes)
        break;
    } while (SCHEME_GENERAL_PATHP(base));
  } else
    file = scheme_false;

  if (SCHEME_SYMBOLP(file) || cleaned_slashes) {
    /* It can be simplified: */
    char *s;
    int len;
    Scheme_Object *accum = scheme_null, *result;

    s = SCHEME_PATH_VAL(path);
    len = SCHEME_PATH_LEN(path);

    if (use_filesystem
	&& !scheme_is_complete_path(s, len, kind)) {
      /* Make it absolute */
      s = scheme_expand_string_filename(path,
					"simplify-path", NULL,
					guards ? SCHEME_GUARD_FILE_EXISTS : 0);
      len = strlen(s);
    }

    /* Check for cycles: */
    if (use_filesystem) {
      {
	Scheme_Object *l = cycle_check;
	while (!SCHEME_NULLP(l)) {
	  Scheme_Object *p = SCHEME_CAR(l);
	  if ((len == SCHEME_PATH_LEN(p))
	      && !strcmp(s, SCHEME_PATH_VAL(p))) {
	    /* Cycle of links detected */
	    scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
			     "simplify-path: cycle detected at link\n"
                             "  link path: %q",
			     s);
	  }
	  l = SCHEME_CDR(l);
	}
      }
    
      cycle_check = scheme_make_pair(scheme_make_sized_path(s, len, 0), 
				     cycle_check);
    }

    /* Split the path into a list. */
    while (1) {
      if (len <= skip) {
	accum = scheme_make_pair(scheme_make_sized_offset_kind_path(s, 0, len, 0, kind), accum);
	break;
      }

      file = scheme_split_path(s, len, &base, &isdir, kind);
      if (kind == SCHEME_WINDOWS_PATH_KIND) {
        if (force_rel_up) {
          file = convert_literal_relative(file);
          if (SCHEME_SYMBOLP(file))
            isdir = 1;
        }
      }

      if (!did_first) {
        must_be_dir = isdir;
        did_first = 1;
      }

      if (SAME_OBJ(file, same_symbol)) {
	/* Drop it */
      } else
	accum = scheme_make_pair(file, accum);
      
      if (SCHEME_GENERAL_PATHP(base)) {
	s = SCHEME_PATH_VAL(base);
	len = SCHEME_PATH_LEN(base);
      } else {
	if (use_filesystem) {
	  accum = scheme_make_pair(file, SCHEME_CDR(accum));
	}
	break;
      }
    }

    /* Now assemble the result */
    if (SCHEME_NULLP(accum)) {
      /* Only happens when !use_filesystem */
      result = scheme_false;
    } else {
      result = SCHEME_CAR(accum);
      if (SAME_OBJ(result, up_symbol)) {
	/* Only happens when !use_filesystem */
	result = scheme_false;
      } else
	accum = SCHEME_CDR(accum);
    }

    /* Build up path, watching for links just before a ..: */
    while (!SCHEME_NULLP(accum)) {
      if (SAME_OBJ(SCHEME_CAR(accum), up_symbol)) {
	if (use_filesystem && (SCHEME_PLATFORM_PATH_KIND != SCHEME_WINDOWS_PATH_KIND)) {
	  /* Look for symlink in result-so-far. */
	  Scheme_Object *new_result, *a[1];

	  while (1) {
	    a[0] = result;
	    new_result = do_resolve_path(1, a, guards);
	
	    /* Was it a link? */
	    if (result != new_result) {
	      /* It was a link. Is the new result relative? */
	      if (!scheme_is_complete_path(SCHEME_PATH_VAL(new_result),
					   SCHEME_PATH_LEN(new_result),
                                           kind)) {
		Scheme_Object *aa[2], *result_base;
		/* Yes - resolve it relative to result's base: */
		scheme_split_path(SCHEME_PATH_VAL(result),
				  SCHEME_PATH_LEN(result),
				  &result_base,
				  &isdir,
                                  kind);
		aa[0] = result_base;
		aa[1] = new_result;
		new_result = do_build_path(2, aa, 0, 0, SCHEME_PLATFORM_PATH_KIND);
	      }

	      {
		Scheme_Object *cl, *cp;
		for (cl = cycle_check; !SCHEME_NULLP(cl); cl = SCHEME_CDR(cl)) {
		  cp = SCHEME_CAR(cl);
		  if ((SCHEME_PATH_LEN(cp) == SCHEME_PATH_LEN(new_result))
		      && !strcmp(SCHEME_PATH_VAL(cp), SCHEME_PATH_VAL(new_result))) {
		    /* cycle */
		    new_result = NULL;
		    break;
		  }
		}
	      }
	    
	      if (new_result) {
		/* Simplify the new result */
		result = do_simplify_path(new_result, cycle_check, skip,
					  use_filesystem, force_rel_up, kind,
					  guards);
		cycle_check = scheme_make_pair(new_result, cycle_check);
	      } else
		break;
	    } else
	      break;
	  }
	}
	
	/* Do one 'up: */
	{
	  accum = SCHEME_CDR(accum);
	  if (SCHEME_FALSEP(result)) {
	    /* Empty relative path so far */
	    if (skip) /* => input was a \\?\ path, and it must be relative */
	      result = scheme_make_sized_offset_kind_path("\\\\?\\REL\\..", 0, 10, 0, SCHEME_WINDOWS_PATH_KIND);
	    else
	      result = scheme_make_sized_offset_kind_path("..", 0, 2, 0, kind);
	  } else {
	    Scheme_Object *next, *to_go;
	    to_go = scheme_split_path(SCHEME_PATH_VAL(result),
				      SCHEME_PATH_LEN(result),
				      &next,
				      &isdir,
                                      kind);
	    if (SAME_OBJ(to_go, up_symbol)) {
	      /* We're building a sequence of ups... */
	      Scheme_Object *a[2];
	      a[0] = result;
	      a[1] = up_symbol;
	      result = do_build_path(2, a, 0, 1, kind);
#ifdef TILDE_IS_ABSOLUTE
	    } else if ((kind == SCHEME_UNIX_PATH_KIND)
                       && SCHEME_FALSEP(next)
                       && SCHEME_GENERAL_PATHP(to_go)
                       && SCHEME_PATH_VAL(to_go)[0] == '~') {
	      /* Can't delete a leading ~ for .. */
	      Scheme_Object *a[2];
	      a[0] = result;
	      a[1] = up_symbol;
	      result = do_build_path(2, a, 0, 1, kind);
#endif
	    } else if (!SCHEME_GENERAL_PATH_STRINGP(next)) {
	      if (SCHEME_FALSEP(next)) {
		/* Result is already a root, so we just drop the .. */
	      } else {
		/* Result is empty relative path */
		result = scheme_false;
	      }
	    } else
	      result = next;
	  }
	}

        last_was_dir = 1;
      } else {
	/* Add path element onto the result: */
	if (SCHEME_FALSEP(result))
	  result = SCHEME_CAR(accum);
	else {
	  Scheme_Object *a[2];
	  a[0] = result;
	  a[1] = SCHEME_CAR(accum);
	  result = do_build_path(2, a, 0, 0, kind);
	}
	accum = SCHEME_CDR(accum);
        last_was_dir = 0;
      }
    }

    if ((must_be_dir || last_was_dir) && !SCHEME_FALSEP(result)) {
      result = scheme_path_to_directory_path(result);
    }

    return result;
  } else
    return path;
}

Scheme_Object *scheme_simplify_path(int argc, Scheme_Object *argv[])
{
  char *s;
  int len, use_fs, kind;
  Scheme_Object *bs, *r;

  if (!SCHEME_GENERAL_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("simplify-path", "(or/c path-for-some-system? path-string?)", 0, argc, argv);

  bs = TO_PATH(argv[0]);

  s = SCHEME_PATH_VAL(bs);
  len = SCHEME_PATH_LEN(bs);

  if (has_null(s, len))
    raise_null_error("simplify-path", argv[0], "");

  use_fs = ((argc <= 1) || SCHEME_TRUEP(argv[1]));
  kind = SCHEME_PATH_KIND(bs);

  if (use_fs && (kind != SCHEME_PLATFORM_PATH_KIND)) {
    scheme_contract_error("simplify-path",
                          "in use-filesystem mode, path is not for the current platform",
                          "path", 1, argv[0],
                          NULL);
  }
  
  r = do_simplify_path(bs, scheme_null, 0, use_fs, 0, kind, 1);

  if (SCHEME_FALSEP(r)) {
    /* Input was just 'same: */
    return scheme_make_sized_offset_kind_path((kind == SCHEME_WINDOWS_PATH_KIND) ? ".\\" : "./", 0, 2, 0, kind);
  }

  return r;
}

static Scheme_Object *current_drive(int argc, Scheme_Object *argv[])
{
#ifdef DOS_FILE_SYSTEM
  char *drive;

  drive = scheme_getdrive();

  return scheme_make_sized_path(drive, strlen(drive), 0);
#else
  scheme_raise_exn(MZEXN_FAIL_UNSUPPORTED, "current-drive: " NOT_SUPPORTED_STR);
  return NULL;
#endif
}

static Scheme_Object *cleanse_path(int argc, Scheme_Object *argv[])
{
  char *filename;
  int expanded, kind;

  if (!SCHEME_GENERAL_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("cleanse-path", "(or/c path-for-some-system? path-string?)", 0, argc, argv);

  if (SCHEME_GENERAL_PATHP(argv[0]))
    kind = SCHEME_PATH_KIND(argv[0]);
  else
    kind = SCHEME_PLATFORM_PATH_KIND;

  filename = do_expand_filename(argv[0],
				NULL,
				0,
				"cleanse-path",
				&expanded,
				1, 0,
				0, /* no security check, since the filesystem is not used */ 
                                kind,
                                0);
  
  if (!expanded && SCHEME_GENERAL_PATHP(argv[0]))
    return argv[0];
  else
    return scheme_make_sized_offset_kind_path(filename, 0, strlen(filename), 1, kind);
}

static Scheme_Object *expand_user_path(int argc, Scheme_Object *argv[])
{
  char *filename;
  int expanded;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("expand-user-path", "path-string?", 0, argc, argv);

  filename = do_expand_filename(argv[0],
				NULL,
				0,
				"expand-user-path",
				&expanded,
				1, 0,
				SCHEME_GUARD_FILE_EXISTS,
                                SCHEME_PLATFORM_PATH_KIND,
                                1);

  if (!expanded && SCHEME_PATHP(argv[0]))
    return argv[0];
  else
    return scheme_make_sized_path(filename, strlen(filename), 1);
}

static void escape_during_directory_list(rktio_directory_list_t *dl)
{
  rktio_directory_list_stop(scheme_rktio, dl);
}

static Scheme_Object *do_directory_list(int break_ok, int argc, Scheme_Object *argv[])
{
  char *filename;
  Scheme_Object *first = scheme_null, *last = NULL, *n, *elem;
  int counter = 0;
  rktio_directory_list_t *dl;
  char *s;

  if (argc && !SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("directory-list", "path-string?", 0, argc, argv);

  if (argc) {
    Scheme_Object *path = argv[0];
# ifdef DOS_FILE_SYSTEM
    while (1) {
# endif
      filename = do_expand_filename(path, NULL, 0, 
				    break_ok ? "directory-list" : NULL, 
				    NULL, 1, 259 - 4 /* leave room for \*.* in Windows */, 
				    break_ok ? SCHEME_GUARD_FILE_READ : 0, 
                                    SCHEME_PLATFORM_PATH_KIND,
                                    0);
      if (!filename)
	return NULL;
# ifdef DOS_FILE_SYSTEM
      /* Eliminate "." and "..": */
      if (SAME_OBJ(path, argv[0])) {
	Scheme_Object *old;
	old = scheme_make_path(filename);
	path = do_simplify_path(old, scheme_null, 0, 1, 0, SCHEME_WINDOWS_PATH_KIND, break_ok);
	if (SAME_OBJ(path, old))
	  break;
      } else
	break;
    }
# endif
  } else {
    filename = SCHEME_PATH_VAL(CURRENT_WD());
    if (break_ok) {
      scheme_security_check_file("directory-list", NULL, SCHEME_GUARD_FILE_EXISTS);
      scheme_security_check_file("directory-list", filename, SCHEME_GUARD_FILE_READ);
    }
  }

  dl = rktio_directory_list_start(scheme_rktio, filename);
  if (!dl) {
    if (break_ok)
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                       "directory-list: could not open directory\n"
                       "  path: %q\n"
                       "  system error: %R",
                       filename);
    return NULL;
  }

  do {
    s = rktio_directory_list_step(scheme_rktio, dl);
    if (!*s)
      break;

    n = make_protected_sized_offset_path(1, s, 0, strlen(s), 1, 0, SCHEME_PLATFORM_PATH_KIND);
    elem = scheme_make_pair(n, scheme_null);
    if (last)
      SCHEME_CDR(last) = elem;
    else
      first = elem;
    last = elem;

    counter++;
    if (break_ok && !(counter & 0xF)) {
      BEGIN_ESCAPEABLE(escape_during_directory_list, dl);
      SCHEME_USE_FUEL(1);
      END_ESCAPEABLE();
    }
  } while (1);

  return first;
}

static Scheme_Object *directory_list(int argc, Scheme_Object *argv[])
{
  return do_directory_list(1, argc, argv);
}

char *scheme_find_completion(char *fn)
{
  int len;
  Scheme_Object *p, *l, *a[2], *f, *matches, *fst;
  int isdir, max_match;
  Scheme_Object *base;
  
  len = strlen(fn);

  if (!len)
    return NULL;
  
  f = scheme_split_path(fn, len, &base, &isdir, SCHEME_PLATFORM_PATH_KIND);
  if (isdir) {
    /* Look for single file/prefix in directory: */
    base = scheme_make_sized_path(fn, len, 0);
    f = scheme_make_sized_path("", 0, 0);
  } else {
    if (!SCHEME_PATHP(base))
      return NULL;
  }

  a[0] = base;
  l = do_directory_list(0, 1, a);
  if (!l)
    return NULL;

  matches = scheme_null;
  while (SCHEME_PAIRP(l)) {
    p = SCHEME_CAR(l);
    if ((SCHEME_PATH_LEN(p) >= SCHEME_PATH_LEN(f))
	&& !memcmp(SCHEME_PATH_VAL(f), SCHEME_PATH_VAL(p), SCHEME_PATH_LEN(f))) {
      matches = scheme_make_pair(p, matches);
    }
    l = SCHEME_CDR(l);
  }

  if (SCHEME_NULLP(matches))
    return NULL;

  if (SCHEME_NULLP(SCHEME_CDR(matches))) {
    /* One match */
    a[0] = base;
    a[1] = SCHEME_CAR(matches);
    p = scheme_build_path(2, a);
    a[0] = p;
    if (SCHEME_TRUEP(directory_exists(1, a))) {
      /* Add trailing separator if one is not there */
      fn = SCHEME_PATH_VAL(p);
      len = SCHEME_PATH_LEN(p);
      if (!IS_A_SEP(SCHEME_PLATFORM_PATH_KIND, fn[len-1])) {
	char *naya;
	naya = (char *)scheme_malloc_atomic(len + 2);
	memcpy(naya, fn, len);
	naya[len++] = FN_SEP(SCHEME_PLATFORM_PATH_KIND);
	naya[len] = 0;
	fn = naya;
      }
    } else
      fn = SCHEME_PATH_VAL(p);
    return fn;
  }

  fst = SCHEME_CAR(matches);
  max_match = SCHEME_PATH_LEN(fst);
  for (l = SCHEME_CDR(matches); SCHEME_PAIRP(l); l = SCHEME_CDR(l)) {
    int i, l2;
    p = SCHEME_CAR(l);
    l2 = SCHEME_PATH_LEN(p);
    if (max_match < l2)
      l2 = max_match;
    else if (l2 < max_match)
      max_match = l2;
    for (i = 0; i < l2; i++) {
      if (SCHEME_PATH_VAL(fst)[i] != SCHEME_PATH_VAL(p)[i]) {
	max_match = i;
	break;
      }
    }
  }

  if (max_match <= SCHEME_PATH_LEN(f)) 
    /* No longer match available: */
    return NULL;

  /* Build match */
  a[0] = base;
  a[1] = scheme_make_sized_path(SCHEME_PATH_VAL(fst), max_match, 0);
  f = scheme_build_path(2, a);  

  return SCHEME_PATH_VAL(f);
}

static Scheme_Object *do_explode_path(Scheme_Object *p)
{
  return explode_path(1, &p);
}

static Scheme_Object *to_bytes(Scheme_Object *p)
{
  if (SCHEME_PATHP(p))
    return scheme_make_sized_byte_string(SCHEME_PATH_VAL(p),
                                         SCHEME_PATH_LEN(p),
                                         1);
  else
    return p;
}

Scheme_Object *scheme_extract_relative_to(Scheme_Object *obj, Scheme_Object *dir, Scheme_Hash_Table *cache)
/* When cache is non-NULL, generate a path or a list of byte strings (suitable for bytecode) */
{
  Scheme_Object *de, *be, *oe, *orig_obj = obj;

  if (cache) {
    de = scheme_hash_get(cache, obj);
    if (de)
      return de;
  }

  if (SCHEME_PAIRP(dir)) {
    be = do_explode_path(SCHEME_CAR(dir));
    de = do_explode_path(SCHEME_CDR(dir));
  } else {
    be = do_explode_path(dir);
    de = be;
  }
  oe = do_explode_path(obj);

  while (SCHEME_PAIRP(de)
	 && SCHEME_PAIRP(oe)) {
    if (!scheme_equal(SCHEME_CAR(de), SCHEME_CAR(oe)))
      return obj;
    de = SCHEME_CDR(de);
    oe = SCHEME_CDR(oe);
    be = SCHEME_CDR(be);
  }

  if (SCHEME_NULLP(de)) {
    Scheme_Object *a[2];

    while (SCHEME_PAIRP(be)
           && SCHEME_PAIRP(oe)
           && scheme_equal(SCHEME_CAR(be), SCHEME_CAR(oe))) {
      oe = SCHEME_CDR(oe);
      be = SCHEME_CDR(be);
    }

    /* If cache is non-NULL, generate a list of byte strings */

    if (SCHEME_NULLP(oe)) {
      if (cache) {
        obj = scheme_null;
      } else {
        a[0] = same_symbol;
        obj = scheme_build_path(1, a);
      }
    } else {
      obj = SCHEME_CAR(oe);
      if (cache)
        obj = scheme_make_pair(to_bytes(obj), scheme_null);
      oe = SCHEME_CDR(oe);
    }

    while (SCHEME_PAIRP(oe)) {
      if (cache) {
        obj = scheme_make_pair(to_bytes(SCHEME_CAR(oe)), obj);
      } else {
        a[0] = obj;
        a[1] = SCHEME_CAR(oe);
        obj = scheme_build_path(2, a);
      }
      oe = SCHEME_CDR(oe);
    }

    if (cache)
      obj = scheme_reverse(obj);

    while (!SCHEME_NULLP(be)) {
      if (cache) {
        obj = scheme_make_pair(up_symbol, obj);
      } else {
        a[0] = up_symbol;
        a[1] = obj;
        obj = scheme_build_path(2, a);
      }
      be = SCHEME_CDR(be);
    }
  }

  if (cache)
    scheme_hash_set(cache, orig_obj, obj);

  return obj;
}

Scheme_Object *scheme_maybe_build_path(Scheme_Object *base, Scheme_Object *elem)
{
  Scheme_Object *a[2];
  
  if (!base)
    base = scheme_get_param(scheme_current_config(), MZCONFIG_CURRENT_DIRECTORY);

  if (SAME_OBJ(elem, same_symbol)
      || SAME_OBJ(elem, up_symbol)) {
    /* ok */
  } else if (SCHEME_BYTE_STRINGP(elem)) {
    a[0] = elem;
    elem = bytes_to_path_element(1, a);
  } else
    elem = NULL;

  if (elem) {
    a[0] = base;
    a[1] = elem;
    return scheme_build_path(2, a);
  } else
    return base;
}

static Scheme_Object *filesystem_root_list(int argc, Scheme_Object *argv[])
{
  Scheme_Object *first = scheme_null;
  Scheme_Object *last = NULL, *v;
  char **roots;
  int i;
  
  scheme_security_check_file("filesystem-root-list", NULL, SCHEME_GUARD_FILE_EXISTS);

  roots = rktio_filesystem_roots(scheme_rktio);
  for (i = 0; roots[i]; i++) {
    v = scheme_make_pair(scheme_make_sized_offset_path(roots[i], 0, -1, 1), scheme_null);
    if (last)
      SCHEME_CDR(last) = v;
    else
      first = v;
    last = v;
    free(roots[i]);
  }

  free(roots);

  return first;
}

static Scheme_Object *make_directory(int argc, Scheme_Object *argv[])
{
  char *filename;
  int copied;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("make-directory", "path-string?", 0, argc, argv);

  filename = scheme_expand_string_filename(argv[0],
					   "make-directory",
					   &copied,
					   SCHEME_GUARD_FILE_WRITE);

  if (!rktio_make_directory(scheme_rktio, filename)) {
    if (scheme_last_error_is_racket(RKTIO_ERROR_EXISTS)) {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM_EXISTS,
                       "make-directory: cannot make directory;\n"
                       " the path already exists\n"
                       "  path: %q",
                       filename_for_error(argv[0]));
    } else {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                       "make-directory: cannot make directory\n"
                       "  path: %q\n"
                       "  system error: %R",
                       filename_for_error(argv[0]));
    }
  }
  
  return scheme_void;
}

static Scheme_Object *delete_directory(int argc, Scheme_Object *argv[])
{
  char *filename;
  char *current_directory;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("delete-directory", "path-string?", 0, argc, argv);

  filename = scheme_expand_string_filename(argv[0],
					   "delete-directory",
					   NULL,
					   SCHEME_GUARD_FILE_DELETE);

#ifdef DOS_FILE_SYSTEM
  {
    Scheme_Object *tcd;
    tcd = scheme_get_param(scheme_current_config(), MZCONFIG_CURRENT_DIRECTORY);
    current_directory = SCHEME_PATH_VAL(tcd);
  }
#else
  current_directory = NULL;
#endif
  
  if (!rktio_delete_directory(scheme_rktio, filename, current_directory,
                              scheme_can_enable_write_permission())) {
    scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                     "delete-directory: cannot delete directory\n"
                     "  path: %q\n"
                     "  system error: %R",
                     filename_for_error(argv[0]));
  }

  return scheme_void;
}

static Scheme_Object *make_link(int argc, Scheme_Object *argv[])
{
  char *src;
  Scheme_Object *dest;
  int dest_is_dir, copied;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("make-file-or-directory-link", "path-string?", 0, argc, argv);
  if (!SCHEME_PATH_STRINGP(argv[1]))
    scheme_wrong_contract("make-file-or-directory-link", "path-string?", 0, argc, argv);

  dest = argv[0];
  /* dest does not get expanded, but we need to make sure it's a path */
  dest = TO_PATH(dest);
  if (has_null(SCHEME_PATH_VAL(dest), SCHEME_PATH_LEN(dest))) {
    raise_null_error("make-file-or-directory-link", dest, "");
    return NULL;
  }

  src = scheme_expand_string_filename(argv[1],
				      "make-file-or-directory-link",
				      &copied,
				      SCHEME_GUARD_FILE_WRITE);

  scheme_security_check_file_link("make-file-or-directory-link", 
				  src, 
				  SCHEME_PATH_VAL(dest));


#if defined(DOS_FILE_SYSTEM)
  if (do_path_to_directory_path(src, 0, -1, argv[1], 1, SCHEME_WINDOWS_PATH_KIND))
	dest_is_dir = 1;
  else
	dest_is_dir = 0;
#else
  dest_is_dir = 0;
#endif

  if (!rktio_make_link(scheme_rktio, src, SCHEME_PATH_VAL(dest), dest_is_dir)) {
    if (scheme_last_error_is_racket(RKTIO_ERROR_EXISTS)) {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM_EXISTS,
                       "make-file-or-directory-link: cannot make link;\n"
                       " the path already exists\n"
                       "  path: %q",
                       filename_for_error(argv[0]));
    } else {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                       "make-file-or-directory-link: cannot make link\n"
                       "  path: %q\n"
                       "  system error: %R",
                       filename_for_error(argv[0]));
    }
  }

  return scheme_void;
}

static Scheme_Object *file_modify_seconds(int argc, Scheme_Object **argv)
{
  char *file;
  int set_time = 0;
  UNBUNDLE_TIME_TYPE mtime;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("file-or-directory-modify-seconds", "path-string?", 0, argc, argv);

  set_time = ((argc > 1) && SCHEME_TRUEP(argv[1]));

  file = scheme_expand_string_filename(argv[0],
				       "file-or-directory-modify-seconds",
				       NULL,
				       (set_time
					? SCHEME_GUARD_FILE_WRITE
					: SCHEME_GUARD_FILE_READ));
  
  if (set_time) {
    if (!SCHEME_INTP(argv[1]) && !SCHEME_BIGNUMP(argv[1])) {
      scheme_wrong_contract("file-or-directory-modify-seconds", "(or/c exact-integer? #f)", 1, argc, argv);
      return NULL;
    }
    if (!scheme_get_time_val(argv[1], &mtime)) {
      scheme_contract_error("file-or-directory-modify-seconds",
                            "integer value is out-of-range",
                            "value", 1, argv[1],
                            NULL);
      return NULL;
    }
  } else
    mtime = 0;

  if (argc > 2) {
    scheme_check_proc_arity("file-or-directory-modify-seconds", 0, 2, argc, argv);
  }

  if (!set_time) {
    rktio_timestamp_t *ts;

    ts = rktio_get_file_modify_seconds(scheme_rktio, file);

    if (ts) {
      intptr_t ts_v = *ts;
      free(ts);
      return scheme_make_integer_value_from_time(ts_v);
    }
  } else {
    if (rktio_set_file_modify_seconds(scheme_rktio, file, mtime))
      return scheme_void;
  }

  if (argc > 2) {
    return _scheme_tail_apply(argv[2], 0, NULL);
  }

  scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
		   "file-or-directory-modify-seconds: error %s file/directory time\n"
                   "  path: %q\n"
                   "  system error: %R",
		   set_time ? "setting" : "getting",
		   filename_for_error(argv[0]));

  return NULL;
}

static Scheme_Object *file_or_dir_permissions(int argc, Scheme_Object *argv[])
{
  Scheme_Object *l = scheme_null;
  char *filename;
  int as_bits = 0, set_bits = 0, new_bits = 0;
  int r = 0;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("file-or-directory-permissions", "path-string?", 0, argc, argv);
  if (argc > 1) {
    l = argv[1];
    if (SCHEME_FALSEP(l)) {
    } else if (SCHEME_SYMBOLP(l) && !SCHEME_SYM_WEIRDP(l)
        && !strcmp("bits", SCHEME_SYM_VAL(l))) {
      as_bits = 1;
    } else {
      as_bits = -1;
      l = argv[1];
      if (SCHEME_INTP(l) 
          && (SCHEME_INT_VAL(l) >= 0) 
          && (SCHEME_INT_VAL(l) <= 0xFFFF)) {
        set_bits = 1;
        new_bits = SCHEME_INT_VAL(l);
      } else
        scheme_wrong_contract("file-or-directory-permissions", 
                              "(or/c #f 'bits (integer-in 0 65535))",
                              1, argc, argv);
    }
  }

  filename = scheme_expand_string_filename(argv[0],
					   "file-or-directory-permissions",
					   NULL,
					   (set_bits
                                            ? SCHEME_GUARD_FILE_WRITE
                                            : SCHEME_GUARD_FILE_READ));

  if (!set_bits) {
    r = rktio_get_file_or_directory_permissions(scheme_rktio, filename, as_bits);
    if (r != RKTIO_PERMISSION_ERROR) {
      if (as_bits)
        return scheme_make_integer(r);
      else {
        if (r & RKTIO_PERMISSION_READ)
          l = scheme_make_pair(read_symbol, l);
        if (r & RKTIO_PERMISSION_WRITE)
          l = scheme_make_pair(write_symbol, l);
        if (r & RKTIO_PERMISSION_EXEC)
          l = scheme_make_pair(execute_symbol, l);
        return l;
      }
    }
  } else {
    if (rktio_set_file_or_directory_permissions(scheme_rktio, filename, new_bits))
      return scheme_void;

    if (scheme_last_error_is_racket(RKTIO_ERROR_BAD_PERMISSION)) {
      scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                       "file-or-directory-permissions: update failed due to"
                       " unsupported bit combination\n"
                       "  path: %s\n"
                       "  permission value: %d",
                       filename_for_error(argv[0]),
                       new_bits);
    }
  }
  
  scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
                   "file-or-directory-permissions: %s failed\n"
                   "  path: %q\n"
                   "  system error: %R",
                   set_bits ? "update" : "access",
                   filename_for_error(argv[0]));

  return NULL;
}

static Scheme_Object *file_identity(int argc, Scheme_Object *argv[])
{
  char *filename;
  int as_link = 0;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("file-or-directory-identity", "path-string?", 0, argc, argv);

  filename = scheme_expand_string_filename(argv[0],
					   "file-or-directory-identity",
					   NULL,
					   SCHEME_GUARD_FILE_EXISTS);

  if (argc > 1)
    as_link = SCHEME_TRUEP(argv[1]);

  return scheme_get_fd_identity(NULL, as_link, filename, 0);
}

static Scheme_Object *file_size(int argc, Scheme_Object *argv[])
{
  rktio_filesize_t *sz;
  char *filename;

  if (!SCHEME_PATH_STRINGP(argv[0]))
    scheme_wrong_contract("file-size", "path-string?", 0, argc, argv);

  filename = scheme_expand_string_filename(argv[0],
					   "file-size",
					   NULL,
					   SCHEME_GUARD_FILE_READ);

  sz = rktio_file_size(scheme_rktio, filename);
  if (sz) {
    mzlonglong szv = *sz;
    free(sz);
    return scheme_make_integer_value_from_long_long(szv);
  }

  scheme_raise_exn(MZEXN_FAIL_FILESYSTEM,
		   "file-size: cannot get size\n"
                   "  path: %q\n"
                   "  system error: %R",
		   filename_for_error(argv[0]));
  
  return NULL;
}

static Scheme_Object *cwd_check(int argc, Scheme_Object **argv)
{
  if (!SCHEME_PATH_STRINGP(argv[0])) {
    return NULL;
  } else {
    char *expanded;
    Scheme_Object *ed;

    expanded = scheme_expand_string_filename(argv[0], "current-directory", NULL, SCHEME_GUARD_FILE_EXISTS);
    ed = scheme_make_sized_path(expanded, strlen(expanded), 1);

    ed = do_simplify_path(ed, scheme_null, 0, 1, 0, SCHEME_PLATFORM_PATH_KIND, 1);

    ed = scheme_path_to_directory_path(ed);

    return ed;
  }
}

static Scheme_Object *current_directory(int argc, Scheme_Object **argv)
{
  if (!argc)
    scheme_security_check_file("current-directory", NULL, SCHEME_GUARD_FILE_EXISTS);

  return scheme_param_config2("current-directory",
                              scheme_make_integer(MZCONFIG_CURRENT_DIRECTORY),
                              argc, argv,
                              -1, cwd_check, 
                              "path-string?", 1);
}

static Scheme_Object *current_user_directory(int argc, Scheme_Object **argv)
{
  if (!argc)
    scheme_security_check_file("current-directory-for-user", NULL, SCHEME_GUARD_FILE_EXISTS);

  return scheme_param_config2("current-directory-for-user",
                              scheme_make_integer(MZCONFIG_CURRENT_USER_DIRECTORY),
                              argc, argv,
                              -1, cwd_check, 
                              "path-string?", 1);
}

static Scheme_Object *current_force_delete_perms(int argc, Scheme_Object *argv[])
{
  return scheme_param_config("current-force-delete-permissions",
                             scheme_make_integer(MZCONFIG_FORCE_DELETE_PERMS),
                             argc, argv, -1, NULL, NULL, 1);
}

/********************************************************************************/

Scheme_Object *scheme_get_run_cmd(void)
{
  if (!run_cmd) {
    return scheme_make_path("racket");
  }
  return run_cmd;
}

static Scheme_Object *
find_system_path(int argc, Scheme_Object **argv)
{
  int which;
  int should_be_dir = 1;

  if (argv[0] == temp_dir_symbol)
    which = RKTIO_PATH_TEMP_DIR;
  else if (argv[0] == home_dir_symbol)
    which = RKTIO_PATH_HOME_DIR;
  else if (argv[0] == doc_dir_symbol)
    which = RKTIO_PATH_DOC_DIR;
  else if (argv[0] == desk_dir_symbol)
    which = RKTIO_PATH_DESK_DIR;
  else if (argv[0] == pref_dir_symbol)
    which = RKTIO_PATH_PREF_DIR;
  else if (argv[0] == init_dir_symbol)
    which = RKTIO_PATH_INIT_DIR;
  else if (argv[0] == pref_file_symbol) {
    which = RKTIO_PATH_PREF_FILE;
    should_be_dir = 0;
  } else if (argv[0] == init_file_symbol) {
    which = RKTIO_PATH_INIT_FILE;
    should_be_dir = 0;
  } else if (argv[0] == sys_dir_symbol)
    which = RKTIO_PATH_SYS_DIR;
  else if (argv[0] == exec_file_symbol) {
    if (!exec_cmd) {
       return scheme_make_path("racket");
    }
    return exec_cmd;
  } else if (argv[0] == run_file_symbol) {
    return scheme_get_run_cmd();
  } else if ((argv[0] == host_collects_dir_symbol) && host_collects_path)
    return host_collects_path;
  else if ((argv[0] == collects_dir_symbol) || (argv[0] == host_collects_dir_symbol)) {
    if (!collects_path) {
      return scheme_make_path("collects");
    }
    return collects_path;
  } else if ((argv[0] == host_config_dir_symbol) && host_config_path)
    return host_config_path;
  else if ((argv[0] == config_dir_symbol) || (argv[0] == host_config_dir_symbol)) {
    if (!config_path) {
      return scheme_make_path("lib");
    }
    return config_path;
  } else if (argv[0] == orig_dir_symbol) {
    return original_pwd;
  } else if (argv[0] == addon_dir_symbol) {
    if (addon_dir) return addon_dir;
    which = RKTIO_PATH_ADDON_DIR;
  } else {
    scheme_wrong_contract("find-system-path", 
                          "(or/c 'home-dir 'pref-dir 'pref-file 'temp-dir\n"
                          "      'init-dir 'init-file 'addon-dir\n"
                          "      'doc-dir 'desk-dir 'sys-dir 'exec-file 'run-file\n"
                          "      'collects-dir 'config-dir 'orig-dir\n"
                          "      'host-collects-dir 'host-config-dir)",
                          0, argc, argv);
    return NULL;
  }

  scheme_security_check_file("find-system-path", NULL, SCHEME_GUARD_FILE_EXISTS);

  {
    Scheme_Object *p;
    char *s;

    s = rktio_system_path(scheme_rktio, which);

    p = scheme_make_sized_offset_path(s, 0, -1, 1);
    
    if (!scheme_is_complete_path(SCHEME_PATH_VAL(p), SCHEME_PATH_LEN(p), SCHEME_PLATFORM_PATH_KIND)) {
      p = scheme_path_to_complete_path(p, original_pwd);
    }
    if (should_be_dir)
      p = scheme_path_to_directory_path(p);
 
    return p;
  }
}

/* should only called from main */
Scheme_Object *scheme_set_exec_cmd(char *s)
{
  if (!exec_cmd) {
    REGISTER_SO(exec_cmd);
    exec_cmd = scheme_make_path(s);
  }

  return exec_cmd;
}

/* should only called from main */
Scheme_Object *scheme_set_run_cmd(char *s)
{
  if (!run_cmd) {
    REGISTER_SO(run_cmd);
    run_cmd = scheme_make_path(s);
  }

  return run_cmd;
}

char *scheme_get_exec_path(void)
{
  if (exec_cmd)
    return SCHEME_PATH_VAL(exec_cmd);
  else
    return NULL;
}

/* should only called from main */
void scheme_set_collects_path(Scheme_Object *p)
{
  if (!collects_path) {
    REGISTER_SO(collects_path);
  }
  collects_path = p;
}

/* should only called from main */
void scheme_set_config_path(Scheme_Object *p)
{
  if (!config_path) {
    REGISTER_SO(config_path);
  }
  config_path = p;
}

/* should only called from main */
void scheme_set_host_collects_path(Scheme_Object *p)
{
  if (!host_collects_path) {
    REGISTER_SO(host_collects_path);
  }
  host_collects_path = p;
}

/* should only called from main */
void scheme_set_host_config_path(Scheme_Object *p)
{
  if (!host_config_path) {
    REGISTER_SO(host_config_path);
  }
  host_config_path = p;
}


void scheme_set_original_dir(Scheme_Object *d)
{
  original_pwd = d;
}

/* should only called from main */
void scheme_set_addon_dir(Scheme_Object *p)
{
  if (!addon_dir) {
    REGISTER_SO(addon_dir);
  }
  addon_dir = p;
}

/********************************************************************************/

#ifdef DOS_FILE_SYSTEM

void scheme_set_dll_path(wchar_t *p)
{
  rktio_set_dll_path(p);
}

wchar_t *scheme_get_dll_path(wchar_t *p)
{
  wchar_t *r, *r2;
  intptr_t len;
  r = rktio_get_dll_path(p);
  if (!r)
    return p;
  len = wcslen(r) + 1;
  r2 = scheme_malloc_atomic(sizeof(wchar_t) * len);
  memcpy(r2, r, sizeof(wchar_t) * len);
  free(r);
  return r2;
}

#endif
