url.hpp File Reference

#include "lolly/data/lolly_tree.hpp"
#include "string.hpp"

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Classes
struct	url_rep
class	url
class	file_url
class	ftp_url
class	blank_url
class	http_url
class	https_url

Macros
#define	URL_SYSTEM   0
#define	URL_UNIX   1
#define	URL_STANDARD   2
#define	URL_CLEAN_UNIX   3
#define	URL_TUPLE   245

Typedefs
typedef lolly_tree< int >	url_tree

Functions
	CONCRETE_CODE (url)
url	as_url (url_tree t)
bool	is_root (url u, string s)
bool	is_root_web (url u)
bool	is_root_blank (url u)
bool	is_rooted (url u, string protocol)
bool	is_rooted_web (url u)
bool	is_rooted_blank (url u)
url	url_none ()
url	url_here ()
url	url_parent ()
url	url_ancestor ()
url	url_root (string protocol)
url	operator* (url u1, url u2)
url	operator* (url u1, const char *name)
url	operator* (url u1, string name)
url	url_concat (url u1, url u2)
url	url_parent (url u)
url	operator| (url u1, url u2)
url	url_or (url u1, url u2)
url	url_wildcard ()
url	url_wildcard (string name)
bool	is_here (url u)
bool	is_parent (url u)
bool	is_ancestor (url u)
bool	is_none (url u)
bool	is_root (url u)
bool	is_concat (url u)
bool	is_or (url u)
bool	is_wildcard (url u)
url	url_path (string s, int type=URL_SYSTEM)
url	url_general (string name, int type)
url	url_unix (string name)
url	url_unix (string dir, string name)
url	url_system (string name)
url	url_system (string dir, string name)
url	url_standard (string name)
url	url_standard (string dir, string name)
url	url_pwd ()
url	url_ramdisc (string contents)
url	head (url u)
url	tail (url u)
string	suffix (url u)
string	suffix (url u, bool use_locase)
string	basename (url u, string suf)
string	basename (url u)
url	glue (url u, string s)
url	unglue (url u, int nr)
url	unblank (url u)
url	relative (url base, url u)
url	delta (url base, url u)
string	get_root (url u)
url	unroot (url u)
url	reroot (url u, string s)
url	expand (url u)
url	sort (url u)
url	factor (url u)
bool	descends (url u, url base)
bool	is_atomic (url u)
bool	is_wildcard (url u, int n)
bool	is_pseudo_atomic (url u)
bool	is_rooted (url u)
bool	is_name (url u)
bool	is_rooted_name (url u)
bool	is_ramdisc (url u)
void	skip_ipv6 (string s, int &i)
string	as_string (url u, int type=URL_SYSTEM)
tm_ostream &	operator<< (tm_ostream &out, url u)
string	as_system_string (url u)
string	as_unix_string (url u)
string	as_standard_string (url u)
url	url_get_name (string s, int type=URL_STANDARD, int i=0)

Macro Definition Documentation

URL_SYSTEM

#define URL_SYSTEM   0

Definition at line 15 of file url.hpp.

URL_UNIX

#define URL_UNIX   1

Definition at line 16 of file url.hpp.

URL_STANDARD

#define URL_STANDARD   2

Definition at line 17 of file url.hpp.

URL_CLEAN_UNIX

#define URL_CLEAN_UNIX   3

Definition at line 18 of file url.hpp.

URL_TUPLE

#define URL_TUPLE   245

Definition at line 20 of file url.hpp.

Typedef Documentation

url_tree

typedef lolly_tree<int> url_tree

Definition at line 26 of file url.hpp.

Function Documentation

CONCRETE_CODE()

CONCRETE_CODE

(

url

)

as_url()

url as_url ( url_tree t )

inline

Definition at line 61 of file url.hpp.

                    {
  return url (t);
}

is_root() [1/2]

bool is_root	(	url	u,
		string	s )

Definition at line 668 of file url.cpp.

                          {
  return is_root (u) && (u[1]->t->label == s);
}

is_root_web()

bool is_root_web

(

url

u

)

Definition at line 672 of file url.cpp.

                    {
  return is_root (u, "http") || is_root (u, "https") || is_root (u, "ftp") ||
         is_root (u, "blank");
}

is_root_blank()

bool is_root_blank

(

url

u

)

Definition at line 22 of file blank_url.cpp.

                      {
  return is_root (u, "blank");
}

is_rooted() [1/2]

bool is_rooted	(	url	u,
		string	protocol )

Definition at line 692 of file url.cpp.

                                   {
  return is_root (u, protocol) ||
         (is_concat (u) && is_rooted (u[1], protocol)) ||
         (is_or (u) && is_rooted (u[1], protocol) &&
          is_rooted (u[2], protocol));
}

is_rooted_web()

bool is_rooted_web

(

url

u

)

Definition at line 700 of file url.cpp.

                      {
  return is_root_web (u) || (is_concat (u) && is_rooted_web (u[1])) ||
         (is_or (u) && is_rooted_web (u[1]) && is_rooted_web (u[2]));
}

is_rooted_blank()

bool is_rooted_blank

(

url

u

)

Definition at line 27 of file blank_url.cpp.

                        {
  return is_root_blank (u) || (is_concat (u) && is_rooted_blank (u[1])) ||
         (is_or (u) && is_rooted_blank (u[1]) && is_rooted_blank (u[2]));
}

url_none()

url url_none

(

)

Definition at line 91 of file url.cpp.

            {
  return as_url (url_tuple ("none"));
}

url_here()

url url_here ( )

inline

Definition at line 122 of file url.hpp.

            {
  return as_url (url_tree ("."));
}

url_parent() [1/2]

url url_parent ( )

inline

Definition at line 127 of file url.hpp.

              {
  return as_url (url_tree (".."));
}

url_ancestor()

url url_ancestor ( )

inline

Definition at line 132 of file url.hpp.

                {
  return as_url (url_tree ("..."));
}

url_root()

url url_root

(

string

protocol

)

Definition at line 96 of file url.cpp.

                           {
  return as_url (url_tuple ("root", protocol));
}

operator*() [1/3]

url operator*	(	url	u1,
		url	u2 )

Definition at line 596 of file url.cpp.

                           {
  if (is_root (u2) || (is_concat (u2) && is_root (u2[1]))) {
    if (is_concat (u1) && is_root_web (u1[1])) {
      if (is_root (u2, "default") ||
          (is_concat (u2) && is_root (u2[1], "default"))) {
        url v= u1[2];
        while (is_concat (v))
          v= v[1];
        if (is_root (u2)) return u1[1] * v;
        return u1[1] * v * u2[2];
      }
      if (is_root (u2, "blank") || (is_concat (u2) && is_root (u2[1], "blank")))
        return reroot (u2, u1[1][1]->t->label);
    }
    if (is_root (u1) && is_rooted (u1, "file")) {
      return u1 * u2[2];
    }
    return u2;
  }
  if (is_here (u1) || (u1->t == "")) return u2;
  if (is_here (u2)) return u1;
  if (is_none (u1)) return url_none ();
  if (is_none (u2)) return url_none ();
  if (u2 == url_parent ()) {
    if (is_root (u1)) return u1;
    if (is_pseudo_atomic (u1) && (!is_parent (u1))) return url_here ();
    if (is_semi_root (u1)) return u1;
  }
  if (is_concat (u2) && (u2[1] == url_parent ())) {
    if (is_root (u1)) return u1 * u2[2];
    if (is_pseudo_atomic (u1) && (!is_parent (u1))) return u2[2];
    if (is_semi_root (u1)) return u1 * u2[2];
  }
  if (is_concat (u1)) return u1[1] * (u1[2] * u2);
  return as_url (url_tuple ("concat", u1->t, u2->t));
}

operator*() [2/3]

url operator*	(	url	u1,
		const char *	name )

Definition at line 634 of file url.cpp.

                                     {
  return u1 * url (name);
}

operator*() [3/3]

url operator*	(	url	u1,
		string	name )

Definition at line 639 of file url.cpp.

                                {
  return u1 * url (name);
}

url_concat()

url url_concat	(	url	u1,
		url	u2 )

Definition at line 644 of file url.cpp.

                            {
  return u1 * u2;
}

url_parent() [2/2]

url url_parent ( url u )

inline

Definition at line 143 of file url.hpp.

                   {
  return u * url_parent ();
}

operator|()

url operator|	(	url	u1,
		url	u2 )

Definition at line 649 of file url.cpp.

                           {
  if (is_none (u1)) return u2;
  if (is_none (u2)) return u1;
  if (is_or (u1)) return u1[1] | (u1[2] | u2);
  if (u1 == u2) return u2;
  if (is_or (u2) && (u1 == u2[1])) return u2;
  return as_url (url_tuple ("or", u1->t, u2->t));
}

url_or()

url url_or	(	url	u1,
		url	u2 )

Definition at line 659 of file url.cpp.

                        {
  return u1 | u2;
}

url_wildcard() [1/2]

url url_wildcard

(

)

Definition at line 101 of file url.cpp.

                { // any url
  return as_url (url_tuple ("wildcard"));
}

url_wildcard() [2/2]

url url_wildcard

(

string

name

)

Definition at line 106 of file url.cpp.

                           { // string with * wildcards
  return as_url (url_tuple ("wildcard", name));
}

is_here()

bool is_here ( url u )

inline

Definition at line 154 of file url.hpp.

                {
  return u->t == ".";
};

is_parent()

bool is_parent ( url u )

inline

Definition at line 158 of file url.hpp.

                  {
  return u->t == "..";
};

is_ancestor()

bool is_ancestor ( url u )

inline

Definition at line 162 of file url.hpp.

                    {
  return u->t == "...";
};

is_none()

bool is_none ( url u )

inline

Definition at line 166 of file url.hpp.

                {
  return u.label () == "none";
};

is_root() [2/2]

bool is_root ( url u )

inline

Definition at line 170 of file url.hpp.

                {
  return u.label () == "root";
};

is_concat()

bool is_concat ( url u )

inline

Definition at line 174 of file url.hpp.

                  {
  return u.label () == "concat";
};

is_or()

bool is_or ( url u )

inline

Definition at line 178 of file url.hpp.

              {
  return u.label () == "or";
};

is_wildcard() [1/2]

bool is_wildcard ( url u )

inline

Definition at line 182 of file url.hpp.

                    {
  return u.label () == "wildcard";
};

url_path()

url url_path	(	string	s,
		int	type = URL_SYSTEM )

Definition at line 247 of file url.cpp.

                              {
  url u= url_get_path (s, type);
  return u;
}

url_general()

url url_general	(	string	name,
		int	type )

Definition at line 273 of file url.cpp.

                                                {
  if (contains (name, "://")) {
    array<string> tokens  = tokenize (name, "://");
    string        protocol= tokens[0];
    string        path    = tokens[1];
    if (N (tokens) == 2 && is_alphanum (protocol) && N (protocol) >= 2) {
      if (protocol == "file") return file_url (path);
      if (protocol == "http") return http_url (path);
      if (protocol == "https") return https_url (path);
      if (protocol == "ftp") return ftp_url (path);
      return url_root (tokens[0]) * url_get_name (tokens[1], type);
    }
  }
  if (starts (name, "local:")) {
    return file_url (name (6, N (name)));
  }
  if (starts (name, "//")) {
    return blank_url (name (2, N (name)));
  }
  if (heuristic_is_path (name, type)) {
    return url_path (name, type);
  }
  if (heuristic_is_default (name, type)) return url_default (name, type);
  if (os_mingw () && heuristic_is_mingw_default (name, type))
    return url_mingw_default (name, type);
  if (type != URL_CLEAN_UNIX) {
    if (heuristic_is_http (name)) return http_url (name);
    if (heuristic_is_ftp (name)) return ftp_url (name);
  }
  return url_get_name (name, type);
}

url_unix() [1/2]

url url_unix

(

string

name

)

Definition at line 31 of file file_url.cpp.

                       {
  return url_general (name, URL_UNIX);
}

url_unix() [2/2]

url url_unix	(	string	dir,
		string	name )

Definition at line 36 of file file_url.cpp.

                                   {
  return url_unix (dir) * url_unix (name);
}

url_system() [1/2]

url url_system

(

string

name

)

Definition at line 306 of file url.cpp.

                         {
  return url_general (name, URL_SYSTEM);
}

url_system() [2/2]

url url_system	(	string	dir,
		string	name )

Definition at line 311 of file url.cpp.

                                     {
  return url_system (dir) * url_system (name);
}

url_standard() [1/2]

url url_standard

(

string

name

)

Definition at line 316 of file url.cpp.

                           {
  return url_general (name, URL_STANDARD);
}

url_standard() [2/2]

url url_standard	(	string	dir,
		string	name )

Definition at line 321 of file url.cpp.

                                       {
  return url_standard (dir) * url_standard (name);
}

url_pwd()

url url_pwd

(

)

Definition at line 326 of file url.cpp.

           {
  char path[TB_PATH_MAXN];
  if (tb_directory_current (path, TB_PATH_MAXN)) {
    return url_system (path);
  }
  else {
    TM_FAILED ("FAILED to get pwd");
    return url_none ();
  }
}

url_ramdisc()

url url_ramdisc

(

string

contents

)

Definition at line 341 of file url.cpp.

                              {
  return as_url (url_tuple ("root", "ramdisc", contents));
}

head()

url head

(

url

u

)

Definition at line 365 of file url.cpp.

             {
  return u * url_parent ();
}

tail()

url tail

(

url

u

)

Definition at line 370 of file url.cpp.

             {
  if (is_concat (u)) {
    if (is_root_web (u[1]) && is_atomic (u[2])) return url_here ();
    return tail (u[2]);
  }
  if (is_or (u)) return tail (u[1]) | tail (u[2]);
  if (is_root (u)) return url_here ();
  return u;
}

suffix() [1/2]

string suffix

(

url

u

)

Definition at line 401 of file url.cpp.

               {
  return suffix (u, true);
}

suffix() [2/2]

string suffix	(	url	u,
		bool	use_locase )

Definition at line 381 of file url.cpp.

                                {
  u= tail (u);
  if (!is_atomic (u)) return "";
  string s= as_string (u);
  int    i, n= N (s);
  for (i= n - 1; i >= 0; i--)
    if (s[i] == '.') break;
  if ((i > 0) && (i < n - 1)) {
    string r= s (i + 1, n);
    while ((N (r) > 0) && (r[N (r) - 1] == '~' || r[N (r) - 1] == '#'))
      r= r (0, N (r) - 1);
    int found= index_of (r, '?');
    if (found != -1) r= r (0, found);
    if (use_locase) return locase_all (r);
    else return r;
  }
  return "";
}

basename() [1/2]

string basename	(	url	u,
		string	suf )

Definition at line 406 of file url.cpp.

                             {
  string s    = as_string (tail (u));
  int    found= index_of (s, '?');
  if (found != -1) s= s (0, found);
  return remove_suffix (s, suf);
}

basename() [2/2]

string basename

(

url

u

)

Definition at line 414 of file url.cpp.

                 {
  string s= suffix (u, false);
  if (!is_empty (s)) s= "." * s;
  return basename (u, s);
}

glue()

url glue	(	url	u,
		string	s )

Definition at line 421 of file url.cpp.

                       {
  if (is_atomic (u)) return as_url (url_tree (u->t->label * s));
  if (is_concat (u)) return u[1] * glue (u[2], s);
  if (is_or (u)) return glue (u[1], s) | glue (u[2], s);
  if (is_none (u)) return u;
  TM_FAILED ("can't glue string to url");
  return u;
}

unglue()

url unglue	(	url	u,
		int	nr )

Definition at line 431 of file url.cpp.

                       {
  if (is_atomic (u))
    return as_url (url_tree (u->t->label (0, max (N (u->t->label) - nr, 0))));
  if (is_concat (u)) return u[1] * unglue (u[2], nr);
  if (is_or (u)) return unglue (u[1], nr) | unglue (u[2], nr);
  if (is_none (u)) return u;
  TM_FAILED ("can't unglue from url");
  return u;
}

unblank()

url unblank

(

url

u

)

Definition at line 442 of file url.cpp.

                {
  if (is_concat (u) && (u[2]->t == "")) return u[1];
  if (is_concat (u)) return u[1] * unblank (u[2]);
  if (is_or (u)) return unblank (u[1]) | unblank (u[2]);
  return u;
}

relative()

url relative	(	url	base,
		url	u )

Definition at line 450 of file url.cpp.

                           {
  return head (base) * u;
}

delta()

url delta	(	url	base,
		url	u )

Definition at line 469 of file url.cpp.

                        {
  if (is_or (u)) return delta (base, u[1]) | delta (base, u[2]);
  url res= delta_sub (base, u);
  if (is_none (res)) return u;
  return res;
}

get_root()

string get_root

(

url

u

)

Definition at line 477 of file url.cpp.

                 {
  return u.protocol ();
}

unroot()

url unroot

(

url

u

)

Definition at line 482 of file url.cpp.

               {
  if (is_concat (u)) return unroot (u[1]) * u[2];
  if (is_or (u)) return unroot (u[1]) | unroot (u[2]);
  if (is_root (u)) return url_here ();
  return u;
}

reroot()

url reroot	(	url	u,
		string	s )

Definition at line 490 of file url.cpp.

                                {
  if (is_concat (u)) return reroot (u[1], protocol) * u[2];
  if (is_or (u)) return reroot (u[1], protocol) | reroot (u[2], protocol);
  if (is_root (u)) return url_root (protocol);
  return u;
}

expand()

url expand

(

url

u

)

Definition at line 512 of file url.cpp.

               {
  if (is_or (u)) return expand (u[1]) | expand (u[2]);
  if (is_concat (u)) return expand (expand (u[1]), expand (u[2]));
  return u;
}

sort()

url sort

(

url

u

)

Definition at line 543 of file url.cpp.

             {
  if (is_or (u)) return sort_sub (u[1], sort (u[2]));
  else return u;
}

factor()

url factor

(

url

u

)

Definition at line 568 of file url.cpp.

               {
  return factor_sub (factor_sorted (sort (u)));
}

descends()

bool descends	(	url	u,
		url	base )

Definition at line 573 of file url.cpp.

                           {
  if (u == base) return true;
  if (is_concat (u) && is_atomic (base)) return u[1] == base;
  if (is_concat (u) && is_concat (base)) {
    url iter_u= u, iter_base= base;
    while (iter_u[1] == iter_base[1]) {
      iter_u   = iter_u[2];
      iter_base= iter_base[2];
      if (is_concat (iter_u) && is_concat (iter_base)) {
        continue;
      }
      else {
        return descends (iter_u, iter_base);
      }
    }
    return false;
  }
  if (is_or (u)) return descends (u[1], base) && descends (u[2], base);
  if (is_or (base)) return descends (u, base[1]) || descends (u, base[2]);
  return false;
}

is_atomic()

bool is_atomic

(

url

u

)

Definition at line 664 of file url.cpp.

                  {
  return is_atomic (u->t);
}

is_wildcard() [2/2]

bool is_wildcard	(	url	u,
		int	n )

Definition at line 677 of file url.cpp.

                           {
  return is_tuple (u->t, "wildcard", n);
}

is_pseudo_atomic()

bool is_pseudo_atomic

(

url

u

)

Definition at line 681 of file url.cpp.

                         {
  return is_atomic (u->t) || is_tuple (u->t, "wildcard", 1);
}

is_rooted() [2/2]

bool is_rooted

(

url

u

)

Definition at line 686 of file url.cpp.

                  {
  return is_root (u) || (is_concat (u) && is_rooted (u[1])) ||
         (is_or (u) && is_rooted (u[1]) && is_rooted (u[2]));
}

is_name()

bool is_name

(

url

u

)

Definition at line 706 of file url.cpp.

                {
  if (is_atomic (u)) return true;
  if (!is_concat (u)) return false;
  return is_name (u[1]) && is_name (u[2]);
}

is_rooted_name()

bool is_rooted_name

(

url

u

)

Definition at line 713 of file url.cpp.

                       {
  return is_concat (u) && is_root (u[1]) && is_name (u[2]);
}

is_ramdisc()

bool is_ramdisc

(

url

u

)

Definition at line 724 of file url.cpp.

                   {
  return is_concat (u) && is_root (u[1], "ramdisc");
}

skip_ipv6()

void skip_ipv6	(	string	s,
		int &	i )

Definition at line 114 of file url.cpp.

                             {
  i++;
  while (i < N (s) &&
         (s[i] == ':' || (s[i] >= '0' && s[i] <= '9') ||
          (s[i] >= 'a' && s[i] <= 'f') || (s[i] >= 'A' && s[i] <= 'F')))
    i++;
  if (i < N (s) && s[i] == ']') i++;
}

as_string()

string as_string	(	url	u,
		int	type = URL_SYSTEM )

Definition at line 729 of file url.cpp.

                            {
  // This routine pretty prints an url as a string.
  // FIXME: the current algorithm is quadratic in time.
  if (is_none (u)) return "{}";
  if (is_atomic (u)) return u->t->label;
  if (is_concat (u)) {
    int stype= type;
    if (is_root (u[1]) &&
        !(is_root (u[1], "default") || is_root (u[1], "file"))) {
      stype= URL_STANDARD;
    }
    string sep= (stype == URL_SYSTEM ? string (URL_CONCATER) : string ("/"));
    string s1 = as_string (u[1], type);
    string s2 = as_string (u[2], stype);
    if (is_root (u[1], "default")) s1= "";
    if ((!is_name (u[1])) && (!is_root (u[1]))) s1= "{" * s1 * "}";
    if ((!is_concat (u[2])) && (!is_atomic (u[2])) && (!is_wildcard (u[2], 1)))
      s2= "{" * s2 * "}";
    if (os_win () && // have to return the windows format
        ((is_root (u[1], "default") && type == URL_SYSTEM) ||
         is_root (u[1], "file"))) {
      string root, remain;
      if (is_concat (u[2])) {
        root= as_string (u[2][1], type);
        // root might be unit letter or hostname. It depends on the length
        remain= as_string (u[2][2], type);
      }
      else {
        root  = s2;
        remain= "";
      }
      if (is_root (u[1], "default")) {
        if (N (root) == 1) return root * ":" * sep * remain; // drive letter
        else return "\\\\" * root * "\\" * remain;
      }
      else {
        if (N (root) == 1)
          return s1 * "/" * root * ":" * sep * remain; // local file
        else return s1 * root * "/" * remain;          // remote
      }
    }
    return s1 * sep * s2;
  }
  if (is_or (u)) {
    string s1= as_string (u[1], type);
    string s2= as_string (u[2], type);
    if (!is_name_in_path (u[1])) s1= "{" * s1 * "}";
    if ((!is_or (u[2])) && (!is_name_in_path (u[2]))) s2= "{" * s2 * "}";
    if (os_win ()) {
      if (type == URL_STANDARD) return s1 * ":" * s2;
      else return s1 * string (URL_SEPARATOR) * s2;
    }
    else {
      return s1 * string (URL_SEPARATOR) * s2;
    }
  }
  if (os_win ()) {
    if (is_root (u, "default")) {
      int stype= type;
      if (is_root (u[1]) && (!is_root (u[1], "default"))) stype= URL_STANDARD;
      if (stype == URL_SYSTEM) return "";
      else return "/";
    }
  }
  else {
    if (is_root (u, "default")) return "/";
  }
  if (is_root (u, "blank")) return "/";
  if (is_root (u, "file")) return u[1]->t->label * "://";
  if (is_root (u)) return u[1]->t->label * ":/";
  if (is_wildcard (u, 0)) return "**";
  if (is_wildcard (u, 1)) return u->t[1]->label;
  TM_FAILED ("bad url");
  return "";
}

operator<<()

tm_ostream & operator<<	(	tm_ostream &	out,
		url	u )

Definition at line 805 of file url.cpp.

                                    {
  return out << as_string (u, URL_SYSTEM);
}

as_system_string()

string as_system_string ( url u )

inline

Definition at line 245 of file url.hpp.

                         {
  return as_string (u, URL_SYSTEM);
}

as_unix_string()

string as_unix_string ( url u )

inline

Definition at line 249 of file url.hpp.

                       {
  return as_string (u, URL_UNIX);
}

as_standard_string()

string as_standard_string ( url u )

inline

Definition at line 253 of file url.hpp.

                           {
  return as_string (u, URL_STANDARD);
}

url_get_name()

url url_get_name	(	string	s,
		int	type = URL_STANDARD,
		int	i = 0 )

Definition at line 190 of file url.cpp.

                                         {
  char      sep   = (type == URL_SYSTEM) ? URL_CONCATER : '/';
  int       n     = N (s);
  list<url> u_list= list<url> ();
  while (i < n) {
    int start= i;
    while ((i < n) && (s[i] != sep) && (s[i] != '/')) {
      if (s[i] == '[') skip_ipv6 (s, i);
      else i++;
    }
    if (i > start) {
      url u = url_get_atom (s (start, i), type);
      u_list= list (u, u_list);
    }
    else if (i == start) {
      i++;
      if (i == n) {
        u_list= list (as_url (url_tree ("")), u_list);
      }
    }
  }
 
  if (is_nil (u_list)) return as_url (url_tree (""));
  url ret= u_list->item;
  u_list = u_list->next;
  while (!is_nil (u_list)) {
    url u= u_list->item;
    if (is_here (u) || (u->t == "")) {
      // do nothing
    }
    else if (is_atomic (u)) {
      ret= as_url (url_tuple ("concat", u->t, ret->t));
    }
    else {
      ret= u * ret;
    }
    u_list= u_list->next;
  }
  return ret;
}