anchor.diff:  %%      partition("foo/bar", "/") = {"foo", "/", "bar"},
   %%      partition("foo", "/") = {"foo", "", ""}.
   partition(String, Sep) ->
  -    case partition(String, Sep, []) of
  -        undefined ->
  -            {String, "", ""};
  -        Result ->
  -            Result
  -    end.
  +  case partition(String, Sep, []) of
  +    undefined ->
  +      {String, "", ""};
  +    Result ->
  +      Result
  +  end.
   
   partition("", _Sep, _Acc) ->
  -    undefined;
  +  undefined;
   partition(S, Sep, Acc) ->
  -    case partition2(S, Sep) of
  -        undefined ->
  -            [C | Rest] = S,
  -            partition(Rest, Sep, [C | Acc]);
  -        Rest ->
  -            {lists:reverse(Acc), Sep, Rest}
  -    end.
  +  case partition2(S, Sep) of
  +    undefined ->
  +      [C | Rest] = S,
  +      partition(Rest, Sep, [C | Acc]);
  +    Rest ->
  +      {lists:reverse(Acc), Sep, Rest}
  +  end.
   
   partition2(Rest, "") ->
  -    Rest;
  +  Rest;
   partition2([C | R1], [C | R2]) ->
  -    partition2(R1, R2);
  +  partition2(R1, R2);
   partition2(_S, _Sep) ->
  -    undefined.
  +  undefined.
   
   
   
  
positive.code: %%      path_split("foo/bar") = {"foo", "bar"},
  %%      path_split("/foo/bar") = {"", "foo/bar"}.
  path_split(S) ->
      path_split(S, []).
  
  path_split("", Acc) ->
      {lists:reverse(Acc), ""};
  path_split("/" ++ Rest, Acc) ->
      {lists:reverse(Acc), Rest};
  path_split([C | Rest], Acc) ->
      path_split(Rest, [C | Acc]).
  
  
  %% @spec urlunsplit({Scheme, Netloc, Path, Query, Fragment}) -> string()
  %% @doc Assemble a URL from the 5-tuple. Path must be absolute.
  urlunsplit({Scheme, Netloc, Path, Query, Fragment}) ->
      lists:flatten([case Scheme of "" -> "";  _ -> [Scheme, "://"] end,
                     Netloc,
                     urlunsplit_path({Path, Query, Fragment})]).
  
  %% @spec urlunsplit_path({Path, Query, Fragment}) -> string()
  %% @doc Assemble a URL path from the 3-tuple.
  urlunsplit_path({Path, Query, Fragment}) ->
      lists:flatten([Path,
                     case Query of "" -> ""; _ -> [$? | Query] end,
                     case Fragment of "" -> ""; _ -> [$# | Fragment] end]).
  
  %% @spec urlsplit_path(Url) -> {Path, Query, Fragment}
  %% @doc Return a 3-tuple, does not expand % escapes. Only supports HTTP style
  %%      paths.
  urlsplit_path(Path) ->
      urlsplit_path(Path, []).
  
  urlsplit_path("", Acc) ->
      {lists:reverse(Acc), "", ""};
  urlsplit_path("?" ++ Rest, Acc) ->
      {Query, Fragment} = urlsplit_query(Rest),
      {lists:reverse(Acc), Query, Fragment};
  urlsplit_path("#" ++ Rest, Acc) ->
      {lists:reverse(Acc), "", Rest};
  urlsplit_path([C | Rest], Acc) ->
      urlsplit_path(Rest, [C | Acc]).
  
  urlsplit_query(Query) ->
      urlsplit_query(Query, []).
  
  urlsplit_query("", Acc) ->
      {lists:reverse(Acc), ""};
  urlsplit_query("#" ++ Rest, Acc) ->
      {lists:reverse(Acc), Rest};
  urlsplit_query([C | Rest], Acc) ->
      urlsplit_query(Rest, [C | Acc]).
  
  %% @spec guess_mime(string()) -> string()
  %% @doc  Guess the mime type of a file by the extension of its filename.
  guess_mime(File) ->
      case filename:extension(File) of
          ".html" ->
              "text/html";
          ".xhtml" ->
              "application/xhtml+xml";
          ".xml" ->
              "application/xml";
          ".css" ->
              "text/css";
          ".js" ->
              "application/x-javascript";
          ".jpg" ->
              "image/jpeg";
          ".gif" ->
              "image/gif";
          ".png" ->
              "image/png";
          ".swf" ->
              "application/x-shockwave-flash";
          ".zip" ->
              "application/zip";
          ".bz2" ->
              "application/x-bzip2";
          ".gz" ->
              "application/x-gzip";
          ".tar" ->
              "application/x-tar";
          ".tgz" ->
              "application/x-gzip";
          ".txt" ->
              "text/plain";
          ".doc" ->
              "application/msword";
          ".pdf" ->
              "application/pdf";
          ".xls" ->
              "application/vnd.ms-excel";
          ".rtf" ->
              "application/rtf";
          ".mov" ->
              "video/quicktime";
          ".mp3" ->
              "audio/mpeg";
          ".z" ->
              "application/x-compress";
          ".wav" ->
              "audio/x-wav";
          ".ico" ->
              "image/x-icon";
          ".bmp" ->
              "image/bmp";
          ".m4a" ->
              "audio/mpeg";
          ".m3u" ->
              "audio/x-mpegurl";
          ".exe" ->
              "application/octet-stream";
          ".csv" ->
              "text/csv";
          _ ->
              "text/plain"
      end.
  
  %% @spec parse_header(string()) -> {Type, [{K, V}]}
  %% @doc  Parse a Content-Type like header, return the main Content-Type
  %%       and a property list of options.
  parse_header(String) ->
      %% TODO: This is exactly as broken as Python's cgi module.
      %%       Should parse properly like mochiweb_cookies.
      [Type | Parts] = [string:strip(S) || S <- string:tokens(String, ";")],
      F = fun (S, Acc) ->
                  case lists:splitwith(fun (C) -> C =/= $= end, S) of
                      {"", _} ->
                          %% Skip anything with no name
                          Acc;
                      {_, ""} ->
                          %% Skip anything with no value
                          Acc;
                      {Name, [$\= | Value]} ->
                          [{string:to_lower(string:strip(Name)),
                            unquote_header(string:strip(Value))} | Acc]
                  end
          end,
      {string:to_lower(Type),
       lists:foldr(F, [], Parts)}.
  
  unquote_header("\"" ++ Rest) ->
      unquote_header(Rest, []);
  unquote_header(S) ->
      S.
  
  unquote_header("", Acc) ->
      lists:reverse(Acc);
  unquote_header("\"", Acc) ->
      lists:reverse(Acc);
  unquote_header([$\\, C | Rest], Acc) ->
      unquote_header(Rest, [C | Acc]);
  unquote_header([C | Rest], Acc) ->
      unquote_header(Rest, [C | Acc]).
  
  %% @spec record_to_proplist(Record, Fields) -> proplist()
  %% @doc calls record_to_proplist/3 with a default TypeKey of '__record'
  record_to_proplist(Record, Fields) ->
      record_to_proplist(Record, Fields, '__record').
  
  %% @spec record_to_proplist(Record, Fields, TypeKey) -> proplist()
  %% @doc Return a proplist of the given Record with each field in the
  
negative.code: %%      is not safe. safe relative paths can be joined with an absolute path
  %%      and will result in a subdirectory of the absolute path.
  safe_relative_path("/" ++ _) ->
    undefined;
  safe_relative_path(P) ->
    safe_relative_path(P, []).
  
  safe_relative_path("", Acc) ->
    case Acc of
      [] ->
        "";
      _ ->
        string:join(lists:reverse(Acc), "/")
    end;
  safe_relative_path(P, Acc) ->
    case partition(P, "/") of
      {"", "/", _} ->
  %% /foo or foo//bar
        undefined;
      {"..", _, _} when Acc =:= [] ->
        undefined;
      {"..", _, Rest} ->
        safe_relative_path(Rest, tl(Acc));
      {Part, "/", ""} ->
        safe_relative_path("", ["", Part | Acc]);
      {Part, _, Rest} ->
        safe_relative_path(Rest, [Part | Acc])
    end.
  
  %% @spec shell_quote(string()) -> string()
  %% @doc Quote a string according to UNIX shell quoting rules, returns a string
  %%      surrounded by double quotes.
  shell_quote(L) ->
    shell_quote(L, [$\"]).
  
  %% @spec cmd_port([string()], Options) -> port()
  %% @doc open_port({spawn, mochiweb_util:cmd_string(Argv)}, Options).
  cmd_port(Argv, Options) ->
                       open_port({spawn, cmd_string(Argv)}, Options).
  
  %% @spec cmd([string()]) -> string()
  %% @doc os:cmd(cmd_string(Argv)).
  cmd(Argv) ->
    os:cmd(cmd_string(Argv)).
  
  %% @spec cmd_string([string()]) -> string()
  %% @doc Create a shell quoted command string from a list of arguments.
  cmd_string(Argv) ->
    join([shell_quote(X) || X <- Argv], " ").
  
  %% @spec join([string()], Separator) -> string()
  %% @doc Join a list of strings together with the given separator
  %%      string or char.
  join([], _Separator) ->
    [];
  join([S], _Separator) ->
    lists:flatten(S);
  join(Strings, Separator) ->
    lists:flatten(revjoin(lists:reverse(Strings), Separator, [])).
  
  revjoin([], _Separator, Acc) ->
    Acc;
  revjoin([S | Rest], Separator, []) ->
    revjoin(Rest, Separator, [S]);
  revjoin([S | Rest], Separator, Acc) ->
    revjoin(Rest, Separator, [S, Separator | Acc]).
  
  %% @spec quote_plus(atom() | integer() | float() | string() | binary()) -> string()
  %% @doc URL safe encoding of the given term.
  quote_plus(Atom) when is_atom(Atom) ->
    quote_plus(atom_to_list(Atom));
  quote_plus(Int) when is_integer(Int) ->
    quote_plus(integer_to_list(Int));
  quote_plus(Binary) when is_binary(Binary) ->
    quote_plus(binary_to_list(Binary));
  quote_plus(Float) when is_float(Float) ->
    quote_plus(mochinum:digits(Float));
  quote_plus(String) ->
    quote_plus(String, []).
  
  quote_plus([], Acc) ->
    lists:reverse(Acc);
  quote_plus([C | Rest], Acc) when ?QS_SAFE(C) ->
    quote_plus(Rest, [C | Acc]);
  quote_plus([$\s | Rest], Acc) ->
    quote_plus(Rest, [$+ | Acc]);
  quote_plus([C | Rest], Acc) ->
    <<Hi:4, Lo:4>> = <<C>>,
    quote_plus(Rest, [hexdigit(Lo), hexdigit(Hi), ?PERCENT | Acc]).
  
  %% @spec urlencode([{Key, Value}]) -> string()
  %% @doc URL encode the property list.
  urlencode(Props) ->
    RevPairs = lists:foldl(fun ({K, V}, Acc) ->
                               [[quote_plus(K), $=, quote_plus(V)] | Acc]
                           end, [], Props),
    lists:flatten(revjoin(RevPairs, $&, [])).
  
  %% @spec parse_qs(string() | binary()) -> [{Key, Value}]
  %% @doc Parse a query string or application/x-www-form-urlencoded.
  -spec(parse_qs/1 :: (list()) -> [tuple()]).
  parse_qs(Binary) when is_binary(Binary) ->
    parse_qs(binary_to_list(Binary));
  parse_qs([$? | Rest]) ->
    parse_qs(Rest);
  parse_qs(String) ->
    parse_qs(String, []).
  
  parse_qs([], Acc) ->
    lists:reverse(Acc);
  parse_qs(String, Acc) ->
    case parse_qs_key(String) of
      {[], Key, Rest} ->
        {Value, Rest1} = parse_qs_value(Rest),
        parse_qs(Rest1, [{Key, Value} | Acc]);
      {Parents, Key, Rest} ->
        {Value, Rest1} = parse_qs_value(Rest),
        Acc1 = parse_qs_merge(Parents, Key, Value, Acc),
        parse_qs(Rest1, Acc1)
    end.
  
  parse_qs_key(String) ->
    parse_qs_key(String, [], []).
  
  parse_qs_key([], Parents, Acc) ->
    {Parents, qs_revdecode(Acc), ""};
  parse_qs_key([$= | Rest], Parents, Acc) ->
    {Parents, qs_revdecode(Acc), Rest};
  parse_qs_key(Rest=[$; | _], Parents, Acc) ->
    {Parents, qs_revdecode(Acc), Rest};
  parse_qs_key(Rest=[$& | _], Parents, Acc) ->
    {Parents, qs_revdecode(Acc), Rest};
  parse_qs_key([?LBRACE | Rest], Parents, Acc) ->
    case parse_qs_parent(Rest) of
      {valid, Key, Rest1} ->
        parse_qs_key(Rest1, [qs_revdecode(Acc) | Parents], Key);
      {invalid, KeyRest, Rest1} ->
        {Parents, qs_revdecode([KeyRest | Acc]), Rest1}
    end;
  parse_qs_key([C | Rest], Parents, Acc) ->
    parse_qs_key(Rest, Parents, [C | Acc]).
  
  
  parse_qs_parent(String) ->
    parse_qs_parent(String, []).
  parse_qs_parent([], Acc) ->
    {invalid, Acc, ""};
  parse_qs_parent([$= | Rest], Acc) ->
    {invalid, Acc, Rest};
  parse_qs_parent(Rest=[$; | _], Acc) ->
    {invalid, Acc, Rest};
  parse_qs_parent(Rest=[$& | _], Acc) ->
    {invalid, Acc, Rest};
  parse_qs_parent([?RBRACE | Rest], Acc) ->
    {valid, Acc, Rest};
  parse_qs_parent([C | Rest], Acc) ->
    parse_qs_parent(Rest, [C | Acc]).
  
  
  parse_qs_value(String) ->
    parse_qs_value(String, []).
  
  parse_qs_value([], Acc) ->
    {qs_revdecode(Acc), ""};
  parse_qs_value([$; | Rest], Acc) ->
    {qs_revdecode(Acc), Rest};
  parse_qs_value([$& | Rest], Acc) ->
    {qs_revdecode(Acc), Rest};
  parse_qs_value([C | Rest], Acc) ->
    parse_qs_value(Rest, [C | Acc]).
  
  
  parse_qs_merge([], Key, Value, Acc) ->
    lists:ukeysort(1, [{Key, Value}] ++ Acc);
  parse_qs_merge([H|T], Key, Value, Acc) ->
    case proplists:get_value(H, Acc) of
      undefined ->
        [{H, parse_qs_merge(T, Key, Value, []) ++ Acc}];
      PropList ->
        Merger = parse_qs_merge(T, Key, Value, PropList),
        lists:ukeysort(1, [{H, Merger}] ++ Acc)
    end.
  
  
  %% @spec unquote(string() | binary()) -> string()
  %% @doc Unquote a URL encoded string.
  unquote(Binary) when is_binary(Binary) ->
    unquote(binary_to_list(Binary));
  unquote(String) ->
    qs_revdecode(lists:reverse(String)).
  
  qs_revdecode(S) ->
    qs_revdecode(S, []).
  
  qs_revdecode([], Acc) ->
    Acc;
  qs_revdecode([$+ | Rest], Acc) ->
    qs_revdecode(Rest, [$\s | Acc]);
  qs_revdecode([Lo, Hi, ?PERCENT | Rest], Acc) when ?IS_HEX(Lo), ?IS_HEX(Hi) ->
    qs_revdecode(Rest, [(unhexdigit(Lo) bor (unhexdigit(Hi) bsl 4)) | Acc]);
  qs_revdecode([C | Rest], Acc) ->
    qs_revdecode(Rest, [C | Acc]).
  
  %% @spec urlsplit(Url) -> {Scheme, Netloc, Path, Query, Fragment}
  %% @doc Return a 5-tuple, does not expand % escapes. Only supports HTTP style
  %%      URLs.
  urlsplit(Url) ->
    {Scheme, Url1} = urlsplit_scheme(Url),
    {Netloc, Url2} = urlsplit_netloc(Url1),
    {Path, Query, Fragment} = urlsplit_path(Url2),
    {Scheme, Netloc, Path, Query, Fragment}.
  
  urlsplit_scheme(Url) ->
    urlsplit_scheme(Url, []).
  
  urlsplit_scheme([], Acc) ->
    {"", lists:reverse(Acc)};
  urlsplit_scheme(":" ++ Rest, Acc) ->
    {string:to_lower(lists:reverse(Acc)), Rest};
  urlsplit_scheme([C | Rest], Acc) ->
    urlsplit_scheme(Rest, [C | Acc]).
  
  urlsplit_netloc("//" ++ Rest) ->
    urlsplit_netloc(Rest, []);
  urlsplit_netloc(Path) ->
    {"", Path}.
  
  urlsplit_netloc(Rest=[C | _], Acc) when C =:= $/; C =:= $?; C =:= $# ->
    {lists:reverse(Acc), Rest};
  urlsplit_netloc([C | Rest], Acc) ->
    urlsplit_netloc(Rest, [C | Acc]).
  
  
  %% @spec path_split(string()) -> {Part, Rest}
  