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//! RXML parser and compiler framework. 
//! 
//! Created 1999-07-30 by Martin Stjernholm. 
//! 
//! $Id: module.pmod,v 1.19 2000/01/15 19:35:07 mast Exp $ 
 
//! Kludge: Must use "RXML.refs" somewhere for the whole module to be 
//! loaded correctly. 
 
//! WARNING: This API is not yet set in stone; expect incompatible 
//! changes. 
 
#pragma strict_types 
 
 
class Tag 
//! Interface class for the static information about a tag. 
{ 
  constant is_RXML_Tag = 1; 
 
  //! Interface. 
 
  //!string name; 
  //! The name of the tag. Required and considered constant. 
 
  int flags; 
  //! Various bit flags that affect parsing; see the FLAG_* constants. 
  //! RXML.Frame.flags is initialized from this. 
 
  mapping(string:Type) req_arg_types; 
  mapping(string:Type) opt_arg_types; 
  //! Define to declare the names and types of the required and 
  //! optional arguments. If a type specifies a parser, it'll be used 
  //! on the argument value. Note that the order in which arguments 
  //! are parsed is arbitrary. 
 
  Type content_type = t_text (PHtml); 
  //! The handled type of the content, if the tag is used as a 
  //! container. It's taken from the actual result type if set to 
  //! zero. 
  //! 
  //! This default says it's text, but the HTML parser is used to read 
  //! it, which means that the content is preparsed with HTML syntax. 
  //! Use t_text directly with no parser to get the raw text. 
 
  array(Type) result_types = ({t_text}); 
  //! The possible types of the result, in order of precedence. If a 
  //! result type has a parser, it'll be used to parse any strings 
  //! gotten from Frame.do_return (see that function for details). 
 
  string scope_name; 
  //! RXML.Frame.scope_name is initialized from this. 
 
  TagSet additional_tags, local_tags; 
  //! RXML.Frame.additional_tags and RXML.Frame.local_tags are 
  //! initialized from these. 
 
  function(:Frame) frame(); 
  //! This function should return an object to be used as a frame. The 
  //! frame object must (in practice) inherit RXML.Frame. 
 
  //! Services. 
 
  inline Frame `() (mapping(string:mixed) args, void|mixed|PCode content) 
  //! Make an initialized frame for the tag. Typically useful when 
  //! returning generated tags from e.g. RXML.Frame.do_return(). The 
  //! argument values and the content are not parsed; see 
  //! RXML.Frame.do_return() for details. Note: Never reuse the same 
  //! frame object. 
  { 
    Tag this = this_object(); 
    Frame frame = ([function(:Frame)] this->frame)(); 
    frame->tag = this; 
    frame->flags = flags; 
    if (scope_name) frame->scope_name = scope_name; 
    if (additional_tags) frame->additional_tags = additional_tags; 
    if (local_tags) frame->local_tags = local_tags; 
    frame->args = args; 
    if (!zero_type (content)) frame->content = content; 
    return frame; 
  } 
 
  // Internals. 
 
  array _handle_tag (TagSetParser parser, mapping(string:string) args, 
                     void|string content) 
  // Callback for tag set parsers. Returns a sequence of result values 
  // to be added to the result queue. Note that this function handles 
  // an unwind frame for the parser. 
  { 
    Context ctx = parser->context; 
    // FIXME: P-code generation. 
    Frame frame; 
    if (mapping(string:mixed)|mapping(object:array) ustate = ctx->unwind_state) 
      if (ustate[parser]) frame = [object(Frame)] ustate[parser][0]; 
      else frame = `() (args, Void); 
    else frame = `() (args, Void); 
 
    mixed err = catch { 
      frame->_eval (parser, args, content); 
      return frame->result == Void ? ({}) : ({frame->result}); 
    }; 
 
    if (objectp (err) && ([object] err)->thrown_at_unwind) { 
      mapping(string:mixed)|mapping(object:array) ustate = ctx->unwind_state; 
      if (!ustate) ustate = ctx->unwind_state = ([]); 
#ifdef DEBUG 
      if (err != frame) 
        error ("Internal error: Unexpected unwind object catched.\n"); 
      if (ustate[parser]) 
        error ("Internal error: Clobbering unwind state for parser.\n"); 
#endif 
      ustate[parser] = ({err}); 
      err = parser; 
    } 
 
    throw (err); 
  } 
 
  string _sprintf() 
  { 
    return "RXML.Tag(" + [string] this_object()->name + ")"; 
  } 
} 
 
 
class TagSet 
//! Contains a set of tags. Tag sets can import other tag sets, and 
//! later changes are propagated. Parser instances (contexts) to parse 
//! data are created from this. TagSet objects may somewhat safely be 
//! destructed explicitly; the tags in a destructed tag set will not 
//! be active in parsers that are instantiated later, but will work in 
//! current instances. 
{ 
  string name; 
  //! Used for identification only. 
 
  string prefix; 
  //! A prefix that may precede the tags. If zero, it's up to the 
  //! importing tag set(s). 
 
  int prefix_required; 
  //! The prefix must precede the tags. 
 
  array(TagSet) imported = ({}); 
  //! Other tag sets that will be used. The precedence is local tags 
  //! first, then imported from left to right. It's not safe to 
  //! destructively change entries in this array. 
 
  function(Context:void) prepare_context; 
  //! If set, this is a function that will be called before a new 
  //! Context object is taken into use. It'll typically prepare 
  //! predefined scopes and variables. The functions will be called in 
  //! order of precedence; highest last. 
 
  int generation = 1; 
  //! A number that is increased every time something changes in this 
  //! object or in some tag set it imports. 
 
#define LOW_TAG_TYPE                                                  \ 
  string|array|                                                         \ 
  function(:int(1..1)|string|array)|                                    \ 
  function(object,mapping(string:string):int(1..1)|string|array) 
 
#define LOW_CONTAINER_TYPE                                            \ 
  string|array|                                                         \ 
  function(:int(1..1)|string|array)|                                    \ 
  function(object,mapping(string:string),string:int(1..1)|string|array) 
 
#define LOW_ENTITY_TYPE                                                       \ 
  string|array|                                                         \ 
  function(:int(1..1)|string|array)|                                    \ 
  function(object:int(1..1)|string|array) 
 
  mapping(string:LOW_TAG_TYPE) low_tags; 
  mapping(string:LOW_CONTAINER_TYPE) low_containers; 
  mapping(string:LOW_ENTITY_TYPE) low_entities; 
  //! Passed directly to Parser.HTML when that parser is used. This is 
  //! intended for compatibility only and might eventually be removed. 
  //! Note: Changes in these aren't tracked; changed() must be called. 
 
  static void create (string _name, void|array(Tag) _tags) 
  //! 
  { 
    name = _name; 
    if (_tags) tags = mkmapping ([array(string)] _tags->name, _tags); 
  } 
 
  void add_tag (Tag tag) 
  //! 
  { 
    tags[tag->name] = tag; 
    changed(); 
  } 
 
  void add_tags (array(Tag) _tags) 
  //! 
  { 
    tags += mkmapping (/*[array(string)]HMM*/ _tags->name, _tags); 
    changed(); 
  } 
 
  void remove_tag (string|Tag tag) 
  //! 
  { 
    if (stringp (tag)) 
      m_delete (tags, tag); 
    else for (string n; !zero_type (n = search (tags, [object(Tag)] tag));) 
      m_delete (tags, n); 
    changed(); 
  } 
 
  local Tag|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE) get_local_tag (string name) 
  //! Returns the tag definition for the given name in this tag set. 
  //! The return value is either a Tag object or an array ({low_tag, 
  //! low_container}), where one element always is zero. 
  { 
    if (Tag tag = tags[name]) return tag; 
    else if (LOW_CONTAINER_TYPE cdef = low_containers && low_containers[name]) 
      return ({0, cdef}); 
    else if (LOW_TAG_TYPE tdef = low_tags && low_tags[name]) 
      return ({tdef, 0}); 
    else return 0; 
  } 
 
  array(Tag) get_local_tags() 
  //! Doesn't return the low tag/container definitions. 
  { 
    return values (tags); 
  } 
 
  Tag|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE) get_tag (string name) 
  //! Returns the active tag definition for the given name. The return 
  //! value is the same as for get_local_tag(). 
  { 
    if (object(Tag)|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE) def = get_local_tag (name)) 
      return def; 
    foreach (imported, TagSet tag_set) 
      if (object(Tag) tag = [object(Tag)] tag_set->get_tag (name)) return tag; 
    return 0; 
  } 
 
  Tag|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE) get_overridden_tag ( 
    Tag|LOW_TAG_TYPE|LOW_CONTAINER_TYPE tagdef, void|string name) 
  //! Returns the tag definition that the given one overrides, or zero 
  //! if none. tag is a Tag object or a low tag/container definition. 
  //! In the latter case, the tag name must be given as the second 
  //! argument. The return value is the same as for get_local_tag(). 
  { 
    if (objectp (tagdef) && ([object] tagdef)->is_RXML_Tag) 
      name = [string] ([object] tagdef)->name; 
#ifdef MODULE_DEBUG 
    if (!name) error ("Need tag name.\n"); 
#endif 
    if (tags[name] == tagdef || 
        (low_containers && low_containers[name] == tagdef) || 
        (low_tags && low_tags[name] == tagdef)) { 
      foreach (imported, TagSet tag_set) 
        if (object(Tag)|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE) tagdef = 
            tag_set->get_tag (name)) return tagdef; 
    } 
    else { 
      int found = 0; 
      foreach (imported, TagSet tag_set) 
        if (object(Tag)|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE) subtag = 
            tag_set->get_tag (name)) 
          if (found) return subtag; 
          else if (arrayp (subtag) ? 
                   subtag[0] == tagdef || subtag[1] == tagdef : 
                   subtag == tagdef) 
            if ((subtag = tag_set->get_overridden_tag (tagdef, name))) 
              return subtag; 
            else found = 1; 
    } 
    return 0; 
  } 
 
  array(Tag|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE)) get_overridden_tags (string name) 
  //! Returns all tag definitions for the given name, i.e. including 
  //! the overridden ones. A tag to the left overrides one to the 
  //! right. The elements in the returned array are the same as for 
  //! get_local_tag(). 
  { 
    if (object(Tag)|array(LOW_TAG_TYPE|LOW_CONTAINER_TYPE) def = get_local_tag (name)) 
      return ({def}) + imported->get_all_tags (name) * ({}); 
    else return imported->get_all_tags (name) * ({}); 
  } 
 
  multiset(string) get_tag_names() 
  //! 
  { 
    multiset(string) res = (multiset) indices (tags); 
    if (low_tags) res |= (multiset) indices (low_tags); 
    if (low_containers) res |= (multiset) indices (low_containers); 
    return `| (res, @imported->get_tag_names()); 
  } 
 
  mixed `->= (string var, mixed val) 
  { 
    switch (var) { 
      case "imported": 
        (imported - ({0}))->dont_notify (changed); 
        imported = [array(TagSet)] val; 
        imported->do_notify (changed); 
        break; 
      default: 
        ::`->= (var, val); 
    } 
    changed(); 
    return val; 
  } 
 
  mixed `[]= (string var, mixed val) {return `->= (var, val);} 
 
  Parser `() (Type top_level_type, void|RequestID id) 
  //! Creates a new context for parsing content of the specified type, 
  //! and returns the parser object for it. id is put into the 
  //! context. 
  { 
    Context ctx = Context (this_object(), id); 
    if (!prepare_funs) prepare_funs = get_prepare_funs(); 
    prepare_funs -= ({0}); 
    prepare_funs (ctx); 
    return ctx->new_parser (top_level_type); 
  } 
 
  void changed() 
  //! Should be called whenever something is changed. Done 
  //! automatically most of the time, however. 
  { 
    generation++; 
    prepare_funs = 0; 
    (notify_funcs -= ({0}))(); 
    set_weak_flag (notify_funcs, 1); 
  } 
 
  // Internals. 
 
  void do_notify (function(:void) func) 
  { 
    notify_funcs |= ({func}); 
    set_weak_flag (notify_funcs, 1); 
  } 
 
  void dont_notify (function(:void) func) 
  { 
    notify_funcs -= ({func}); 
    set_weak_flag (notify_funcs, 1); 
  } 
 
  void destroy() 
  { 
    catch (changed()); 
  } 
 
  private mapping(string:Tag) tags = ([]); 
  // Private since we want to track changes in this. 
 
  private array(function(:void)) notify_funcs = ({}); 
  // Weak (when nonempty). 
 
  private array(function(Context:void)) prepare_funs; 
 
  /*private*/ array(function(Context:void)) get_prepare_funs() 
  { 
    if (prepare_funs) return prepare_funs; 
    array(function(Context:void)) funs = ({}); 
    for (int i = sizeof (imported) - 1; i >= 0; i--) 
      funs += imported[i]->get_prepare_funs(); 
    if (prepare_context) funs += ({prepare_context}); 
    // We don't cache in prepare_funs; do that only at the top level. 
    return funs; 
  } 
 
  string _sprintf() 
  { 
    return name ? "RXML.TagSet(" + name + ")" : "RXML.TagSet"; 
  } 
} 
 
TagSet empty_tag_set; 
//! The empty tag set. 
 
 
class Value 
//! Interface for objects used as variable values that are evaluated 
//! when referenced. 
{ 
  mixed rxml_var_eval (Context ctx, string var, string scope_name); 
} 
 
class Scope 
//! Interface for objects that emulates a scope mapping. 
{ 
  mixed `[] (string var, void|Context ctx, void|string scope_name) 
    {rxml_error ("Cannot query variable" + _in_the_scope (scope_name) + ".\n");} 
 
  mixed `[]= (string var, mixed val, void|Context ctx, void|string scope_name) 
    {rxml_error ("Cannot set variable" + _in_the_scope (scope_name) + ".\n");} 
 
  array(string) _indices (void|Context ctx, void|string scope_name) 
    {rxml_error ("Cannot list variables" + _in_the_scope (scope_name) + ".\n");} 
 
  void m_delete (string var, void|Context ctx, void|string scope_name) 
    {rxml_error ("Cannot delete variable" + _in_the_scope (scope_name) + ".\n");} 
 
  private string _in_the_scope (string scope_name) 
  { 
    if (scope_name) 
      if (scope_name != "") return " in the scope " + scope_name; 
      else return " in the current scope"; 
    else return ""; 
  } 
} 
 
#define SCOPE_TYPE mapping(string:mixed)|object(Scope) 
 
 
class Context 
//! A parser context. This contains the current variable bindings and 
//! so on. The current context can always be retrieved with 
//! get_context(). 
//! 
//! Note: Don't store pointers to this object since that will likely 
//! introduce circular references. It can be retrieved easily through 
//! get_context() or parser->context. 
{ 
  Frame frame; 
  //! The currently evaluating frame. 
 
  RequestID id; 
  //! 
 
  int type_check; 
  //! Whether to do type checking. 
 
  int error_count; 
  //! Number of RXML errors that has occurred. 
 
  TagSet tag_set; 
  //! The current tag set that will be inherited by subparsers. 
 
  int tag_set_is_local; 
  //! Nonzero if tag_set is a copy local to this context. A local tag 
  //! set that imports the old tag set is created whenever need be. 
 
  mixed get_var (string var, void|string scope_name) 
  //! Returns the value a variable in the specified scope, or the 
  //! current scope if none is given. Returns zero with zero_type 1 if 
  //! there's no such variable. 
  { 
    if (SCOPE_TYPE vars = scopes[scope_name || ""]) { 
      mixed val; 
      if (objectp (vars)) { 
        val = ([object(Scope)] vars)->`[] (var, this_object(), scope_name || ""); 
        if (val == Void) return ([])[0]; 
      } 
      else if (zero_type (val = vars[var])) return ([])[0]; 
      else if (objectp (val) && ([object] val)->rxml_var_eval) 
        return ([object(Value)] val)-> 
          rxml_var_eval (this_object(), var, scope_name || ""); 
      else return val; 
    } 
    else if (scope_name) rxml_error ("Unknown scope %O.\n", scope_name); 
    else rxml_error ("No current scope.\n"); 
  } 
 
  mixed set_var (string var, mixed val, void|string scope_name) 
  //! Sets the value of a variable in the specified scope, or the 
  //! current scope if none is given. Returns val. 
  { 
    if (SCOPE_TYPE vars = scopes[scope_name || ""]) 
      if (objectp (vars)) 
        return ([object(Scope)] vars)->`[]= (var, val, this_object(), scope_name || ""); 
      else 
        return vars[var] = val; 
    else if (scope_name) rxml_error ("Unknown scope %O.\n", scope_name); 
    else rxml_error ("No current scope.\n"); 
  } 
 
  void delete_var (string var, void|string scope_name) 
  //! Removes a variable in the specified scope, or the current scope 
  //! if none is given. 
  { 
    if (SCOPE_TYPE vars = scopes[scope_name || ""]) 
      if (objectp (vars)) 
        ([object(Scope)] vars)->m_delete (var, this_object(), scope_name || ""); 
      else 
        m_delete ([mapping(string:mixed)] vars, var); 
    else if (scope_name) rxml_error ("Unknown scope %O.\n", scope_name); 
    else rxml_error ("No current scope.\n"); 
  } 
 
  array(string) list_var (void|string scope_name) 
  //! Returns the names of all variables in the specified scope, or 
  //! the current scope if none is given. 
  { 
    if (SCOPE_TYPE vars = scopes[scope_name || ""]) 
      if (objectp (vars)) 
        return ([object(Scope)] vars)->_indices (this_object(), scope_name || ""); 
      else 
        return indices ([mapping(string:mixed)] vars); 
    else if (scope_name) rxml_error ("Unknown scope %O.\n", scope_name); 
    else rxml_error ("No current scope.\n"); 
  } 
 
  array(string) list_scopes() 
  //! Returns the names of all defined scopes. 
  { 
    return indices (scopes) - ({""}); 
  } 
 
  int exist_scope (void|string scope_name) 
  //! 
  { 
    return !!scopes[scope_name || ""]; 
  } 
 
  void add_scope (string scope_name, SCOPE_TYPE vars) 
  //! Adds or replaces the specified scope at the global level. A 
  //! scope can be an object. It must implement the methods `[], 
  //! _indices(), and m_delete(). 
  { 
    if (scopes[scope_name]) 
      if (scope_name == "") { 
        SCOPE_TYPE inner = scopes[""]; 
        while (SCOPE_TYPE outer = hidden[inner]) inner = outer; 
        hidden[inner] = vars; 
      } 
      else { 
        Frame outermost; 
        for (Frame f = frame; f; f = f->up) 
          if (f->scope_name == scope_name) outermost = f; 
        if (outermost) hidden[outermost] = vars; 
        else scopes[scope_name] = vars; 
      } 
    else scopes[scope_name] = vars; 
  } 
 
  void remove_scope (string scope_name) 
  //! Removes the named scope from the global level, if it exists. 
  { 
#ifdef MODULE_DEBUG 
    if (scope_name == "") error ("Cannot remove current scope.\n"); 
#endif 
    Frame outermost; 
    for (Frame f = frame; f; f = f->up) 
      if (f->scope_name == scope_name) outermost = f; 
    if (outermost) m_delete (hidden, outermost); 
    else m_delete (scopes, scope_name); 
  } 
 
  string current_scope() 
  //! Returns the name of the current scope, if it has any. 
  { 
    if (SCOPE_TYPE vars = scopes[""]) { 
      string scope_name; 
      while (scope_name = search (scopes, vars, scope_name)) 
        if (scope_name != "") return scope_name; 
    } 
    return 0; 
  } 
 
  void add_runtime_tag (Tag tag) 
  //! Adds a tag that will exist from this point forward in the 
  //! current context only. It will have effect in the current parser 
  //! and parent parsers up to the point where tag_set changes. 
  { 
    if (!new_runtime_tags) new_runtime_tags = RuntimeTags(); 
    new_runtime_tags->add_tags[tag] = 1; 
    // By doing the following, we can let remove_tags take precedence. 
    new_runtime_tags->remove_tags[tag] = 0; 
    new_runtime_tags->remove_tags[tag->name] = 0; 
  } 
 
  void remove_runtime_tag (string|Tag tag) 
  //! Removes a tag added by add_runtime_tag(). It will have effect in 
  //! the current parser and parent parsers up to the point where 
  //! tag_set changes. 
  { 
    if (!new_runtime_tags) new_runtime_tags = RuntimeTags(); 
    new_runtime_tags->remove_tags[tag] = 1; 
  } 
 
  void rxml_error (string msg, mixed... args) 
  //! Throws an RXML error with a dump of the parser stack. 
  { 
    if (sizeof (args)) msg = sprintf (msg, @args); 
    msg = rxml_errmsg_prefix + ": " + msg; 
    if (current_var) msg += " | &" + current_var + ";\n"; 
    for (Frame f = frame; f; f = f->up) { 
      if (f->tag) msg += " | <" + f->tag->name; 
      else if (!f->up) break; 
      else msg += " | <(unknown tag)"; 
      if (f->args) 
        foreach (sort (indices (f->args)), string arg) { 
          mixed val = f->args[arg]; 
          msg += " " + arg + "="; 
          if (arrayp (val)) msg += map (val, error_print_val) * ","; 
          else msg += error_print_val (val); 
        } 
      else msg += " (no argmap)"; 
      msg += ">\n"; 
    } 
    array b = backtrace(); 
    throw (({msg, b[..sizeof (b) - 2]})); 
  } 
 
  void handle_exception (mixed err, PCode|Parser evaluator) 
  //! This function gets any exception that is catched during 
  //! evaluation. evaluator is the object that catched the error. 
  { 
    error_count++; 
    string msg = describe_error (err); 
    if (msg[..sizeof (rxml_errmsg_prefix) - 1] == rxml_errmsg_prefix) { 
      // An RXML error. 
      while (evaluator->_parent) { 
        evaluator->error_count++; 
        evaluator = evaluator->_parent; 
      } 
      if (id && id->conf) 
        msg = ([function(mixed,Type:string)] 
               ([object] id->conf)->handle_rxml_error) (err, evaluator->type); 
      else { 
#ifdef MODULE_DEBUG 
      report_notice (describe_backtrace (err)); 
#else 
      report_notice (msg); 
#endif 
      } 
      if (evaluator->type->free_text && evaluator->report_error) 
        evaluator->report_error (msg); 
    } 
    else throw (err); 
  } 
 
  // Internals. 
 
  constant rxml_errmsg_prefix = "RXML parser error"; 
 
  private string error_print_val (mixed val) 
  { 
    if (arrayp (val)) return "array"; 
    else if (mappingp (val)) return "mapping"; 
    else if (multisetp (val)) return "multiset"; 
    else return sprintf ("%O", val); 
  } 
 
  string current_var; 
  // Used to get the parsed variable into the RXML error backtrace. 
 
  Parser new_parser (Type top_level_type) 
  // Returns a new parser object to start parsing with this context. 
  // Normally TagSet.`() should be used instead of this. 
  { 
#ifdef MODULE_DEBUG 
    if (in_use || frame) error ("Context already in use.\n"); 
#endif 
    return top_level_type->get_parser (this_object()); 
  } 
 
  mapping(string:SCOPE_TYPE) scopes = ([]); 
  // The variable mappings for every currently visible scope. A 
  // special entry "" points to the current local scope. 
 
  mapping(SCOPE_TYPE|Frame:SCOPE_TYPE) hidden = ([]); 
  // The currently hidden variable mappings in scopes. The old "" 
  // entries are indexed by the replacing variable mapping. The old 
  // named scope entries are indexed by the frame object which 
  // replaced them. 
 
  void enter_scope (Frame frame) 
  { 
    SCOPE_TYPE vars; 
#ifdef DEBUG 
    if (!frame->vars) error ("Internal error: Frame has no variables.\n"); 
#endif 
    if ((vars = [SCOPE_TYPE] frame->vars) != scopes[""]) { 
      hidden[vars] = scopes[""]; 
      scopes[""] = vars; 
      if (string scope_name = [string] frame->scope_name) { 
        hidden[frame] = scopes[scope_name]; 
        scopes[scope_name] = vars; 
      } 
    } 
  } 
 
  void leave_scope (Frame frame) 
  { 
    if (string scope_name = [string] frame->scope_name) 
      if (hidden[frame]) { 
        scopes[scope_name] = hidden[frame]; 
        m_delete (hidden, frame); 
      } 
    SCOPE_TYPE vars; 
    if (hidden[vars = [SCOPE_TYPE] frame->vars]) { 
      scopes[""] = hidden[vars]; 
      m_delete (hidden, vars); 
    } 
  } 
 
#define ENTER_SCOPE(ctx, frame) (frame->vars && ctx->enter_scope (frame)) 
#define LEAVE_SCOPE(ctx, frame) (frame->vars && ctx->leave_scope (frame)) 
 
  void make_tag_set_local() 
  { 
    if (!tag_set_is_local) { 
      TagSet new_tag_set = TagSet (tag_set->name + " (local)"); // FIXME: Cache this? 
      new_tag_set->imported = ({tag_set}); 
      tag_set = new_tag_set; 
      tag_set_is_local = 1; 
    } 
  } 
 
  class RuntimeTags 
  { 
    multiset(Tag) add_tags = (<>); 
    multiset(Tag|string) remove_tags = (<>); 
  } 
  RuntimeTags new_runtime_tags; 
  // Used to record the result of any add_runtime_tag() and 
  // remove_runtime_tag() calls since the last time the parsers ran. 
 
   void create (TagSet _tag_set, void|RequestID _id) 
  // Normally TagSet.`() should be used instead of this. 
  { 
    tag_set = _tag_set; 
    id = _id; 
  } 
 
  mapping(string:mixed)|mapping(object:array) unwind_state; 
  // If this is a mapping, we have an unwound stack state. It contains 
  // strings with arbitrary exception info, and the objects being 
  // unwound with arrays containing the extra state info they need. 
  // The first entry in these arrays are always the subobject. The 
  // special entries are: 
  // 
  // "top": ({Frame|Parser|PCode (top object)}) 
  // "stream_piece": mixed (When continuing, do a streaming 
  //  do_return() with this stream piece.) 
  // "exec_left": array (Exec array left to evaluate. Only used 
  //  between Frame._exec_array() and Frame._eval().) 
 
  string _sprintf() {return "RXML.Context";} 
 
#ifdef MODULE_DEBUG 
  int in_use; 
#endif 
} 
 
 
//! Current context. 
 
//! It's set before any function in RXML.Tag or RXML.Frame is called. 
 
#if constant (thread_create) 
private Thread.Local _context = thread_local(); 
inline void set_context (Context ctx) {_context->set (ctx);} 
inline Context get_context() {return [object(Context)] _context->get();} 
#else 
private Context _context; 
inline void set_context (Context ctx) {_context = ctx;} 
inline Context get_context() {return _context;} 
#endif 
 
#ifdef MODULE_DEBUG 
 
// Got races in this debug check, but looks like we have to live with that. :\ 
 
#define ENTER_CONTEXT(ctx)                                            \ 
  Context __old_ctx = get_context();                                    \ 
  set_context (ctx);                                                    \ 
  if (ctx) {                                                            \ 
    if (ctx->in_use && __old_ctx != ctx)                                \ 
      error ("Attempt to use context asynchronously.\n");               \ 
    ctx->in_use = 1;                                                    \ 
  } 
 
#define LEAVE_CONTEXT()                                                       \ 
  if (Context ctx = get_context())                                      \ 
    if (__old_ctx != ctx) ctx->in_use = 0;                              \ 
  set_context (__old_ctx); 
 
#else 
 
#define ENTER_CONTEXT(ctx)                                            \ 
  Context __old_ctx = get_context();                                    \ 
  set_context (ctx); 
 
#define LEAVE_CONTEXT()                                                       \ 
  set_context (__old_ctx); 
 
#endif 
 
void rxml_error (string msg, mixed... args) 
//! Tries to throw an error with rxml_error() in the current context. 
{ 
  Context ctx = get_context(); 
  if (ctx && ctx->rxml_error) 
    ctx->rxml_error (msg, @args); 
  else { 
    if (sizeof (args)) msg = sprintf (msg, @args); 
    msg = Context.rxml_errmsg_prefix + " (no context): " + msg; 
    array b = backtrace(); 
    throw (({msg, b[..sizeof (b) - 2]})); 
  } 
} 
 
 
//! Constants for the bit field RXML.Frame.flags. 
 
//! Static flags (i.e. tested in the Tag object). 
 
constant FLAG_CONTAINER = 0x00000001; 
//! If set, the tag accepts non-empty content. E.g. with the standard 
//! HTML parser this defines whether the tag is a container or not. 
 
constant FLAG_NO_PREFIX = 0x00000002; 
//! Never apply any prefix to this tag. 
 
//! The rest of the flags are dynamic (i.e. tested in the Frame object). 
 
constant FLAG_PARENT_SCOPE = 0x00000100; 
//! If set, the array from do_return() and cached_return() will be 
//! interpreted in the scope of the parent tag, rather than in the 
//! current one. 
 
constant FLAG_NO_IMPLICIT_ARGS = 0x00000200; 
//! If set, the parser won't apply any implicit arguments. FIXME: Not 
//! yet implemented. 
 
constant FLAG_STREAM_RESULT = 0x00000400; 
//! If set, the do_return() function will be called repeatedly until 
//! it returns 0 or no more content is wanted. 
 
constant FLAG_STREAM_CONTENT = 0x00000800; 
//! If set, the tag supports getting its content in streaming mode: 
//! do_return() will be called repeatedly with successive parts of the 
//! content then. Can't be changed from do_return(). 
 
//! Note: It might be obvious, but using streaming is significantly 
//! less effective than nonstreaming, so it should only be done when 
//! big delays are expected. 
 
constant FLAG_STREAM = FLAG_STREAM_RESULT | FLAG_STREAM_CONTENT; 
 
//! The following flags specifies whether certain conditions must be 
//! met for a cached frame to be considered (if RXML.Frame.is_valid() 
//! is defined). They may be read directly after do_return() returns. 
//! The tag name is always the same. FIXME: These are ideas only; not 
//! yet implemented. 
 
constant FLAG_CACHE_DIFF_ARGS = 0x00010000; 
//! If set, the arguments to the tag need not be the same (using 
//! equal()) as the cached args. 
 
constant FLAG_CACHE_DIFF_CONTENT = 0x00020000; 
//! If set, the content need not be the same. 
 
constant FLAG_CACHE_DIFF_RESULT_TYPE = 0x00040000; 
//! If set, the result type need not be the same. (Typically 
//! not useful unless cached_return() is used.) 
 
constant FLAG_CACHE_DIFF_VARS = 0x00080000; 
//! If set, the variables with external scope in vars (i.e. normally 
//! those that has been accessed with get_var()) need not have the 
//! same values (using equal()) as the actual variables. 
 
constant FLAG_CACHE_SAME_STACK = 0x00100000; 
//! If set, the stack of call frames needs to be the same. 
 
constant FLAG_CACHE_EXECUTE_RESULT = 0x00200000; 
//! If set, an array to execute will be stored in the frame instead of 
//! the final result. On a cache hit it'll be executed like the return 
//! value from do_return() to produce the result. 
 
 
class Frame 
//! A tag instance. 
{ 
  constant is_RXML_Frame = 1; 
  constant thrown_at_unwind = 1; 
 
  //! Interface. 
 
  Frame up; 
  //! The parent frame. This frame is either created from the content 
  //! inside the up frame, or it's in the array returned from 
  //! do_return() in the up frame. 
 
  Tag tag; 
  //! The RXML.Tag object this frame was created from. 
 
  int flags; 
  //! Various bit flags that affect parsing. See the FLAG_* constants. 
 
  mapping(string:mixed) args; 
  //! The arguments passed to the tag. Set before 
  //! do_enter()/do_return() are called. 
 
  Type content_type; 
  //! The type of the content. 
 
  mixed content = Void; 
  //! The content. Set before do_return() is called, but only when the 
  //! tag is actually used with container syntax. 
 
  Type result_type; 
  //! The required result type. Set before do_enter()/do_return() are 
  //! called. do_return() should produce a result of this type. 
 
  mixed result = Void; 
  //! The result. 
 
  //!mapping(string:mixed) vars; 
  //! Set this to introduce a new variable scope that will be active 
  //! during parsing of the content and return values (but see also 
  //! FLAG_PARENT_SCOPE). Don't replace or remove the mapping later. 
 
  //!string scope_name; 
  //! The scope name for the variables. Don't change this later. 
 
  //!TagSet additional_tags; 
  //! If set, the tags in this tag set will be used in addition to the 
  //! tags inherited from the surrounding parser. The additional tags 
  //! will in turn be inherited by subparsers. 
 
  //!TagSet local_tags; 
  //! If set, the tags in this tag set will be used in the parser for 
  //! the content, instead of the one inherited from the surrounding 
  //! parser. The tags are not inherited by subparsers. 
 
  optional int|function(RequestID:int|function) do_enter (RequestID id); 
  //! Called before the content (if any) is processed. This function 
  //! typically only initializes vars. Return values: 
  //! 
  //! int -   Do this many passes through the content. do_return() 
  //!         will be called after each pass. 
  //! function(RequestID:int|function) - A function that is handled 
  //!         just like do_enter(), only repeatedly until it returns 
  //!         0 or another function. 
  //! 
  //! If this function is missing, one pass is done. 
 
  //!array do_return (RequestID id, void|mixed piece); 
  //! Called after the content (if any) has been processed. 
  //! 
  //! The result_type variable is set to the type of result the parser 
  //! wants. It's any type that is valid by tag->result_type. If the 
  //! result type is sequential, it's spliced into the surrounding 
  //! content, otherwise it replaces the previous value of the 
  //! content, if any. 
  //! 
  //! Return values: 
  //! 
  //! array - A so-called execution array to be handled by the parser: 
  //! 
  //! string - Added or put into the result. If the result type has 
  //!         a parser, the string will be parsed with it before 
  //!         it's assigned to the result variable and passed on. 
  //! RXML.Frame - Already initialized frame to process. Neither 
  //!         arguments nor content will be parsed. It's result is 
  //!         added or put into the result of this tag. 
  //! mapping(string:mixed) - Fields to merge into the headers. 
  //!         FIXME: Not yet implemented. FIXME: Somehow represent 
  //!         removal of headers? 
  //! object - Treated as a file object to read in blocking or 
  //!         nonblocking mode. FIXME: Not yet implemented, details 
  //!         not decided. 
  //! multiset(mixed) - Should only contain one element that'll be 
  //!         added or put into the result. Normally not necessary; 
  //!         assign it directly to the result variable instead. 
  //! 
  //! 0 -     Do nothing special. Ends the stream when 
  //!         FLAG_STREAM_RESULT is set. 
  //! 
  //! Note that the intended use is not to postparse by returning 
  //! strings, but instead to return an array with literal strings and 
  //! RXML.Frame objects where parsing (or, more accurately, 
  //! evaluation) needs to be done. 
  //! 
  //! piece is used when the tag is operating in streaming mode (i.e. 
  //! FLAG_STREAM_CONTENT is set). It's then set to each successive 
  //! part of the content in the stream, and the content variable is 
  //! never touched. do_return() is also called "normally" with no 
  //! piece argument afterwards. Note that tags that support streaming 
  //! mode might still be used nonstreaming (it might also vary 
  //! between iterations). 
  //! 
  //! As long as FLAG_STREAM_RESULT is set, do_return() will be called 
  //! repeatedly until it returns 0. It's only the result piece from 
  //! the execution array that is propagated after each turn; the 
  //! result variable only accumulates all these pieces. 
  //! 
  //! If this function is an array, it's executed as above. If it's 
  //! zero, the value in the result variable is simply used. If the 
  //! result variable is Void, content is used as result if it's of a 
  //! compatible type. 
 
  //!int|function(:int) is_valid; 
  //! When defined, the frame may be cached. First the name of the tag 
  //! must be the same. Then the conditions specified by the cache 
  //! bits in flag are checked. Then, if this is a function, it's 
  //! called. If it returns 1, the frame is reused. FIXME: Not yet 
  //! implemented. 
 
  optional array cached_return (Context ctx, void|mixed piece); 
  //! If defined, this will be called to get the value from a cached 
  //! frame (that's still valid) instead of using the cached result. 
  //! It's otherwise handled like do_return(). Note that the cached 
  //! frame may be used from several threads. FIXME: Not yet 
  //! implemented. 
 
  //! Services. 
 
  void rxml_error (string msg, mixed... args) 
  //! Throws an RXML error from the current context. 
  { 
    get_context()/*HMM*/->rxml_error (msg, @args); 
  } 
 
  void terminate() 
  //! Makes the parser abort. The data parsed so far will be returned. 
  //! Does not return; throws a special exception instead. 
  { 
    error ("FIXME\n"); 
  } 
 
  void suspend() 
  //! Used together with resume() for nonblocking mode. May be called 
  //! from do_enter() or do_return() to suspend the parser: The parser 
  //! will just stop, leaving the context intact. If it returns, the 
  //! parser is used in a place that doesn't support nonblocking, so 
  //! just go ahead and block. 
  { 
    error ("FIXME\n"); 
  } 
 
  void resume() 
  //! Makes the parser continue where it left off. The function that 
  //! called suspend() will be called again. 
  { 
    error ("FIXME\n"); 
  } 
 
  // Internals. 
 
  mixed _exec_array (TagSetParser parser, array exec) 
  { 
    Frame this = this_object(); 
    Context ctx = parser->context; 
    int i = 0; 
    mixed res = Void; 
    Parser subparser = 0; 
 
    mixed err = catch { 
      if (flags & FLAG_PARENT_SCOPE) LEAVE_SCOPE (ctx, this); 
 
      for (; i < sizeof (exec); i++) { 
        mixed elem = exec[i], piece = Void; 
 
        switch (sprintf ("%t", elem)) { 
          case "string": 
            if (result_type->_parser_prog == PNone) 
              piece = elem; 
            else { 
              subparser = result_type->get_parser (ctx); 
              subparser->_parent = parser; 
              subparser->finish ([string] elem); // Might unwind. 
              piece = subparser->eval(); // Might unwind. 
              subparser = 0; 
            } 
            break; 
          case "object": 
            if (([object] elem)->is_RXML_Frame) { 
              ([object(Frame)] elem)->_eval (0); // Might unwind. 
              piece = ([object(Frame)] elem)->result; 
            } 
            else if (([object] elem)->is_RXML_Parser) { 
              // The subparser above unwound. 
              ([object(Parser)] elem)->finish(); // Might unwind. 
              piece = ([object(Parser)] elem)->eval(); // Might unwind. 
            } 
            else 
              error ("File objects not yet implemented.\n"); 
            break; 
          case "mapping": 
            error ("Header mappings not yet implemented.\n"); 
            break; 
          case "multiset": 
            if (sizeof ([multiset] elem) == 1) piece = ((array) elem)[0]; 
            else if (sizeof ([multiset] elem) > 1) 
              error (sizeof ([multiset] elem) + " values in multiset in exec array.\n"); 
            else error ("No value in multiset in exec array.\n"); 
            break; 
          default: 
            error ("Invalid type %t in exec array.\n", elem); 
        } 
 
        if (result_type->sequential) res += piece; 
        else if (piece != Void) result = res = piece; 
      } 
 
      if (result_type->sequential) result += res; 
      if (flags & FLAG_PARENT_SCOPE) ENTER_SCOPE (ctx, this); 
      return res; 
    }; 
 
    if (result_type->sequential) result += res; 
 
    if (objectp (err) && ([object] err)->thrown_at_unwind) { 
      mapping(string:mixed)|mapping(object:array) ustate; 
      if ((ustate = ctx->unwind_state) && !zero_type (ustate->stream_piece)) 
        // Subframe wants to stream. Update stream_piece and send it on. 
        if (result_type->sequential) 
          ustate->stream_piece = res + ustate->stream_piece; 
        else if (ustate->stream_piece == Void) 
          ustate->stream_piece = res; 
      ustate->exec_left = exec[i..]; // Left to execute. 
      if (subparser) 
        // Replace the string with the subparser object so that we'll 
        // continue in it later. It's done here to keep the original 
        // exec array untouched. 
        ([array] ustate->exec_left)[0] = subparser; 
    } 
    throw (err); 
  } 
 
  private void _handle_runtime_tags (TagSetParser parser, 
                                     Context.RuntimeTags runtime_tags) 
  { 
    // FIXME: PCode handling. 
    multiset(string|Tag) rem_tags = runtime_tags->remove_tags; 
    multiset(Tag) add_tags = runtime_tags->add_tags - rem_tags; 
    if (sizeof (rem_tags)) 
      foreach (indices (add_tags), Tag tag) 
        if (rem_tags[tag->name]) add_tags[tag] = 0; 
    array(string|Tag) arr_rem_tags = (array) rem_tags; 
    array(Tag) arr_add_tags = (array) add_tags; 
    for (Parser p = parser; p; p = p->_parent) 
      if (p->tag_set_eval) { 
        foreach (arr_add_tags, Tag tag) 
          ([object(TagSetParser)] p)->add_runtime_tag (tag); 
        foreach (arr_rem_tags, string|object(Tag) tag) 
          ([object(TagSetParser)] p)->remove_runtime_tag (tag); 
      } 
  } 
 
  void _eval (TagSetParser parser, 
              void|mapping(string:string) raw_args, 
              void|string raw_content) 
  // Note: It might be somewhat tricky to override this function. 
  { 
    Frame this = this_object(); 
    Context ctx = parser->context; 
 
    // Unwind state data: 
    //raw_content 
    int|function(RequestID:int|function) fn, iter; 
    Parser subparser; 
    mixed piece; 
    array exec; 
    int tags_added;         // Flag that we added additional_tags to ctx->tag_set. 
    //ctx->new_runtime_tags 
 
#define PRE_INIT_ERROR(X) (ctx->frame = this, error (X)) 
#ifdef DEBUG 
    // Internal sanity checks. 
    if (ctx != get_context()) 
      PRE_INIT_ERROR ("Internal error: Context not current.\n"); 
    if (!parser->tag_set_eval) 
      PRE_INIT_ERROR ("Internal error: Calling _eval() with non-tag set parser.\n"); 
#endif 
#ifdef MODULE_DEBUG 
    if (ctx->new_runtime_tags) 
      PRE_INIT_ERROR ("Looks like Context.add_runtime_tag() or " 
                      "Context.remove_runtime_tag() was used outside any parser.\n"); 
#endif 
 
    if (array state = ctx->unwind_state && ctx->unwind_state[this]) { 
#ifdef DEBUG 
      if (!up) 
        PRE_INIT_ERROR ("Internal error: Resuming frame without up pointer.\n"); 
      if (raw_args || raw_content) 
        PRE_INIT_ERROR ("Internal error: Can't feed new arguments or content " 
                        "when resuming parse.\n"); 
#endif 
      object ignored; 
      [ignored, fn, iter, raw_content, subparser, piece, exec, tags_added, 
       ctx->new_runtime_tags] = state; 
      m_delete (ctx->unwind_state, this); 
      if (!sizeof (ctx->unwind_state)) ctx->unwind_state = 0; 
    } 
    else { 
#ifdef MODULE_DEBUG 
      if (up && up != ctx->frame) 
        PRE_INIT_ERROR ("Reuse of frame in different context.\n"); 
#endif 
      up = ctx->frame; 
      piece = Void; 
    } 
 
#undef PRE_INIT_ERROR 
    ctx->frame = this; 
 
    if (raw_args) { 
      args = raw_args; 
      mapping(string:Type) atypes; 
      if (tag->req_arg_types) { 
        atypes = raw_args & tag->req_arg_types; 
        if (sizeof (atypes) < sizeof (tag->req_arg_types)) { 
          array(string) missing = sort (indices (tag->req_arg_types - atypes)); 
          rxml_error ("Required " + 
                      (sizeof (missing) > 1 ? 
                       "arguments " + String.implode_nicely (missing) + " are" : 
                       "argument " + missing[0] + " is") + " missing.\n"); 
        } 
      } 
      if (tag->opt_arg_types) 
        if (atypes) atypes += raw_args & tag->opt_arg_types; 
        else atypes = raw_args & tag->opt_arg_types; 
      if (atypes) 
        if (mixed err = catch { 
          foreach (indices (atypes), string arg) 
            args[arg] = atypes[arg]->eval ( 
              raw_args[arg], ctx, 0, parser, 1); // Should currently NOT unwind. 
        }) { 
          if (objectp (err) && ([object] err)->thrown_at_unwind) 
            error ("Can't save parser state when evaluating arguments.\n"); 
          throw (err); 
        } 
    } 
#ifdef DEBUG 
    if (!args) error ("Internal error: args not set.\n"); 
#endif 
 
    if (TagSet add_tags = raw_content && [object(TagSet)] this->additional_tags) { 
      if (!ctx->tag_set_is_local) ctx->make_tag_set_local(); 
      if (search (ctx->tag_set->imported, add_tags) < 0) { 
        ctx->tag_set->imported = ({add_tags}) + ctx->tag_set->imported; 
        tags_added = 1; 
      } 
    } 
 
    if (!result_type) { 
      Type ptype = parser->type; 
      foreach (tag->result_types, Type rtype) 
        if (ptype->subtype_of (rtype)) {result_type = rtype; break;} 
      if (!result_type)             // Sigh.. 
        rxml_error ( 
          "Tag returns " + 
          String.implode_nicely ([array(string)] tag->result_types->name, "or") + 
          " but " + [string] parser->type->name + " is expected.\n"); 
    } 
    if (!content_type) content_type = tag->content_type || result_type; 
 
    mixed err = catch { 
      if (!fn) fn = this->do_enter ? this->do_enter (ctx->id) : 1; // Might unwind. 
 
      do { 
        if (!iter) { 
          iter = fn, fn = 0; 
          while (functionp (iter)) { // Got a function from do_enter. 
            int|function(RequestID:int|function) newiter = 
              [int|function(RequestID:int|function)] iter (ctx->id); // Might unwind. 
            fn = iter, iter = newiter; 
          } 
        } 
        ENTER_SCOPE (ctx, this); 
        for (; iter > 0; iter--) { 
 
          if (raw_content) {    // Got nested parsing to do. 
            if (ctx->new_runtime_tags) { 
              // Empty this first in case do_enter() set it. 
              _handle_runtime_tags (parser, ctx->new_runtime_tags); 
              ctx->new_runtime_tags = 0; 
            } 
 
            int finished = 0; 
            if (!subparser) {   // The nested content is not yet parsed. 
              subparser = content_type->get_parser ( 
                ctx, [object(TagSet)] this->local_tags); 
              subparser->_parent = parser; 
              subparser->finish (raw_content); // Might unwind. 
              finished = 1; 
            } 
 
            do { 
              if (flags & FLAG_STREAM_CONTENT && subparser->read) { 
                // Handle a stream piece. 
                // Squeeze out any free text from the subparser first. 
                mixed res = subparser->read(); 
                if (content_type->sequential) piece = res + piece; 
                else if (piece == Void) piece = res; 
                if (piece != Void) { 
                  int|array|function(RequestID,void|mixed:array) do_return; 
                  if ((do_return = 
                       [int|array|function(RequestID,void|mixed:array)] 
                       this->do_return) && 
                      functionp (do_return)) { 
                    if (!exec) exec = do_return (ctx->id, piece); // Might unwind. 
                    if (exec) { 
                      mixed res = _exec_array (parser, exec); // Might unwind. 
                      if (flags & FLAG_STREAM_RESULT) { 
#ifdef DEBUG 
                      if (!zero_type (ctx->unwind_state->stream_piece)) 
                          error ("Internal error: " 
                                 "Clobbering unwind_state->stream_piece.\n"); 
#endif 
                      ctx->unwind_state->stream_piece = res; 
                        throw (this); 
                      } 
                      exec = 0; 
                    } 
                    else if (flags & FLAG_STREAM_RESULT) { 
                      // do_return() finished the stream. Ignore remaining content. 
                      ctx->unwind_state = 0; 
                      piece = Void; 
                      break; 
                    } 
                  } 
                  piece = Void; 
                } 
                if (finished) break; 
              } 
              else {            // The frame doesn't handle streamed content. 
                piece = Void; 
                if (finished) { 
                  mixed res = subparser->eval(); // Might unwind. 
                  if (content_type->sequential) content += res; 
                  else if (res != Void) content = res; 
                  break; 
                } 
              } 
 
              subparser->finish(); // Might unwind. 
              finished = 1; 
            } while (1); // Only loops when an unwound subparser has been recovered. 
            subparser = 0; 
          } 
 
          if (int|array|function(RequestID,void|mixed:array) do_return = 
              [int|array|function(RequestID,void|mixed:array)] this->do_return) { 
            if (!exec) 
              exec = functionp (do_return) ? 
                ([function(RequestID,void|mixed:array)] do_return) ( 
                  ctx->id) :        // Might unwind. 
                [array] do_return; 
            if (exec) { 
              mixed res = _exec_array (parser, exec); // Might unwind. 
              if (flags & FLAG_STREAM_RESULT) { 
#ifdef DEBUG 
              if (ctx->unwind_state) 
                  error ("Internal error: Clobbering unwind_state to do streaming.\n"); 
                if (piece != Void) 
                  error ("Internal error: Thanks, we think about how nice it must " 
                         "be to play the harmonica...\n"); 
#endif 
              ctx->unwind_state = (["stream_piece": res]); 
                throw (this); 
              } 
            } 
          } 
          else if (result == Void && content_type->subtype_of (result_type)) 
            result = content; 
 
        } 
      } while (fn); 
 
      if (ctx->new_runtime_tags) { 
        _handle_runtime_tags (parser, ctx->new_runtime_tags); 
        ctx->new_runtime_tags = 0; 
      } 
    }; 
 
    LEAVE_SCOPE (ctx, this); 
 
    if (err) { 
      string action; 
      if (objectp (err) && ([object] err)->thrown_at_unwind) { 
        mapping(string:mixed)|mapping(object:array) ustate = ctx->unwind_state; 
        if (!ustate) ustate = ctx->unwind_state = ([]); 
#ifdef DEBUG 
      if (ustate[this]) 
          error ("Internal error: Frame already has an unwind state.\n"); 
#endif 
 
        if (ustate->exec_left) { 
          exec = [array] ustate->exec_left; 
          m_delete (ustate, "exec_left"); 
        } 
 
        if (err == this || exec && sizeof (exec) && err == exec[0]) 
          // This frame or a frame in the exec array wants to stream. 
          if (parser->unwind_safe) { 
            // Rethrow to continue in parent since we've already done 
            // the appropriate do_return stuff in this frame in either 
            // case. 
            if (err == this) err = 0; 
            if (tags_added) { 
              ctx->tag_set->imported -= ({/*[object(TagSet)]HMM*/ this->additional_tags}); 
              tags_added = 0; 
            } 
            action = "break"; 
          } 
          else { 
            // Can't stream since the parser isn't unwind safe. Just 
            // continue. 
            m_delete (ustate, "stream_piece"); 
            action = "continue"; 
          } 
        else if (!zero_type (ustate->stream_piece)) { 
          // Got a stream piece from a subframe. We handle it above; 
          // store the state and tail recurse. 
          piece = ustate->stream_piece; 
          m_delete (ustate, "stream_piece"); 
          action = "continue"; 
        } 
        else action = "break";  // Some other reason - back up to the top. 
 
        ustate[this] = ({err, fn, iter, raw_content, subparser, piece, exec, tags_added, 
                         ctx->new_runtime_tags}); 
      } 
      else { 
        ctx->handle_exception (err, parser); // May throw. 
        action = "return"; 
      } 
 
      switch (action) { 
        case "break":           // Throw and handle in parent frame. 
#ifdef MODULE_DEBUG 
        if (!parser->unwind_state) 
            error ("Trying to unwind inside a parser that isn't unwind safe.\n"); 
#endif 
        throw (this); 
        case "continue":        // Continue in this frame through tail recursion. 
          _eval (parser); 
          return; 
        case "return":          // A normal return. 
          break; 
        default: 
          error ("Internal error: Don't you come here and %O on me!\n", action); 
      } 
    } 
 
    if (tags_added) 
      ctx->tag_set->imported -= ({/*[object(TagSet)]HMM*/ this->additional_tags}); 
    ctx->frame = up; 
  } 
 
  string _sprintf() 
  { 
    return "RXML.Frame(" + (tag && [string] tag->name) + ")"; 
  } 
} 
 
 
//! Parsers. 
 
 
class Parser 
//! Interface class for a syntax parser that scans, parses and 
//! evaluates an input stream. Access to a parser object is assumed to 
//! be done in a thread safe way except where noted. 
{ 
  constant is_RXML_Parser = 1; 
  constant thrown_at_unwind = 1; 
 
  //! Services. 
 
  int error_count; 
  //! Number of RXML errors that occurred during evaluation. If this 
  //! is nonzero, the value from eval() shouldn't be trusted. 
 
  function(Parser:void) data_callback; 
  //! A function to be called when data is likely to be available from 
  //! eval(). It's always called when the source stream closes. 
 
  //! write() and write_end() are the functions to use from outside 
  //! the parser system, not feed() or finish(). 
 
  int write (string in) 
  //! Writes some source data to the parser. Returns nonzero if there 
  //! might be data available in eval(). 
  { 
    int res; 
    ENTER_CONTEXT (context); 
    mixed err = catch { 
      if (context && context->unwind_state && context->unwind_state->top) { 
#ifdef MODULE_DEBUG 
      if (context->unwind_state->top != this_object()) 
          error ("The context got an unwound state from another parser. Can't rewind.\n"); 
#endif 
      m_delete (context->unwind_state, "top"); 
        if (!sizeof (context->unwind_state)) context->unwind_state = 0; 
      } 
      if (this_object()/*HMM*/->feed (in)) res = 1; // Might unwind. 
      if (res && data_callback) data_callback (this_object()); 
    }; 
    LEAVE_CONTEXT(); 
    if (err) 
      if (objectp (err) && ([object] err)->thrown_at_unwind) { 
#ifdef DEBUG 
      if (err != this_object()) 
          error ("Internal error: Unexpected unwind object catched.\n"); 
#endif 
      if (!context->unwind_state) context->unwind_state = ([]); 
        context->unwind_state->top = err; 
      } 
      else if (context) 
        context->handle_exception (err, this_object()); // May throw. 
      else throw (err); 
    return res; 
  } 
 
  void write_end (void|string in) 
  //! Closes the source data stream, optionally with a last bit of 
  //! data. 
  { 
    int res; 
    ENTER_CONTEXT (context); 
    mixed err = catch { 
      if (context && context->unwind_state && context->unwind_state->top) { 
#ifdef MODULE_DEBUG 
      if (context->unwind_state->top != this_object()) 
          error ("The context got an unwound state from another parser. Can't rewind.\n"); 
#endif 
      m_delete (context->unwind_state, "top"); 
        if (!sizeof (context->unwind_state)) context->unwind_state = 0; 
      } 
      this_object()/*HMM*/->finish (in); // Might unwind. 
      if (data_callback) data_callback (this_object()); 
    }; 
    LEAVE_CONTEXT(); 
    if (err) 
      if (objectp (err) && ([object] err)->thrown_at_unwind) { 
#ifdef DEBUG 
      if (err != this_object()) 
          error ("Internal error: Unexpected unwind object catched.\n"); 
#endif 
      if (!context->unwind_state) context->unwind_state = ([]); 
        context->unwind_state->top = err; 
      } 
      else if (context) 
        context->handle_exception (err, this_object()); // May throw. 
      else throw (err); 
  } 
 
  array handle_var (string varref) 
  // Parses and evaluates a possible variable reference, with the 
  // appropriate error handling. 
  { 
    // We're always evaluating here, so context is always set. 
    array(string) split = varref / "."; 
    if (sizeof (split) == 2) 
      if (mixed err = catch { 
        context->current_var = varref; 
        mixed val; 
        if (zero_type (val = context->get_var (split[1], split[0]))) { // May throw. 
          context->current_var = 0; 
          return ({}); 
        } 
        context->current_var = 0; 
        if (type->free_text) val = (string) val; 
        else return val == Void ? ({}) : ({val}); 
      }) { 
        context->current_var = 0; 
        context->handle_exception (err, this_object()); // May throw. 
        return ({}); 
      } 
    return type->free_text ? 0 : ({}); 
  } 
 
  //! Interface. 
 
  Context context; 
  //! The context to do evaluation in. It's assumed to never be 
  //! modified asynchronously during the time the parser is working on 
  //! an input stream. 
 
  Type type; 
  //! The expected result type of the current stream. (The parser 
  //! should not do any type checking on this.) 
 
  int compile; 
  //! Must be set to nonzero before a stream is fed which should be 
  //! compiled to p-code. 
 
  //!mixed unwind_safe; 
  //! If nonzero, the parser supports unwinding with throw()/catch(). 
  //! Whenever an exception is thrown from some evaluation function, 
  //! it should be able to call that function again with identical 
  //! arguments the next time it continues. 
 
  mixed feed (string in); 
  //! Feeds some source data to the parse stream. The parser may do 
  //! scanning and parsing before returning. If context is set, it may 
  //! also do evaluation in that context. Returns nonzero if there 
  //! could be new data to get from eval(). 
 
  void finish (void|string in); 
  //! Like feed(), but also finishes the parse stream. A last bit of 
  //! data may be given. It should work to call this on an already 
  //! finished stream if no argument is given to it. 
 
  optional void report_error (string msg); 
  //! Used to report errors to the end user through the output. This 
  //! is only called when the type allows free text. msg should be 
  //! stored in the output queue to be returned by eval(). 
 
  optional mixed read(); 
  //! Define to allow streaming operation. Returns the evaluated 
  //! result so far, but does not do any evaluation. Returns Void if 
  //! there's no data (for sequential types the empty value is also 
  //! ok). 
 
  mixed eval(); 
  //! Evaluates the data fed so far and returns the result. The result 
  //! returned by previous eval() calls should not be returned again 
  //! as (part of) this return value. Returns Void if there's no data 
  //! (for sequential types the empty value is also ok). 
 
  optional PCode p_compile(); 
  //! Define this to return a p-code representation of the current 
  //! stream, which always is finished. 
 
  optional void reset (Context ctx, Type type, mixed... args); 
  //! Define to support reuse of a parser object. It'll be called 
  //! instead of making a new object for a new stream. It keeps the 
  //! static configuration, i.e. the type. Note that this function 
  //! needs to deal with leftovers from add_runtime_tag() for 
  //! TagSetParser objects. 
 
  optional Parser clone (Context ctx, Type type, mixed... args); 
  //! Define to create new parser objects by cloning instead of 
  //! creating from scratch. It returns a new instance of this parser 
  //! with the same static configuration, i.e. the type. The instance 
  //! this function is called in is never actually used for parsing. 
 
  static void create (Context ctx, Type _type, mixed... args) 
  { 
    context = ctx; 
    type = _type; 
  } 
 
  // Internals. 
 
  Parser _next_free; 
  // Used to link together unused parser objects for reuse. 
 
  Parser _parent; 
  // The parent parser if this one is nested. 
 
  Stdio.File _source_file; 
  mapping _defines; 
  // These two are compatibility kludges for use with parse_rxml(). 
 
  string _sprintf() {return "RXML.Parser";} 
} 
 
 
class TagSetParser 
//! Interface class for parsers that evaluates using the tag set. It 
//! provides the evaluation and compilation functionality. The parser 
//! should call Tag._handle_tag() from feed() and finish() for every 
//! encountered tag, and Parser.handle_var() for encountered variable 
//! references. It must be able to continue cleanly after throw() from 
//! Tag._handle_tag(). 
{ 
  inherit Parser; 
 
  constant tag_set_eval = 1; 
 
  // Services. 
 
  mixed eval() {return this_object()/*HMM*/->read();} 
 
  // Interface. 
 
  TagSet tag_set; 
  //! The tag set used for parsing. 
 
  optional void reset (Context ctx, Type type, TagSet tag_set, mixed... args); 
  optional Parser clone (Context ctx, Type type, TagSet tag_set, mixed... args); 
  static void create (Context ctx, Type type, TagSet _tag_set, mixed... args) 
  { 
    ::create (ctx, type); 
    tag_set = _tag_set; 
  } 
  //! In addition to the type, the tag set is part of the static 
  //! configuration. 
 
  mixed read(); 
  //! Not optional. Since the evaluation is done in Tag._handle_tag() 
  //! or similar, this always does the same as eval(). 
 
  void add_runtime_tag (Tag tag); 
  //! Adds a tag that will exist from this point forward in the 
  //! current parser instance only. 
 
  void remove_runtime_tag (string|Tag tag); 
  //! Removes a tag added by add_runtime_tag(). 
 
  string _sprintf() {return "RXML.TagSetParser";} 
} 
 
class PNone 
//! The identity parser. It only returns its input. 
{ 
  inherit Parser; 
 
  string data = ""; 
  int evalpos = 0; 
 
  int feed (string in) 
  { 
    data += in; 
    return 1; 
  } 
 
  void finish (void|string in) 
  { 
    if (in) data += in; 
  } 
 
  string eval() 
  { 
    string res = data[evalpos..]; 
    evalpos = sizeof (data); 
    return res; 
  } 
 
  string byte_compile() 
  { 
    return data; 
  } 
 
  string byte_interpret (string byte_code, Context ctx) 
  { 
    return byte_code; 
  } 
 
  void reset (Context ctx) 
  { 
    context = ctx; 
    data = ""; 
    evalpos = 0; 
  } 
 
  string _sprintf() {return "RXML.PNone";} 
} 
 
 
mixed simple_parse (string in, void|program parser) 
//! A convenience function to parse a string with no type info, no tag 
//! set, and no variable references. The parser defaults to PExpr. 
{ 
  // FIXME: Recycle contexts? 
  return t_any (parser || PExpr)->eval (in, Context (empty_tag_set)); 
} 
 
 
//! Types. 
 
 
class Type 
//! A static type definition. It does type checking and specifies some 
//! properties of the type. It may also contain a Parser program that 
//! will be used to read text and evaluate values of this type. Note 
//! that the parser is not relevant for type checking. 
{ 
  constant is_RXML_Type = 1; 
 
  //! Interface. 
 
  //!string name; 
  //! Unique type identifier. Required and considered constant. Type 
  //! hierarchies are currently implemented with glob patterns, e.g. 
  //! "image/png" is a subtype of "image/*", and "array(string)" is a 
  //! subtype of "array(*)". 
 
  //!mixed sequential; 
  //! Nonzero if data of this type is sequential, defined as: 
  //! o  One or more data items can be concatenated with `+. 
  //! o  (Sane) parsers are homomorphic on the type, i.e. 
  //!     eval ("da") + eval ("ta") == eval ("da" + "ta") 
  //!    and 
  //!     eval ("data") + eval ("") == eval ("data") 
  //!  provided the data is only split between (sensibly defined) 
  //!  atomic elements. 
 
  //!mixed empty_value; 
  //! The empty value for sequential data types, i.e. what eval ("") 
  //! would produce. 
 
  //!mixed free_text; 
  //! Nonzero if the type keeps the free text between parsed tokens, 
  //! e.g. the plain text between tags in HTML. The type must be 
  //! sequential and use strings. 
 
  void type_check (mixed val); 
  //! Checks whether the given value is a valid one of this type. Type 
  //! errors are thrown with RXML.rxml_error(). 
 
  Type clone() 
  //! Returns a copy of the type. 
  { 
    Type newtype = object_program (this_object())(); 
    newtype->_parser_prog = _parser_prog; 
    newtype->_parser_args = _parser_args; 
    newtype->_t_obj_cache = _t_obj_cache; 
    return newtype; 
  } 
 
  //! Services. 
 
  int `== (mixed other) 
  //! 
  { 
    return objectp (other) && ([object] other)->is_RXML_Type && 
      ([object(Type)] other)->name == this_object()->name; 
  } 
 
  int subtype_of (Type other) 
  //! 
  { 
    return glob ([string] other->name, [string] this_object()->name); 
  } 
 
  Type `() (program/*(Parser)HMM*/ newparser, mixed... parser_args) 
  //! Returns a type identical to this one, but which has the given 
  //! parser. parser_args is passed as extra arguments to the 
  //! create()/reset()/clone() functions. 
  { 
    Type newtype; 
    if (sizeof (parser_args)) { // Can't cache this. 
      newtype = clone(); 
      newtype->_parser_prog = newparser; 
      newtype->_parser_args = parser_args; 
      if (newparser->tag_set_eval) newtype->_p_cache = ([]); 
    } 
    else { 
      if (!_t_obj_cache) _t_obj_cache = ([]); 
      if (!(newtype = _t_obj_cache[newparser])) 
        if (newparser == _parser_prog) 
          _t_obj_cache[newparser] = newtype = this_object(); 
        else { 
          _t_obj_cache[newparser] = newtype = clone(); 
          newtype->_parser_prog = newparser; 
          if (newparser->tag_set_eval) newtype->_p_cache = ([]); 
        } 
    } 
    return newtype; 
  } 
 
  inline Parser get_parser (Context ctx, void|TagSet tag_set) 
  //! Returns a parser instance initialized with the given context. 
  { 
    Parser p; 
    if (_p_cache) {             // It's a tag set parser. 
      TagSet tset; 
      // vvv Using interpreter lock from here. 
      PCacheObj pco = _p_cache[tset = tag_set || ctx->tag_set]; 
      if (pco && pco->tag_set_gen == tset->generation) { 
        if ((p = pco->free_parser)) { 
          pco->free_parser = p->_next_free; 
          // ^^^ Using interpreter lock to here. 
          p->data_callback = p->compile = 0; 
          p->reset (ctx, this_object(), tset, @_parser_args); 
        } 
        else 
          // ^^^ Using interpreter lock to here. 
          if (pco->clone_parser) 
            p = pco->clone_parser->clone (ctx, this_object(), tset, @_parser_args); 
          else if ((p = _parser_prog (ctx, this_object(), tset, @_parser_args))->clone) 
            // pco->clone_parser might already be initialized here due 
            // to race, but that doesn't matter. 
            p = (pco->clone_parser = p)->clone (ctx, this_object(), tset, @_parser_args); 
      } 
      else { 
        // ^^^ Using interpreter lock to here. 
        pco = PCacheObj(); 
        pco->tag_set_gen = tset->generation; 
        _p_cache[tset] = pco;   // Might replace an object due to race, but that's ok. 
        if ((p = _parser_prog (ctx, this_object(), tset, @_parser_args))->clone) 
          // pco->clone_parser might already be initialized here due 
          // to race, but that doesn't matter. 
          p = (pco->clone_parser = p)->clone (ctx, this_object(), tset, @_parser_args); 
      } 
    } 
    else { 
      if ((p = free_parser)) { 
        // Relying on interpreter lock here. 
        free_parser = p->_next_free; 
        p->data_callback = p->compile = 0; 
        p->reset (ctx, this_object(), @_parser_args); 
      } 
      else if (clone_parser) 
        // Relying on interpreter lock here. 
        p = clone_parser->clone (ctx, this_object(), @_parser_args); 
      else if ((p = _parser_prog (ctx, this_object(), @_parser_args))->clone) 
        // clone_parser might already be initialized here due to race, 
        // but that doesn't matter. 
        p = (clone_parser = p)->clone (ctx, this_object(), @_parser_args); 
    } 
    return p; 
  } 
 
  mixed eval (string in, void|Context ctx, void|TagSet tag_set, 
              void|Parser|PCode parent, void|int dont_switch_ctx) 
  //! Convenience function to parse and evaluate the value in the 
  //! given string. If a context isn't given, the current one is used. 
  //! The current context and ctx are assumed to be the same if 
  //! dont_switch_ctx is nonzero. 
  { 
    mixed res; 
    if (!ctx) ctx = get_context(); 
    if (_parser_prog == PNone) res = in; 
    else { 
      Parser p = get_parser (ctx, tag_set); 
      p->_parent = parent; 
      if (dont_switch_ctx) p->finish (in); // Optimize the job in p->write_end(). 
      else p->write_end (in); 
      res = p->eval(); 
      if (p->reset) 
        if (_p_cache) { 
          // Relying on interpreter lock in this block. 
          PCacheObj pco = _p_cache[tag_set || ctx->tag_set]; 
          p->_next_free = pco->free_parser; 
          pco->free_parser = p; 
        } 
        else { 
          // Relying on interpreter lock in this block. 
          p->_next_free = free_parser; 
          free_parser = p; 
        } 
    } 
    if (ctx->type_check) type_check (res); 
    return res; 
  } 
 
  // Internals. 
 
  program/*(Parser)HMM*/ _parser_prog = PNone; 
  // The parser to use. Should never be changed in a type object. 
 
  /*private*/ array(mixed) _parser_args = ({}); 
 
  /*private*/ mapping(program:Type) _t_obj_cache; 
  // To avoid creating new type objects all the time in `(). 
 
  // Cache used for parsers that doesn't depend on the tag set. 
  private Parser clone_parser;  // Used with Parser.clone(). 
  private Parser free_parser;   // The list of objects to reuse with Parser.reset(). 
 
  // Cache used for parsers that depend on the tag set. 
  private class PCacheObj 
  { 
    int tag_set_gen; 
    Parser clone_parser; 
    Parser free_parser; 
  } 
  /*private*/ mapping(TagSet:PCacheObj) _p_cache; 
 
  string _sprintf() {return "RXML.Type";} 
} 
 
 
static class TypeAny 
//! A completely unspecified nonsequential type. 
{ 
  inherit Type; 
  constant name = "*"; 
  string _sprintf() {return "RXML.t_any";} 
} 
TypeAny t_any = TypeAny(); 
 
static class TypeText 
//! The standard type for generic document text. 
{ 
  inherit Type; 
  constant name = "text/*"; 
  constant sequential = 1; 
  constant empty_value = ""; 
  constant free_text = 1; 
  string _sprintf() {return "RXML.t_text";} 
} 
TypeText t_text = TypeText(); 
 
static class TypeHtml 
//! The standard type for generic document text. 
{ 
  inherit TypeText; 
  constant name = "text/html"; 
  string _sprintf() {return "RXML.t_html";} 
} 
TypeHtml t_html = TypeHtml(); 
 
 
// P-code compilation and evaluation. 
 
class VarRef 
//! A helper for representing variable reference tokens. 
{ 
  constant is_RXML_VarRef = 1; 
  string scope, var; 
  static void create (string _scope, string _var) {scope = _scope, var = _var;} 
  int valid (Context ctx) {return ctx->exist_scope (scope);} 
  mixed get (Context ctx) {return ctx->get_var (var, scope);} 
  mixed set (Context ctx, mixed val) {return ctx->set_var (var, val, scope);} 
  void delete (Context ctx) {ctx->delete_var (var, scope);} 
  string name() {return scope + "." + var;} 
  string _sprintf() {return "RXML.VarRef(" + scope + "." + var + ")";} 
} 
 
class PCode 
//! Holds p-code and evaluates it. P-code is the intermediate form 
//! after parsing and before evaluation. 
{ 
  constant is_RXML_PCode = 1; 
  constant thrown_at_unwind = 1; 
 
  array p_code = ({}); 
 
  int error_count; 
  //! Number of RXML errors that occurred during evaluation. If this 
  //! is nonzero, the value from eval() shouldn't be trusted. 
 
  mixed eval (Context ctx) 
  //! Evaluates the p-code in the given context. 
  { 
    // FIXME 
  } 
 
  function(Context:mixed) compile(); 
  //! Returns a compiled function for doing the evaluation. The 
  //! function will receive a context to do the evaluation in. 
 
  string _sprintf() {return "RXML.PCode";} 
 
 
  // Internals. 
 
  void report_error (string msg) 
  { 
    // FIXME 
  } 
 
  PCode|Parser _parent; 
  // The parent evaluator if this one is nested. 
} 
 
 
//! Some parser tools. 
 
static class VoidType 
{ 
  mixed `+ (mixed... vals) {return sizeof (vals) ? predef::`+ (@vals) : this_object();} 
  mixed ``+ (mixed val) {return val;} 
  int `!() {return 1;} 
  string _sprintf() {return "RXML.Void";} 
}; 
VoidType Void = VoidType(); 
//! An object representing the void value. Works as initializer for 
//! sequences, since Void + anything == anything + Void == anything. 
 
class ScanStream 
//! A helper class for the input and scanner stage in a parser. It's a 
//! stream that takes unparsed strings and splits them into tokens 
//! which are queued. Intended to be inherited in a Parser class. 
{ 
  private class Link 
  { 
    array data; 
    Link next; 
  } 
  private Link head = Link();       // Last link is an empty eof marker. 
  private Link tail = head; 
  private int next_token = 0; 
  private string end = ""; 
  private int fin = 0; 
 
  array scan (string in, int finished); 
  //! The scanner function. It gets an unparsed string and should 
  //! return an array of tokens. If the second argument is nonzero, 
  //! there won't be any more data later. If the second argument is 
  //! zero, the last item in the returned array is handled as unparsed 
  //! data that will be passed back to the scanner later. Tokens may 
  //! be of any type. Use VarRef objects for variables. 
 
  void feed (string in) 
  //! 
  { 
#ifdef MODULE_DEBUG 
    if (fin) error ("Cannot feed data to a finished stream.\n"); 
#endif 
    array tokens = scan (end + in, 0); 
    end = [string] tokens[-1]; 
    if (sizeof (tokens) > 1) { 
      tail->data = tokens[..sizeof (tokens) - 2]; 
      tail = tail->next = Link(); 
    } 
  } 
 
  void finish (void|string in) 
  //! 
  { 
    if (in || !fin && sizeof (end)) { 
#ifdef MODULE_DEBUG 
      if (in && fin) error ("Cannot feed data to a finished stream.\n"); 
#endif 
      fin = 1; 
      if (in) end += in; 
      tail->data = scan (end, 1); 
      tail = tail->next = Link(); 
    } 
  } 
 
  void reset() 
  //! 
  { 
    head = Link(); 
    tail = head; 
    next_token = 0; 
    end = ""; 
    fin = 0; 
  } 
 
  mixed read() 
  //! Returns the next token, or Void if there's no more data. 
  { 
    while (head->next) 
      if (next_token >= sizeof (head->data)) { 
        next_token = 0; 
        head = head->next; 
      } 
      else return head->data[next_token++]; 
    return Void; 
  } 
 
  void unread (mixed... put_back) 
  //! Puts back tokens and variable references at the beginning of the 
  //! stream so that the leftmost argument will be read first. 
  { 
    int i = sizeof (put_back); 
    while (i) head->data[--next_token] = put_back[--i]; 
    if (i) { 
      Link l = Link(); 
      l->next = head, head = l; 
      l->data = allocate (next_token = max (i - 32, 0)) + put_back[..--i]; 
    } 
  } 
 
  array read_all() 
  //! 
  { 
    array data; 
    if (next_token) { 
      data = head->data[next_token..]; 
      head = head->next; 
      next_token = 0; 
    } 
    else data = ({}); 
    while (head->next) { 
      data += head->data; 
      head = head->next; 
    } 
    return data; 
  } 
 
  int finished() 
  //! Returns nonzero if the write end is finished. 
  { 
    return fin; 
  } 
 
  string _sprintf() {return "RXML.ScanStream";} 
} 
 
 
// Various internal stuff. 
 
// Argh! 
static program PHtml; 
static program PExpr; 
void _fix_module_ref (string name, mixed val) 
{ 
  mixed err = catch { 
    switch (name) { 
      case "PHtml": PHtml = [program] val; break; 
      case "PExpr": PExpr = [program] val; break; 
      case "empty_tag_set": empty_tag_set = [object(TagSet)] val; break; 
      default: error ("Herk\n"); 
    } 
  }; 
  if (err) werror (describe_backtrace (err)); 
}