using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Xml;

namespace System.Xml.Expression
{
  public class Xexpression
  {
    public static int debug_level = 0;

    public struct Name : IEquatable<Name>
    {
      private static NameTable nt = new NameTable ();

      private string name;

      public Name (string str)
	{
	  name = nt.Add (str);
	}

      public static implicit operator Name (string str)
      {
	return new Name (str);
      }

      public static implicit operator string (Name name)
      {
	return name.name;
      }

      public static bool operator== (Name n1, Name n2)
	{
	  return (object) n1.name == (object) n2.name;
	}

      public static bool operator!= (Name n1, Name n2)
	{
	  return (object) n1.name != (object) n2.name;
	}

      public static bool operator== (Name n1, string n2)
	{
	  return (object) n1.name == (object) n2;
	}

      public static bool operator!= (Name n1, string n2)
	{
	  return (object) n1.name != (object) n2;
	}

      public static bool operator== (string n1, Name n2)
	{
	  return (object) n1 == (object) n2.name;
	}

      public static bool operator!= (string n1, Name n2)
	{
	  return (object) n1 != (object) n2.name;
	}

      public bool Equals (Name name)
      {
	return Object.ReferenceEquals (this.name, name.name);
      }

      public override bool Equals (object obj)
      {
	return Object.ReferenceEquals (this.name, obj);
      }

      public override int GetHashCode ()
      {
	return name.GetHashCode ();
      }

      public static NameTable Table { get { return nt; } }

      public override string ToString () { return name; }
    }

    private static Name Nexpr = "expr";

    private static Name Nfuncall = "funcall";
    private static Name Nvarref = "varref";
    private static Name Ninteger = "integer";
    private static Name Nstring = "string";
    private static Name Nsymbol = "symbol";
    private static Name Nlist = "list";

    private static Name Ndefun = "defun";
    private static Name Nfname = "fname";
    private static Name Nargs = "args";
    private static Name Nargs_unevalled = "args-unevalled";
    private static Name Nfixed = "fixed";
    private static Name Noptional = "optional";
    private static Name Nrest = "rest";

    private static Name Ndefvar = "defvar";
    private static Name Nvname = "vname";
    private static Name Ndescription = "description";
    private static Name Nrange = "range";

    private static Name Nprogn = "progn";
    private static Name Nloop = "loop";
    private static Name Nfunction = "function";

    internal abstract class Function
    {
      public Name name;
      public int min_arg, max_arg;

      public Function () { }

      public Function (Name name, int min_arg, int max_arg)
      {
	this.name = name;
	this.min_arg = min_arg;
	this.max_arg = max_arg;
      }

      public abstract Term Call (Domain domain, Variable vari, Term[] args);

      public override string ToString ()
      {
	return name;
      }

      internal class Subroutine : Function
      {
	public Builtin builtin;
	public bool setvar;

	public Subroutine (Builtin builtin, Name name, bool setvar,
			   int min_arg, int max_arg)
	  : base (name, min_arg, max_arg)
	  {
	    this.builtin = builtin;
	  }

	public override Term Call (Domain domain, Variable vari, Term[] args)
	{
	  Term[] newargs = new Term[args.Length];

	  for (int i = 0; i < args.Length; i++)
	    newargs[i] = args[i].Eval (domain);
	  return builtin (domain, vari, newargs);
	}
      }

      internal class SpecialForm : Function
      {
	public Builtin builtin;

	public SpecialForm (Builtin builtin, Name name,
			    int min_arg, int max_arg)
	  : base (name, min_arg, max_arg)
	  {
	    this.builtin = builtin;
	  }

	public override Term Call (Domain domain, Variable vari, Term[] args)
	{
	  return builtin (domain, vari, args);
	}
      }

      internal class Lambda : Function
      {
	internal bool args_evalled;
	internal Variable[] args;
	internal Term[] body;

	public Lambda (XmlNode node, Domain domain)
	{
	  int nfixed = 0;
	  int noptional = 0;
	  int nrest = 0;
	  name = node.Attributes[Nfname].Value;
	    
	  node = node.FirstChild;
	  if (node != null
	      && (node.Name == Nargs || node.Name == Nargs_unevalled))
	    {
	      XmlNode n;
	      args_evalled = node.Name == Nargs;
	      for (n = node.FirstChild; n != null; n = n.NextSibling)
		{
		  if (n.Name == Nfixed)
		    nfixed++;
		  else if (n.Name == Noptional)
		    noptional++;
		  else if (n.Name == Nrest)
		    nrest++;
		  else
		    throw new Exception ("Invalid argument type: " + n);
		}
	      min_arg = nfixed;
	      max_arg = nfixed + noptional + nrest;
	      args = new Variable[max_arg];
	      n = node.FirstChild;
	      for (int i = 0; i < max_arg; n = n.NextSibling)
		args[i++] = domain.Defvar ((Name) n.Attributes[0].Value);
	      if (nrest == 1)
		max_arg = - max_arg;
	    }
	  else
	    {
	      min_arg = max_arg = 0;
	    }
	}

	public void SetBody (XmlNode node, Domain domain)
	{
	  for (node = node.FirstChild; node != null; node = node.NextSibling)
	    if (node.Name != Ndescription
		&& node.Name != Nargs
		&& node.Name != Nargs_unevalled)
	      break;
	  int nterms = 0;
	  for (XmlNode n = node; n != null; n = n.NextSibling)
	    nterms++;
	  if (nterms > 0)
	    {
	      body = new Term[nterms];
	      for (nterms = 0; node != null; node = node.NextSibling, nterms++)
		body[nterms] = new Term (node, domain);
	    }
	}

	public override Term Call (Domain domain, Variable vari, Term[] args)
	{
	  Bindings current = domain.bindings;
	  Term result = Zero;

	  try {
	    int i;
	    if (args_evalled)
	      {
		Term[] newargs = new Term[args.Length];
		for (i = 0; i < min_arg; i++)
		  newargs[i] = args[i].Eval (domain);
		args = newargs;
	      }
	    for (i = 0; i < min_arg; i++)
	      domain.Bind (this.args[i], args[i]);
	    if (body != null)
	      foreach (Term term in body)
		result = term.Eval (domain);
	  } finally {
	    domain.UnboundTo (current);
	  }
	  return result;
	}
      }
    }

    public abstract class Variable
    {
      public readonly Name name;
      internal Term val;

      public Variable (Name name, Term term)
      {
	this.name = name;
	Value = term;
      }

      public Term Value
      {
	get { return val; }
	set
	  {
	    if (! ValueP (value))
	      throw new Exception ("Invalid value of " + name + ": " + value);
	    val = value;
	  }
      }

      public abstract bool ValueP (Term term);

      public override string ToString () { return name + "(" + val + ")"; }

      internal class Int : Variable
      {
	public struct Range
	{
	  public int from, to;
	}

	public Range[] ranges;

	public Int (Name name, int i) : base (name, new Term (i)) { }

	public override bool ValueP (Term term)
	{
	  int i;

	  if (term.objval != null)
	    return false;
	  if (ranges == null)
	    return true;
	  i = term.intval;
	  foreach (Range r in ranges)
	    if (i >= r.from && i <= r.to)
	      return true;
	  return false;
	}
      }

      internal class Str : Variable
      {
	public string[] ranges;

	public Str (Name name, string str) : base (name, new Term (str)) { }

	public override bool ValueP (Term term)
	{
	  if (! (term.objval is string))
	    return false;
	  if (ranges == null)
	    return true;
	  string str = (string) term.objval;
	  foreach (string s in ranges)
	    if (s == str)
	      return true;
	  return false;
	}
      }

      internal class Misc : Variable
      {
	public Misc (Name name, Term term) : base (name, term) { }

	public override bool ValueP (Term term) { return true; }
      }
    }

    internal class Bindings
    {
      private Variable vari;
      private Term old_value;
      private Bindings next;
	
      private Bindings (Variable vari)
      {
	this.vari = vari;
	old_value = vari.val;
      }
	
      public static Bindings Bind (Bindings bindings, Variable vari, Term val)
      {
	Bindings b = new Bindings (vari);

	b.vari.Value = val;
	b.next = bindings;
	return b;
      }

      internal Bindings UnboundTo (Bindings boundary)
      {
	for (Bindings b = this; b != boundary; b = b.next)
	  b.vari.val = b.old_value;
	return boundary;
      }

      public override string ToString ()
      {
	string str = "(bindings";
	for (Bindings b = this; b != null; b = b.next)
	  str += " " + vari.name + "=" + b.old_value;
	return str + ")";
      }
    }

#if false
    internal class ThrowException : Exception
    {
      Name tag;
      public object value;

      public ThrowException (Name tag, object value) : base ()
	{
	  this.tag = tag;
	  this.value = value;
	}
    }
#endif

    internal struct CatchTag
    {
      public readonly Name name;
      public readonly int count;

      public CatchTag (Name name, int count)
	{
	  this.name = name;
	  this.count = count;
	}
    }

    public class Domain
    {
      public object context;
      public int depth = 0;

      internal Dictionary<Name, Function> functions;
      internal Dictionary<Name, Variable> variables;
      internal Bindings bindings;
      internal Stack<CatchTag> catch_list = new Stack<CatchTag> ();
      private int catch_count = 0;

      internal Domain ()
      {
	functions = new Dictionary<Name, Function> ();
	variables = new Dictionary<Name, Variable> ();
      }

      public Domain (object context) : this (basic, context)
      {
      }

      public Domain (Domain parent, object context)
      {
	functions = new Dictionary<Name, Function> (parent.functions);
	variables = new Dictionary<Name, Variable> (parent.variables);
	this.context = context;
      }

      internal void Bind (Variable vari, Term value)
      {
	bindings = Bindings.Bind (bindings, vari, value);
      }

      internal void UnboundTo (Bindings boundary)
      {
	if (bindings != null)
	  bindings = bindings.UnboundTo (boundary);
      }

      internal void Catch (Name name)
      {
	catch_list.Push (new CatchTag (name, catchcount++));
      }

      internal bool Catched {
	get { return catch_list.Peek ().count == catchcount; }
      }

      internal void ThrowReturn ()
      {
	CatchTag tag = catch_list.Peek ();
	while (tag.name != Nreturn)
	  {
	    catch_list.Pop ();
	    tag = catch_list.Peek ();
	  }
	catchcount = tag.count;
      }

      internal void ThrowBreak ()
      {
	catch_list.Peek ().count = catchcount;
      }

      internal void Uncatch ()
      {
	catch_list.Pop ();
      }

      public void DefSubr (Builtin builtin, string str, bool setvar,
			   int min_arg, int max_arg, params string[] aliases)
      {
	Name name = str;
	Function func = new Function.Subroutine (builtin, name, setvar,
						 min_arg, max_arg);
	functions[name] = func;
	foreach (string a in aliases)
	  functions[(Name) a] = func;
      }

      public void DefSpecial (Builtin builtin, string str,
			      int min_arg, int max_arg,
			      params string[] aliases)
      {
	Name name = str;
	Function func = new Function.SpecialForm (builtin, name,
						  min_arg, max_arg);
	functions[name] = func;
	foreach (string a in aliases)
	  functions[(Name) a] = func;
      }

      public void DefAlias (string alias, string str)
      {
	functions[(Name) alias] = functions[(Name) str];
      }

      internal Function.Lambda RegisterFunction (XmlNode node)
      {
	Function.Lambda lambda = new Function.Lambda (node, this);

	functions[lambda.name] = lambda;	
	return lambda;
      }

      internal Function Defun (XmlNode node)
      {
	Name name = node.Attributes[Nfname].Value;
	Function func;

	if (! functions.TryGetValue (name, out func))
	  func = RegisterFunction (node);
	((Function.Lambda) func).SetBody (node, this);
	return func;
      }

      public void Defvar (XmlNode node)
      {
	Name name = node.Attributes[0].Value;
	Variable vari;

	node = node.FirstChild;
	if (node.Name == Ndescription)
	  node = node.NextSibling;
	if (node != null)
	  {
	    Name type = node.Name;
	    XmlNodeList range_list = null;
	    int nranges = 0;
	    string val = node.InnerText;

	    node = node.NextSibling;
	    if (node != null)
	      {
		range_list = node.ChildNodes;
		nranges = range_list.Count;
	      }

	    if (type == Ninteger)
	      {
		Variable.Int vi = new Variable.Int (name, parse_integer (val));
		if (range_list != null)
		  {
		    vi.ranges = new Variable.Int.Range[nranges];

		    for (int i = 0; i < nranges; i++)
		      {
			XmlNode n = range_list[i];

			if (n.Name == Nrange)
			  {
			    vi.ranges[i].from =
			      parse_integer (n.FirstChild.InnerText);
			    vi.ranges[i].to =
			      parse_integer (n.LastChild.InnerText);
			  }
			else
			  {
			    int num = parse_integer (n.InnerText);
			    vi.ranges[i].from = vi.ranges[i].to = num;
			  }
		      }
		  }
		vari = vi;
	      }
	    else if (type == Nstring)
	      {
		Variable.Str vs = new Variable.Str (name, val);
		if (range_list != null)
		  vs.ranges = new string[nranges];
		for (int i = 0; i < nranges; i++)
		  vs.ranges[i] = range_list[i].Value;
		vari = vs;
	      }
	    else
	      throw new Exception ("Unknown type: " + type);
	  }
	else
	  vari = new Variable.Misc (name, Zero);
	variables[name] = vari;
      }

      internal Variable Defvar (Name name)
      {
	Variable vari = new Variable.Misc (name, Zero);
	variables[name] = vari;
	return vari;
      }

      internal Function GetFunc (Name name)
      {
	Function func;

	if (! functions.TryGetValue (name, out func))
	  throw new Exception ("Unknown function: " + name);
	return func;
      }

      public bool CopyFunc (Domain domain, Name name)
      {
	Function func = GetFunc (name);

	domain.functions[name] = func;
	return true;
      }

      public void CopyFunc (Domain domain)
      {
	foreach (KeyValuePair<Name, Function> kv in functions)
	  domain.functions[kv.Key] = kv.Value;
      }

      internal Variable GetVar (Name name)
      {
	Variable vari;

	if (! variables.TryGetValue (name, out vari))
	  variables[name] = vari = new Variable.Misc (name, Zero);
	return vari;
      }

      public override string ToString ()
      {
	string str = "<(functions";
	foreach (KeyValuePair<Name, Function> kv in functions)
	  str += " " + kv.Key;
	str += ") (variabls";
	foreach (KeyValuePair<Name, Variable> kv in variables)
	  str += " " + kv.Key;
	str += ")";
	if (bindings != null)
	  str += " " + bindings;
	if (context != null)
	  str += " (" + context + ")";
	str += ">";
	return str;
      }

      internal void DebugWrite (bool head, string fmt, params string[] arg)
      {
	if (debug_level > depth)
	  {
	    if (head)
	      {
		Console.WriteLine ();
		for (int i = 0; i < depth; i++)
		  Console.Write (" ");
	      }
	    Console.Write (fmt, arg);
	  }
      }
    }

    public delegate Term Builtin (Domain domain, Variable vari, Term[] args);

    private static Domain basic = new Domain ();

    internal static Function Fprogn;

    static Xexpression ()
    {
      basic.DefSubr (set_value, "set", true, 1, 1, "=");
      basic.DefSubr (not, "not", false, 1, 1, "!");
      basic.DefSubr (add, "add", true, 1, -1, "+");
      basic.DefSubr (mul, "mul", true, 1, -1, "*");
      basic.DefSubr (sub, "sub", true, 1, -1, "-");
      basic.DefSubr (div, "div", true, 1, -1, "/");
      basic.DefSubr (mod, "mod", true, 1, 2, "%");
      basic.DefSubr (logior, "logior", true, 1, -1, "|");
      basic.DefSubr (logand, "logand", true, 1, -1, "&");
      basic.DefSubr (lsh, "lsh", true, 1, 2, "<<");
      basic.DefSubr (rsh, "rsh", true, 1, 2, ">>");
      basic.DefSubr (eq, "eq", false, 2, -1, "==");
      basic.DefSubr (noteq, "noteq", false, 2, 2, "!=");
      basic.DefSubr (less_than, "lt", false, 2, -1, "<");
      basic.DefSubr (less_eq, "le", false, 2, -1, "<=");
      basic.DefSubr (greater_than, "gt", false, 2, -1, ">");
      basic.DefSubr (greater_eq, "ge", false, 2, -1, ">=");
      basic.DefSubr (append, "append", true, 0, -1);
      basic.DefSubr (concat, "concat", true, 0, -1);
      basic.DefSubr (nth, "nth", false, 2, 2);
      basic.DefSubr (copy, "copy", false, 1, 1);
      basic.DefSubr (ins, "ins", true, 2, 2);
      basic.DefSubr (del, "del", true, 2, 2);
      basic.DefSubr (eval_clause, "eval", false, 1, 1);
      basic.DefSubr (break_clause, "break", false, 0, 1);
      basic.DefSubr (return_clause, "return", false, 1, 1);
      basic.DefSpecial (and, "and", 1, -1, "&&");
      basic.DefSpecial (or, "or", 1, -1, "||");
      basic.DefSpecial (progn_clause, "progn", 0, -1, "expr");
      basic.DefSpecial (if_clause, "if", 2, 3);
      basic.DefSpecial (when_clause, "when", 1, -1);
      basic.DefSpecial (loop_clause, "loop", 1, -1);
      basic.DefSpecial (while_clause, "while", 1, -1);
      basic.DefSpecial (cond_clause, "cond", 1, -1);
      basic.DefSpecial (foreach_clause, "foreach", 2, -1);
      basic.DefSpecial (quote_clause, "quote", 1, 1);
      basic.DefSpecial (type_clause, "type", 1, 1);

      Fprogn = basic.GetFunc (Nprogn);
    }

    private static Term set_value (Domain domain, Variable vari, Term[] args)
    {
      vari.Value = args[0];
      return vari.val;
    }

    private static Term not (Domain domain, Variable vari, Term[] args)
    {
      return args[0].IsTrue ? Zero : One;
    }

    private static Term add (Domain domain, Variable vari, Term[] args)
    {
      int n = vari == null ? 0 : vari.val.Intval;

      foreach (Term arg in args)
	n += (int) arg;
      if (vari == null)
	return n;
      vari.val.intval = n;
      return vari.val;
    }

    private static Term mul (Domain domain, Variable vari, Term[] args)
    {
      int n = vari == null ? 1 : vari.val.Intval;
      foreach (Term arg in args)
	n *= (int) arg;
      if (vari == null)
	return n;
      vari.val.intval = n;
      return vari.val;
    }

    private static Term sub (Domain domain, Variable vari, Term[] args)
    {
      int n, i;

      if (vari == null)
	{
	  n = args[0].Intval;
	  i = 1;
	}
      else
	{
	  n = vari.val.Intval;
	  i = 0;
	}
      while (i < args.Length)
	n -= (int) args[i++];
      if (vari == null)
	return n;
      vari.val.intval = n;
      return vari.val;
    }

    private static Term div (Domain domain, Variable vari, Term[] args)
    {
      int n, i;

      if (vari == null)
	{
	  n = args[0].Intval;
	  i = 1;
	}
      else
	{
	  n = vari.val.Intval;
	  i = 0;
	}
      while (i < args.Length)
	n /= args[i++].Intval;
      if (vari == null)
	return n;
      vari.val.intval = n;
      return vari.val;
    }

    private static Term mod (Domain domain, Variable vari, Term[] args)
    {
      if (vari == null)
	return (args[0].Intval % args[1].Intval);
      vari.val.intval = vari.val.Intval % args[0].Intval;
      return vari.val;
    }

    private static Term logior (Domain domain, Variable vari, Term[] args)
    {
      int n = vari == null ? 0 : vari.val.Intval;
      foreach (Term arg in args)
	n |= (int) arg;
      if (vari == null)
	return n;
      vari.val.intval = n;
      return vari.val;
    }

    private static Term logand (Domain domain, Variable vari, Term[] args)
    {
      int n, i;

      if (vari == null)
	{
	  n = args[0].Intval;
	  i = 1;
	}
      else
	{
	  n = vari.val.Intval;
	  i = 0;
	}
      while (i < args.Length)
	n &= (int) args[i++];
      if (vari == null)
	return n;
      vari.val.intval = n;
      return vari.val;
    }

    private static Term lsh (Domain domain, Variable vari, Term[] args)
    {
      if (vari == null)
	return args[0].Intval << args[1].Intval;
      vari.val.intval = vari.val.Intval << args[0].Intval;
      return vari.val;
    }

    private static Term rsh (Domain domain, Variable vari, Term[] args)
    {
      if (vari == null)
	return args[0].Intval >> args[1].Intval;
      vari.val.intval = vari.val.Intval >> args[0].Intval;
      return vari.val;
    }

    private static Term eq (Domain domain, Variable vari, Term[] args)
    {
      Term o = args[0];

      if (o.objval == null)
	{
	  for (int i = 1; i < args.Length; i++)
	    if (args[i].objval != null || args[i].intval != o.intval)
	      return Zero;
	}
      else
	{
	  for (int i = 1; i < args.Length; i++)
	    if (o.objval.Equals (args[i].objval))
	      return Zero;
	}
      return One;
    }

    private static Term noteq (Domain domain, Variable vari, Term[] args)
    {
      return eq (domain, vari, args);
    }

    private static Term less_than (Domain domain, Variable vari, Term[] args)
    {
      int n = (int) args[0];

      for (int i = 1; i < args.Length; i++)
	{
	  int n1 = (int) args[i];
	  if (n >= n1)
	    return Zero;
	  n = n1;
	}
      return One;
    }

    private static Term less_eq (Domain domain, Variable vari, Term[] args)
    {
      int n = (int) args[0];
      for (int i = 1; i < args.Length; i++)
	{
	  int n1 = (int) args[i];
	  if (n > n1)
	    return Zero;
	  n = n1;
	}
      return One;
    }

    private static Term greater_than (Domain domain, Variable vari, Term[] args)
    {
      int n = (int) args[0];
      for (int i = 1; i < args.Length; i++)
	{
	  int n1 = (int) args[i];
	  if (n <= n1)
	    return Zero;
	  n = n1;
	}
      return One;
    }

    private static Term greater_eq (Domain domain, Variable vari, Term[] args)
    {
      int n = (int) args[0];
      for (int i = 1; i < args.Length; i++)
	{
	  int n1 = (int) args[i];
	  if (n < n1)
	    return Zero;
	  n = n1;
	}
      return One;
    }

    private static Term append (Domain domain, Variable vari, Term[] args)
    {
      List<Term> list;

      if (vari == null)
	list = new List<Term> ();
      else
	list = vari.val.Listval;

      foreach (Term arg in args)
	{
	  if (arg.IsList)
	    list.AddRange ((List<Term>) arg.objval);
	  else
	    list.Add (arg);
	}
      if (vari == null)
	{
	  Term result;
	  result.intval = 0;
	  result.objval = list;
	  return result;
	}
      vari.val.objval = list;
      return vari.val;
    }

    private static Term concat (Domain domain, Variable vari, Term[] args)
    {
      string str;

      if (vari == null)
	str = "";
      else
	str = vari.val.Strval;

      foreach (Term arg in args)
	{
	  if (arg.IsStr)
	    str += (string) arg.objval;
	  else if (arg.IsList)
	    foreach (Term term in (List<Term>) arg.objval)
	      str += (char) term.Intval;
	  else
	    str += (char) arg.Intval;
	}
      if (vari == null)
	{
	  Term result;
	  result.intval = 0;
	  result.objval = str;
	  return result;
	}
      vari.val.objval = str;
      return vari.val;
    }

    private static Term nth (Domain domain, Variable vari, Term[] args)
    {
      Term result;

      if (args[1].IsStr)
	{
	  result.intval = ((string) args[1].objval)[args[0].Intval];
	  result.objval = null;
	}
      else if (args[1].IsList)
	{
	  result = ((List<Term>) args[1].objval)[args[0].Intval];
	}
      else
	throw new Exception ("Term is not enumelable: " + args[1]);
      return result;
    }

    private static Term copy (Domain domain, Variable vari, Term[] args)
    {
      Term result;

      result.intval = 0;
      result.objval = new List<Term> (args[0].Listval);
      return result;
    }

    private static Term ins (Domain domain, Variable vari, Term[] args)
    {
      if (vari.val.IsStr)
	vari.val.objval
	  = vari.val.Strval.Insert (args[0].Intval, args[1].Strval);
      else if (vari.val.IsList)
	vari.val.Listval.InsertRange (args[0].Intval, args[1].Listval);
      else
	throw new Exception ("term is not collection: " + vari.val);
      return vari.val;
    }

    private static Term del (Domain domain, Variable vari, Term[] args)
    {
      if (vari.val.IsStr)
	vari.val.objval
	  = vari.val.Strval.Remove (args[0].Intval,
				    args[1].Intval - args[0].Intval);

      else if (vari.val.IsList)
	vari.val.Listval.RemoveRange (args[0].Intval,
				      args[1].Intval - args[0].Intval);
      else
	throw new Exception ("term is not collection: " + vari.val);
      return vari.val;
    }

    private static Term and (Domain domain, Variable vari, Term[] args)
    {
      foreach (Term arg in args)
	if (! arg.Eval (domain).IsTrue)
	  return Zero;
      return One;
    }

    private static Term or (Domain domain, Variable vari, Term[] args)
    {
      foreach (Term arg in args)
	if (arg.Eval (domain).IsTrue)
	  return One;
      return Zero;
    }

    private static Term eval_clause (Domain domain, Variable vari, Term[] args)
    {
      return (args[0].Eval (domain));
    }

    private static Term progn_clause (Domain domain, Variable vari, Term[] args)
    {
      Term result = One;

      foreach (Term arg in args)
	result = arg.Eval (domain);
      return result;
    }

    private static Term if_clause (Domain domain, Variable vari, Term[] args)
    {
      if (args[0].Eval (domain).IsTrue)
	return args[1].Eval (domain);
      if (args.Length == 2)
	return Zero;
      return args[2].Eval (domain);
    }

    private static Term when_clause (Domain domain, Variable vari, Term[] args)
    {
      if (! args[0].Eval (domain).IsTrue)
	return Zero;
      Term result = One;
      for (int i = 1; i < args.Length; i++)
	result = args[i].Eval (domain);
      return result;
    }

    private static Term break_clause (Domain domain, Variable vari, Term[] args)
    {
      Stack<CatchTag> clist = domain.catch_list;
      if (clist.Count == 0)
	throw new Exception ("No outer loop to break");
      CatchTag tag = clist.Peek ();
      if (tag.name != Nloop)
	throw new Exception ("No outer loop to break");
      domain.depth = tag.depth;
      return args.Length == 0 ? Zero : args[0];
    }	  

    private static Term return_clause (Domain domain, Variable vari, Term[] args)
    {
      Stack<CatchTag> clist = domain.catch_list;

      while (clist.Count > 0)
	{
	  CatchTag tag = clist.Pop ();
	  if (tag.name == Nfunction)
	    {
	      domain.depth = tag.depth;
	      return = args.Length == 0 ? Zero : args[0];
	    }
	}
      return args.Length == 0 ? Zero : args[0];
    }	  

    private static Term loop_clause (Domain domain, Variable vari, Term[] args)
    {
      domain.Catch (Nloop);
      Term result = Zero;
      try {
	while (! domain.Catched)
	  foreach (Term arg in args)
	    {
	      result = arg.Eval (domain);
	      if (domain.Catched)
		break;
	    }
      } finally {
	domain.Uncatch ();
      }
      return result;
    }

    private static Term while_clause (Domain domain, Variable vari, Term[] args)
    {
      while (args[0].Eval (domain).IsTrue)
	for (int i = 1; i < args.Length; i++)
	  args[i].Eval (domain);
      return Zero;
    }

    private static Term cond_clause (Domain domain, Variable vari, Term[] args)
    {
      foreach (Term arg in args)
	{
	  List<Term> list = arg.Listval;
	  Term result = list[0].Eval (domain);

	  if (result.IsTrue)
	    {
	      for (int i = 1; i < list.Count; i++)
		result = list[i].Eval (domain);
	      return result;
	    }
	}
      return Zero;
    }

    private static Term foreach_clause (Domain domain, Variable vari,
					Term[] args)
    {
      List<Term> list = args[0].Listval;
      Bindings current = domain.bindings;

      foreach (Term term in list)
	{
	  domain.Bind (vari, term);
	  try {
	    for (int i = 1; i < args.Length; i++)
	      args[i].Eval (domain);
	  } finally {
	    domain.UnboundTo (current);
	  }
	}
      return Zero;
    }

    private static Term quote_clause (Domain domain, Variable vari, Term[] args)
    {
      return new Term (args[0]);
    }

    private static Term type_clause (Domain domain, Variable vari, Term[] args)
    {
      if (args[0].IsInt)
	return TermInt;
      if (args[0].IsStr)
	return TermStr;
      if (args[0].IsName)
	return TermName;
      if (args[0].IsList)
	return TermList;
      return TermTerm;
    }

    public struct Term
    {
      public int intval;
      public object objval;

      public Term (int i) { intval = i; objval = null; }
      public Term (Name name) { intval = 0; objval = name; }
      public Term (string str) { intval = 0; objval = str; }
      public Term (List<Term> list) { intval = 0; objval = list; }
      public Term (Term term) { intval = 0; objval = term; }

      public Term (XmlNode node, Domain domain)
	{
	  Name name = node.Name;

	  if (name == Ninteger)
	    {
	      intval = parse_integer (node.InnerText);
	      objval = null;
	    }
	  else
	    {
	      intval = 0;
	      if (name == Nsymbol)
		objval = (Name) node.InnerText;
	      else if (name == Nstring)
		objval = node.InnerText.Clone ();
	      else if (name == Nvarref)
		objval = domain.GetVar ((Name) node.Attributes[0].Value);
	      else if (name == Nlist)
		{
		  List<Term> list = new List<Term> ();
		  for (node = node.FirstChild; node != null;
		       node = node.NextSibling)
		    list.Add (new Term (node, domain));
		  objval = list;
		}
	      else
		{
		  Function func;
		  Variable vari = null;
		  Term[] args;

		  if (name == Nfuncall)
		    name = node.Attributes[0].Value;
		  else if (node.Attributes[Nvname] != null)
		    vari = domain.GetVar (node.Attributes[Nvname].Value);
		  func = domain.GetFunc (name);
		  XmlNodeList nlist = node.ChildNodes;
		  int nargs = nlist.Count;

		  if (nargs < func.min_arg
		      || (func.max_arg >= 0 && nargs > func.max_arg))
		    throw new Exception ("Invalid number of arguments to: "
					 + name + " " + nargs);
		  args = new Term[nargs];
		  for (int i = 0; i < nlist.Count; i++)
		    args[i] = new Term (nlist[i], domain);
		  objval = new Funcall (func, vari, args);
		}
	    }
	}

      private class Funcall
      {
	internal Function func;
	internal Variable vari;
	internal Term[] args;

	public Funcall (Function func, Variable vari, Term[] args)
	{
	  this.func = func;
	  this.vari = vari;
	  this.args = args;
	}

	public Term Eval (Domain domain)
	{
	  domain.DebugWrite (true, "(({0}", func.name);
	  for (int i = 0; i < args.Length; i++)
	    domain.DebugWrite (false, " {0}", args[i].ToString ());
	  domain.DebugWrite (false, ")");
	  domain.depth++;
	  Term result = func.Call (domain, vari, args);
	  domain.depth--;
	  domain.DebugWrite (true, " ==> {0})", result.ToString ());
	  return result;
	}

	public override string ToString ()
	{
	  string str = "<funcall fname=\"" + func.name;
	  if (args == null)
	    return str + "\"/>";
	  str += "\">";
	  foreach (Term e in args)
	    str += e;
	  return (str + "</funcall>");
	}
      }

      public int Intval {
	get {
	  if (objval != null)
	    throw new Exception ("term is not integer: " + this);
	  return intval;
	}
      }

      public string Strval {
	get {
	  if (! IsStr)
	    throw new Exception ("term is not string: " + this);
	  return (string) objval;
	}
      }

      public List<Term> Listval {
	get {
	  if (! IsList)
	    throw new Exception ("term is not list: " + this);
	  return (List<Term>) objval;
	}
      }

      public bool IsTrue {
	get {
	  return (objval == null
		  ? (intval != 0)
		  : objval is List<Term>
		  ? (((List<Term>) objval).Count != 0)
		  : true);
	}
      }
      public bool IsInt { get { return (objval == null); } }
      public bool IsStr { get { return (objval is string); } }
      public bool IsName { get { return (objval is Name); } }
      public bool IsList { get { return (objval is List<Term>); } }

      public Term Eval (Domain domain)
      {
	if (objval == null || objval is Name || objval is string)
	  return this;
	if (objval is List<Term>)
	  return new Term ((List<Term>) objval);
	if (objval is Funcall)
	  return ((Funcall) objval).Eval (domain);
	if (objval is Variable)
	  return ((Variable) objval).val;
	if (objval is Term)
	  return (Term) objval;
	throw new Exception ("invalid Term object: " + objval);
      }

      public static explicit operator int (Term term)
      {
	if (term.objval != null)
	  throw new Exception ("Not an integer term: " + term);
	return term.intval;
      }

      public static explicit operator Name (Term term)
      {
	return (Name) term.objval;
      }

      public static implicit operator Term (int i)
      {
	return new Term (i);
      }

      public override string ToString ()
      {
	string str;

	if (objval == null)
	  str = "<integer>" + intval + "</integer>";
	else if (objval is Name)
	  str = "<symbol>" + objval + "</symbol>";
	else if (objval is string)
	  str = "<string>" + objval + "</string>";
	else if (objval is List<Term>)
	  {
	    str = "<list>";
	    foreach (Term e in (List<Term>) objval)
	      str += e;
	    str += "</list>";
	  }
	else if (objval is Funcall)
	  str = "<funcall fname=\"" + ((Funcall) objval).func.name + "\"/>";
	else if (objval is Variable)
	  str = "<variable vname=\"" + ((Variable) objval).name + "\"/>";
	else if (objval is Term)
	  str = "<quote>" + objval + "</quote>";
	else
	  throw new Exception ("invalid Term object: " + objval);
	return str;
      }
    }

    static Term Zero = new Term (0);
    static Term One = new Term (1);
    static Term TermInt = new Term (Ninteger);
    static Term TermStr = new Term (Nstring);
    static Term TermName = new Term (Nsymbol);
    static Term TermList = new Term (Nlist);
    static Term TermTerm = new Term ((Name) "term");

    internal static int parse_integer (string str)
    {
      int len = str.Length;
      bool negative = false;

      if (len <= 1)
	return (len == 0 ? 0 : str[0] - '0');

      int c = str[0];
      int i;

      if (c == '0' && str[1] == 'x')
	{
	  i = 0;
	  for (int idx = 2; idx < len; idx++)
	    {
	      c = str[idx];
	      if (c < '0')
		break;
	      else if (c <= '9')
		i = i * 16 + (c - '0');
	      else if (c < 'A')
		break;
	      else if (c <= 'F')
		i = i * 16 + (c - 'A');
	      else if (c < 'a')
		break;
	      else if (c <= 'f')
		i = i * 16 + (c - 'a');
	      else
		break;
	    }
	  return i;
	}
      if (c == '-')
	negative = true;
      i = c - '0';
      for (int idx = 1; idx < len; idx++)
	{
	  c = str[idx];
	  if (c < '0' || c > '9')
	    break;
	  i = i * 10 + (c - '0');
	}
      return negative ? - i : i;
    }

    private Term[] terms;

    public Xexpression (string url, Domain domain)
    {
      XmlDocument doc = new XmlDocument (Name.Table);
      XmlNode node;

      using (XmlTextReader reader = new XmlTextReader (url, Name.Table))
	{
	  do {
	    reader.Read ();
	  } while (reader.NodeType != XmlNodeType.None
		   && (reader.NodeType != XmlNodeType.Element
		       || reader.Name != Nexpr));
	  if (reader.NodeType == XmlNodeType.None)
	    throw new Exception ("Node <expr> not found");
	  node = doc.ReadNode (reader);
	}

      int nterms = 0;
      for (XmlNode n = node.FirstChild; n != null; n = n.NextSibling)
	if (n.NodeType == XmlNodeType.Element)
	  {
	    if (n.Name == Ndefun)
	      domain.RegisterFunction (n);
	    else if (n.Name == Ndefvar)
	      domain.Defvar (n);
	    else
	      nterms++;
	  }

      terms = new Term[nterms];
      int i = 0;
      for (XmlNode n = node.FirstChild; n != null; n = n.NextSibling)
	if (n.NodeType == XmlNodeType.Element)
	  {
	    if (n.Name == Ndefun)
	      domain.Defun (n);
	    else if (n.Name != Ndefvar)
	      terms[i++]= new Term (n, domain);
	  }
    }

    public Term Eval (Domain domain)
    {
      Term result = Zero;

      domain.depth = 0;
      foreach (Term term in terms)
	result = term.Eval (domain);
      return result;
    }

    public override string ToString ()
    {
      string str = "";
      for (int i = 0; i < terms.Length; i++)
	str += terms[i];
      return str;
    }
  }
}