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

namespace System.Xml.Expression
{
  public class Xex
  {
    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 Ntype = "type";

    private static Name Ninteger = "integer";
    private static Name Nstring = "string";
    private static Name Nboolean = "boolean";
    private static Name Nsymbol = "symbol";
    private static Name Nlist = "list";
    private static Name Nobject = "object";

    private static Name Ndefun = "defun";
    private static Name Nfname = "fname";
    private static Name Nargs = "args";
    private static Name Noptional = "optional";
    private static Name Nrest = "rest";
    private static Name Nbody = "body";

    private static Name Ndefvar = "defvar";
    private static Name Nconst = "const";
    private static Name Nvariable = "variable";
    private static Name Ndescription = "description";
    private static Name Npossible_value = "possible-value";

    private static Name Nfuncall = "funcall";
    private static Name Nprogn = "progn";

    internal class Function
    {
      internal class Lambda
      {
	internal Xex[] args;
	internal Xex[] body;

	public void SetArgs (XmlNode node, int nargs, Domain domain)
	{
	  args = new Xex[nargs];
	  node = node.FirstChild;
	  for (int i = 0; i < nargs; node = node.NextSibling)
	    if (node.Name != Noptional && node.Name != Nrest)
	      args[i++] = new Xex (node, domain);
	}

	public void SetBody (XmlNode node, Domain domain)
	{
	  XmlNodeList nlist = node.ChildNodes;

	  body = new Xex[nlist.Count];
	  for (int i = 0; i < nlist.Count; i++)
	    body[i] = new Xex (nlist[i], domain);
	}
      }

      public readonly Name name;
      public Builtin builtin;
      public int min_arg, max_arg;
      internal Lambda lambda;
      public bool specialp = false;

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

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

      public void Setup (XmlNode node, Domain domain)
      {
	lambda = new Lambda ();
	node = node.FirstChild;
	if (node.Name == Nargs)
	  {
	    lambda.SetArgs (node, max_arg, domain);
	    node = node.NextSibling;
	  }
	if (node.Name == Nbody)
	  lambda.SetBody (node, domain);
      }

      public static Name ParseHead (XmlNode node,
				    out int min_arg, out int max_arg)
      {
	Name name = node.Attributes[Nfname].Value;
	int nargs = 0, noptions = 0, nrest = 0;
	XmlNode n;
	    
	for (n = node.FirstChild; n != null; n = n.NextSibling)
	  {
	    if (n.Name == Noptional || n.Name == Nrest)
	      break;
	    nargs++;
	  }
	if (n != null && n.Name == Noptional)
	  for (n = n.NextSibling; n != null; n = n.NextSibling)
	    {
	      if (n.Name == Nrest)
		break;
	      noptions++;
	    }
	if (n != null && n.Name == Nrest)
	  for (n = n.NextSibling; n != null; n = n.NextSibling)
	    nrest++;
	min_arg = nargs;
	max_arg = nargs + noptions + nrest;
	if (nrest == 1)
	  max_arg = - max_arg;
	return name;
      }

      public object Call (Xex[] args, Domain domain)
      {
	Bindings current = domain.bindings;
	object result = false;

	Console.Write ("calling (" + this);
	try {
	  foreach (Xex e in args)
	    Console.Write (" " + e);
	  Console.Write (") => ");
	  if (builtin != null)
	    {
	      if (! specialp)
		foreach (Xex a in args)
		  if (a.Eval (domain) == null)
		    throw new Exception ("evaled to null");
	      result = builtin (args, domain);
	      Console.WriteLine (result);
	      return result;
	    }

	  int i;
	  for (i = 0; i < min_arg; i++)
	    {
	      Xex a = lambda.args[i];
	      bool isdirect = a.args == null;
	      Name name = isdirect ? (Name) a.val : (Name) a.args[0].val;
	      Variable var = new VarMisc (name, null);

	      domain.variables[name] = var;
	      if (isdirect)
		domain.Bind (var, args[i]);
	      else
		domain.Bind (var, args[i].Eval (domain));
	    }
	  foreach (Xex e in lambda.body)
	    result = e.Eval (domain);
	  Console.WriteLine (result);
	} finally {
	  domain.UnboundTo (current);
	}
	return result;
      }

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

    internal abstract class Variable
    {
      public readonly Name name;
      public readonly Name type;
      internal object val;

      public Variable (Name name, Name type, object value)
      {
	if (value != null)
	  Value = value;
	this.name = name;
	this.type = type;
      }

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

      public abstract bool ValueP (object value);

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

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

      public Range[] ranges;

      public VarInt (Name name, object value) : base (name, Ninteger, value) { }

      public override bool ValueP (object value)
      {
	int i;

	if (! (value is int))
	  return false;
	if (ranges == null)
	  return true;
	i = (int) value;
	foreach (Range r in ranges)
	  if (i >= r.from && i <= r.to)
	    return true;
	return false;
      }
    }

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

      public VarStr (Name name, object value) : base (name, Nstring, value) { }

      public override bool ValueP (object value)
      {
	string str;

	if (! (value is string))
	  return false;
	if (ranges == null)
	  return true;
	str = (string) value;
	foreach (string s in ranges)
	  if (s == str)
	    return true;
	return false;
      }
    }

    internal class VarBool : Variable
    {
      public VarBool (Name name, object value)
	: base (name, Nboolean, value) { }

      public override bool ValueP (object value)
      {
	if (! (value is bool))
	  return false;
	return true;
      }
    }

    internal class VarMisc : Variable
    {
      public VarMisc (Name name, object value) : base (name, Nobject, value) { }

      public override bool ValueP (object value)
      {
	return true;
      }
    }

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

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

      internal Bindings UnboundTo (Bindings boundary)
      {
	for (Bindings b = this; b != boundary; b = b.next)
	  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;
	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

    public class Domain
    {
      public object context;

      internal Dictionary<Name, Function> functions;
      internal Dictionary<Name, Variable> variables;
      internal Bindings bindings;

      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, object value)
      {
	bindings = Bindings.Bind (bindings, vari, value);
      }

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

      public void Defun (Name name, Builtin builtin, int min_arg, int max_arg)
      {
	Defun (name, builtin, min_arg, max_arg, false);
      }

      public void Defun (Name name, Builtin builtin,
			 int min_arg, int max_arg, bool specialp)
      {
	Function func;

	if (functions.TryGetValue (name, out func))
	  {
	    if (func.min_arg < min_arg || func.max_arg > max_arg)
	      throw new Exception ("Incompatible argument numbers to override: "
				   + name);
	    func.builtin = builtin;
	    func.lambda = null;
	    func.min_arg = min_arg;
	    func.max_arg = max_arg;
	    func.specialp = specialp;
	  }
	else
	  {
	    functions[name]
	      = new Function (name, builtin, min_arg, max_arg, specialp);
	  }
      }

      internal Function RegisterFunction (XmlNode node)
      {
	int min_arg, max_arg;
	Name name = Function.ParseHead (node, out min_arg, out max_arg);
	Function func = new Function (name, min_arg, max_arg);

	functions[name] = func;	
	return func;
      }

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

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

      public void Defvar (Name name, XmlNode node)
      {
	Variable vari;

	if (node.Name == Ndescription)
	  node = node.NextSibling;
	if (node.Name == Nconst)
	  {
	    Name type = (Name) node.Attributes[Ntype].Value;
	    string val = node.Value;
	    XmlNodeList range_list = null;
	    int nranges = 0;

	    node = node.NextSibling;
	    if (node.Name == Npossible_value)
	      {
		range_list = node.ChildNodes;
		nranges = range_list.Count;
	      }

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

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

			if (n.Name == Nconst)
			  {
			    int num = parse_integer (n.Value);
			    vi.ranges[i].from = vi.ranges[i].to = num;
			  }
			else	// range_list[i].Name == "range"
			  {
			    vi.ranges[i].from =
			      parse_integer (n.FirstChild.Value);
			    vi.ranges[i].to =
			      parse_integer (n.LastChild.Value);
			  }
		      }
		  }
		vari = vi;
	      }
	    else if (type == Nstring)
	      {
		VarStr vs = new VarStr (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 if (type == Nboolean)
	      {
		vari = new VarBool (name, val == "true");
	      }
	    else
	      throw new Exception ("Unknown type: " + type);
	  }
	else
	  vari = new VarMisc (name, null);
	variables[name] = 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 VarMisc (name, null);
	return vari;
      }

      internal Variable GetVar (Xex e)
      {
	if (! (e.val is Name))
	  throw new Exception ("Not a symbol" + e.val);
	return GetVar ((Name) e.val);
      }

      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;
      }
    }

    public delegate object Builtin (Xex[] args, Domain domain);

    private static Domain basic = new Domain ();

    internal static Function Fprogn;

    static Xex ()
    {
      basic.Defun ("set", set_value, 2, 2, false);
      basic.Defun ("=", set_value, 2, 2, false);
      basic.Defun ("and", and, 1, -1, false);
      basic.Defun ("&&", and, 1, -1, false);
      basic.Defun ("or", or, 1, -1, false);
      basic.Defun ("||", or, 1, -1, false);
      basic.Defun ("not", not, 1, 1, false);
      basic.Defun ("!", not, 1, 1, false);
      basic.Defun ("add", add, 2, -1, false);
      basic.Defun ("+", add, 2, -1, false);
      basic.Defun ("mul", mul, 2, -1, false);
      basic.Defun ("*", mul, 2, -1, false);
      basic.Defun ("sub", sub, 1, -1, false);
      basic.Defun ("-", sub, 1, -1, false);
      basic.Defun ("div", div, 2, -1, false);
      basic.Defun ("/", div, 2, -1, false);
      basic.Defun ("mod", mod, 2, 2, false);
      basic.Defun ("%", mod, 2, 2, false);
      basic.Defun ("logior", logior, 2, -1, false);
      basic.Defun ("|", logior, 2, -1, false);
      basic.Defun ("logand", logand, 2, -1, false);
      basic.Defun ("&", logand, 2, -1, false);
      basic.Defun ("add-set", add_set, 2, -1, true);
      basic.Defun ("+=", add_set, 2, -1, true);
      basic.Defun ("mul-set", mul_set, 2, -1, true);
      basic.Defun ("*=", mul_set, 2, -1, true);
      basic.Defun ("sub-set", sub_set, 2, -1, true);
      basic.Defun ("-=", sub_set, 2, -1, true);
      basic.Defun ("div-set", div_set, 2, -1, true);
      basic.Defun ("/=", div_set, 2, -1, true);
      basic.Defun ("mod-set", mod_set, 2, 2, true);
      basic.Defun ("%=", mod_set, 2, 2, true);
      basic.Defun ("logior-set", logior_set, 2, -1, true);
      basic.Defun ("|=", logior_set, 2, -1, true);
      basic.Defun ("logand-set", logand_set, 2, -1, true);
      basic.Defun ("&=", logand_set, 2, -1, true);
      basic.Defun ("lsh", lsh, 2, 2, false);
      basic.Defun ("<<", lsh, 2, 2, false);
      basic.Defun ("rsh", rsh, 2, 2, false);
      basic.Defun (">>", rsh, 2, 2, false);
      basic.Defun ("lsh-set", lsh_set, 2, 2, true);
      basic.Defun ("<<=", lsh_set, 2, 2, true);
      basic.Defun ("rsh-set", rsh_set, 2, 2, true);
      basic.Defun (">>=", rsh_set, 2, 2, true);
      basic.Defun ("eq", eq, 2, -1, false);
      basic.Defun ("==", eq, 2, -1, false);
      basic.Defun ("noteq", noteq, 2, 2, false);
      basic.Defun ("!=", noteq, 2, 2, false);
      basic.Defun ("lt", less_than, 2, -1, false);
      basic.Defun ("<", less_than, 2, -1, false);
      basic.Defun ("le", less_eq, 2, -1, false);
      basic.Defun ("<=", less_eq, 2, -1, false);
      basic.Defun ("gt", greater_than, 2, -1, false);
      basic.Defun (">", greater_than, 2, -1, false);
      basic.Defun ("ge", greater_eq, 2, -1, false);
      basic.Defun (">=", greater_eq, 2, -1, false);
      basic.Defun ("eval", eval_clause, 1, 1, true);
      basic.Defun ("progn", progn_clause, 0, -1, true);
      basic.Defun ("expr", progn_clause, 0, -1, true);
      basic.Defun ("if", if_clause, 2, -1, true);
      basic.Defun ("when", when_clause, 1, -1, true);
      basic.Defun ("while", while_clause, 1, -1, true);

      Fprogn = basic.GetFunc (Nprogn);
    }

    private static bool is_true (object val)
    {
      return (val is bool ? (bool) val
	      : val is int ? (int) val == 0
	      : true);
    }

    private static object set_value (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);

      vari.Value = args[1].val;
      return vari.val;
    }

    private static object and (Xex[] args, Domain domain)
    {
      foreach (Xex arg in args)
	if (! is_true (arg.val))
	  return false;
      return true;
    }

    private static object or (Xex[] args, Domain domain)
    {
      foreach (Xex arg in args)
	if (is_true (arg.val))
	  return true;
      return false;
    }

    private static object not (Xex[] args, Domain domain)
    {
      return ! is_true (args[0].val);
    }

    private static object add (Xex[] args, Domain domain)
    {
      int n = 0;
      foreach (Xex e in args)
	n += (int) e.val;
      return n;
    }

    private static object mul (Xex[] args, Domain domain)
    {
      int n = 1;
      foreach (Xex e in args)
	n *= (int) e.val;
      return n;
    }

    private static object sub (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;
      if (args.Length == 1)
	return - n;
      for (int i = 1; i < args.Length; i++)
	n -= (int) args[i].val;
      return n;
    }

    private static object div (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;
      for (int i = 1; i < args.Length; i++)
	n /= (int) args[i].val;
      return n;
    }

    private static object mod (Xex[] args, Domain domain)
    {
      return ((int) args[0].val % (int) args[1].val);
    }

    private static object logior (Xex[] args, Domain domain)
    {
      int n = 0;
      foreach (Xex e in args)
	n |= (int) e.val;
      return n;
    }

    private static object logand (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;
      for (int i = 1; i < args.Length; i++)
	n &= (int) args[i].val;
      return n;
    }

    private static object add_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      for (int i = 1; i < args.Length; i++)
	n += (int) args[i].val;
      vari.val = n;
      return n;
    }

    private static object mul_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      for (int i = 1; i < args.Length; i++)
	n *= (int) args[i].val;
      vari.val = n;
      return n;
    }

    private static object sub_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      for (int i = 1; i < args.Length; i++)
	n -= (int) args[i].val;
      vari.val = n;
      return n;
    }

    private static object div_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      for (int i = 1; i < args.Length; i++)
	n /= (int) args[i].val;
      vari.val = n;
      return n;
    }

    private static object mod_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      for (int i = 1; i < args.Length; i++)
	n %= (int) args[i].val;
      vari.val = n;
      return n;
    }

    private static object logior_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      for (int i = 1; i < args.Length; i++)
	n |= (int) args[i].val;
      vari.val = n;
      return n;
    }

    private static object logand_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      for (int i = 1; i < args.Length; i++)
	n &= (int) args[i].val;
      vari.val = n;
      return n;
    }

    private static object lsh (Xex[] args, Domain domain)
    {
      return (int) args[0].val << (int) args[1].val;
    }

    private static object lsh_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      n <<= (int) args[1].val;
      vari.val = n;
      return n;
    }

    private static object rsh (Xex[] args, Domain domain)
    {
      return (int) args[0].val >> (int) args[1].val;
    }

    private static object rsh_set (Xex[] args, Domain domain)
    {
      Variable vari = domain.GetVar (args[0]);
      int n = (int) vari.val;

      n >>= (int) args[1].val;
      vari.val = n;
      return n;
    }

    private static object eq (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;

      for (int i = 1; i < args.Length; i++)
	if (n != (int) args[i].val)
	  return false;
      return true;
    }

    private static object noteq (Xex[] args, Domain domain)
    {
      return ((int) args[0].val != (int) args[1].val);
    }

    private static object less_than (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;

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

    private static object less_eq (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;
      for (int i = 1; i < args.Length; i++)
	{
	  int n1 = (int) args[i].val;
	  if (n > n1)
	    return false;
	  n = n1;
	}
      return true;
    }

    private static object greater_than (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;
      for (int i = 1; i < args.Length; i++)
	{
	  int n1 = (int) args[i].val;
	  if (n <= n1)
	    return false;
	  n = n1;
	}
      return true;
    }

    private static object greater_eq (Xex[] args, Domain domain)
    {
      int n = (int) args[0].val;
      for (int i = 1; i < args.Length; i++)
	{
	  int n1 = (int) args[i].val;
	  if (n < n1)
	    return false;
	  n = n1;
	}
      return true;
    }

    private static object eval_clause (Xex[] args, Domain domain)
    {
      return args[0].Eval (domain);
    }

    private static object progn_clause (Xex[] args, Domain domain)
    {
      object result = true;

      foreach (Xex e in args)
	result = e.Eval (domain);
      return result;
    }

    private static object if_clause (Xex[] args, Domain domain)
    {
      object result;

      if (is_true (args[0].Eval (domain)))
	result = args[1].Eval (domain);
      else
	{
	  result = false;
	  for (int i = 2; i < args.Length; i++)
	    result = args[i].Eval (domain);
	}
      return result;
    }

    private static object when_clause (Xex[] args, Domain domain)
    {
      if (! is_true (args[0].Eval (domain)))
	return false;

      object result = true;
      for (int i = 1; i < args.Length; i++)
	result = args[i].Eval (domain);
      return result;
    }

    private static object while_clause (Xex[] args, Domain domain)
    {
      while (is_true (args[0].Eval (domain)))
	for (int i = 1; i < args.Length; i++)
	  args[i].Eval (domain);
      return false;
    }

    // FUNCALL: function != null
    // VARREF:  function == null, args[0] = DIRECT-SYMBOL
    // DIRECT:  function == null, args == null

    private Function function;
    private Xex[] args;
    private object val;

    public Xex[] Args { get { return args; } }
    public object Val { get { return val; } }

    private Xex () { }

    private Xex (object val)
    {
      this.val = val;
    }

    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 int pre_parse (XmlNodeList nlist, Domain domain)
    {
      int len = 0;
      foreach (XmlNode node in nlist)
	{
	  if (node.Name == Ndefun)
	    domain.RegisterFunction (node);
	  else if (node.Name == Ndefvar)
	    domain.Defvar ((Name) node.Attributes[0].Value, node.FirstChild);
	  else
	    len++;
	}
      return len;
    }

    private void post_parse (XmlNodeList nlist, Domain domain)
    {
      for (int i = 0, j = 0; i < nlist.Count; i++)
	{
	  XmlNode node = nlist[i];

	  if (node.Name == Ndefun)
	    domain.Defun (node);
	  else if (node.Name != Ndefvar)
	    args[j++] = new Xex (node, domain);
	}
    }

    private void Setup (XmlNode node, Domain domain)
    {
      Name name = node.Name;

      if (name == Nconst)
	{
	  Name type = node.Attributes[Ntype].Value;

	  if (type == Ninteger)
	    val = parse_integer (node.InnerText);
	  else if (type == Nstring)
	    val = node.InnerText;
	  else if (type == Nsymbol)
	    val = (Name) node.InnerText;
	  else if (type == Nboolean)
	    val = node.InnerText == "true";
	  else if (type == Nlist)
	    {
	      List<Xex> list = new List<Xex> ();
	      for (XmlNode n = node.FirstChild; n != null; n = n.NextSibling)
		list.Add (new Xex (n, domain));
	      val = list;
	    }
	  else
	    throw new Exception ("Unknown type: " + type);
	}
      else if (name == Nvariable)
	{
	  args = new Xex[1];
	  args[0] = new Xex ((Name) node.Attributes[0].Value);
	}
      else
	{
	  if (name == Nfuncall)
	    name = node.Attributes[0].Value;
	  function = domain.GetFunc (name);

	  XmlNodeList nlist = node.ChildNodes;
	  int nargs = nlist.Count;

	  if (nargs < function.min_arg
	      || (function.max_arg >= 0 && nargs > function.max_arg))
	    throw new Exception ("Invalid number of arguments to: "
				 + name + " " + nargs);
	  nargs =  pre_parse (nlist, domain);
	  args = new Xex[nargs];
	  post_parse (nlist, domain);
	}
    }

    public Xex (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
		       || Nexpr != reader.Name));
	  if (reader.NodeType == XmlNodeType.None)
	    throw new Exception ("Node <expr> not found");
	  node = doc.ReadNode (reader);
	}

      Setup (node, domain);
    }

    // EXPR = SYMBOL | MTEXT | INTEGER | FUNCALL | PROGN
    // FUNCALL = '(' SYMBOL EXPR* ')'
    // PROGN = '(' EXPR * ')'
    public Xex (XmlNode node, Domain domain)
    {
      Setup (node, domain);
    }

    public object Eval (Domain domain)
    {
      if (function == null)
	{
	  if (args != null)
	    {
	      Variable vari = domain.GetVar ((Name) args[0].val);
	      val = vari.val;
	    }
	  return val;
	}
      else
	val = function.Call (args, domain);
      return val;
    }

    public override string ToString ()
    {
      string str;

      if (function != null)
	{
	  str = "(" + function.name;
	  if (args != null)
	    foreach (Xex e in args)
	      str += " " + e.ToString ();
	  str += ")";
	}
      else if (args != null)
	{
	  str = (Name) args[0].val;
	}
      else if (val != null)
	{
	  if (val is string)
	    str = "\"" + ((string) val) + "\"";
	  else
	    str = val.ToString ();
	}
      else
	str = "()";
      return str;
    }
  }
}