X-Git-Url: http://git.chise.org/gitweb/?a=blobdiff_plain;f=XmlExpr.cs;h=53c764182e5d58486a937efc58929d09175e92fb;hb=30c120fd525ae9e62a5ff580f23f3c5594379f45;hp=2e143a21293a4b8bf0430f10333150c66a791a8c;hpb=0f44ed40ba80ef72d6a8a835f4b980d6e3db4e50;p=m17n%2Fm17n-lib-cs.git

diff --git a/XmlExpr.cs b/XmlExpr.cs
index 2e143a2..53c7641 100644
--- a/XmlExpr.cs
+++ b/XmlExpr.cs
@@ -2,34 +2,34 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.IO;
+using System.Reflection;
 using System.Xml;
 
-namespace System.Xml.Expression
+namespace System.Xml
 {
   public class Xexpression
   {
-    public static int debug_level = 0;
+    private static int trace_depth = 0;
+
+    public static int TraceDepth {
+      get { return trace_depth; }
+      set { trace_depth = value; }
+    }
 
     public struct Symbol : IEquatable<Symbol>
     {
       private static NameTable nt = new NameTable ();
 
-      internal string name;
+      private string name;
 
-      public Symbol (string str)
-	{
-	  name = nt.Add (str);
-	}
+      public Symbol (string str) { name = nt.Add (str); }
 
       public static implicit operator Symbol (string str)
       {
 	return new Symbol (str);
       }
 
-      public static implicit operator string (Symbol name)
-      {
-	return name.name;
-      }
+      public static implicit operator string (Symbol sym) { return sym.name; }
 
       public static bool operator== (Symbol n1, Symbol n2)
 	{
@@ -68,7 +68,9 @@ namespace System.Xml.Expression
 
       public override bool Equals (object obj)
       {
-	return Object.ReferenceEquals (this.name, obj);
+	return (obj is Symbol ? this == (Symbol) obj
+		: obj is string ? this.name == (string) obj
+		: false);
       }
 
       public override int GetHashCode ()
@@ -76,7 +78,7 @@ namespace System.Xml.Expression
 	return name.GetHashCode ();
       }
 
-      public static NameTable Table { get { return nt; } }
+      public static NameTable NameTable { get { return nt; } }
 
       public override string ToString () { return name; }
     }
@@ -85,37 +87,60 @@ namespace System.Xml.Expression
 
     private static Symbol Qnull = "";
     private static Symbol Qfuncall = "funcall";
-    private static Symbol Qvarref = "varref";
     private static Symbol Qinteger = "integer";
     private static Symbol Qstring = "string";
     private static Symbol Qsymbol = "symbol";
     private static Symbol Qlist = "list";
 
-    private static Symbol Qdefun = "defun";
+    public static Symbol Qdefun = "defun";
+    public static Symbol Qdefmacro = "defmacro";
     private static Symbol Qfname = "fname";
     private static Symbol Qargs = "args";
-    private static Symbol Qargs_unevalled = "args-unevalled";
     private static Symbol Qfixed = "fixed";
     private static Symbol Qoptional = "optional";
     private static Symbol Qrest = "rest";
 
-    private static Symbol Qdefvar = "defvar";
+    public static Symbol Qdefvar = "defvar";
     private static Symbol Qvname = "vname";
     private static Symbol Qdescription = "description";
     private static Symbol Qrange = "range";
 
+    private static Symbol Qename = "ename";
+
+    public static partial class Error
+    {
+      // Load time errors.
+      public static Symbol UnknownFunction = "unknown function";
+      public static Symbol InvalidArgumentNumber = "invalid argument number";
+      public static Symbol VariableNotAcceptable = "variable not acceptable";
+    }
+
+    public static partial class Error
+    {
+      // Run time errors.
+      public static Symbol ArithmeticError = "arithmetic error";
+      public static Symbol InvalidArgumentType = "invalid argument type";
+      public static Symbol NoVariable = "no-variable";
+      public static Symbol InvalidVariableType = "invalid variable type";
+      public static Symbol NoOuterLoop = "no outer loop";
+      public static Symbol UnknownError = "unknown error";
+    }
+
+
     public abstract class Function
     {
       public Symbol name;
       public int min_arg, max_arg;
+      public bool setvar;
 
       public Function () { }
 
-      public Function (Symbol name, int min_arg, int max_arg)
+      public Function (Symbol name, int min_arg, int max_arg, bool setvar)
       {
 	this.name = name;
 	this.min_arg = min_arg;
 	this.max_arg = max_arg;
+	this.setvar = setvar;
       }
 
       public abstract Term Call (Domain domain, Variable vari, Term[] args);
@@ -128,25 +153,23 @@ namespace System.Xml.Expression
       internal class Subroutine : Function
       {
 	public Builtin builtin;
-	public bool setvar;
 
 	public Subroutine (Builtin builtin, Symbol name, bool setvar,
 			   int min_arg, int max_arg)
-	  : base (name, min_arg, max_arg)
+	  : base (name, min_arg, max_arg, setvar)
 	  {
 	    this.builtin = builtin;
-	    this.setvar = setvar;
 	  }
 
 	public override Term Call (Domain domain, Variable vari, Term[] args)
 	{
-	  if (args != null)
+	  if (args.Length > 0)
 	    {
 	      args = (Term[]) args.Clone ();
 	      for (int i = 0; i < args.Length; i++)
 		{
 		  args[i] = args[i].Eval (domain);
-		  if (domain.Thrown)
+		  if (domain.Thrown ())
 		    return args[i];
 		}
 	    }
@@ -158,9 +181,9 @@ namespace System.Xml.Expression
       {
 	public Builtin builtin;
 
-	public SpecialForm (Builtin builtin, Symbol name,
+	public SpecialForm (Builtin builtin, Symbol name, bool setvar,
 			    int min_arg, int max_arg)
-	  : base (name, min_arg, max_arg)
+	  : base (name, min_arg, max_arg, setvar)
 	  {
 	    this.builtin = builtin;
 	  }
@@ -171,61 +194,140 @@ namespace System.Xml.Expression
 	}
       }
 
+      private static void parse_head (Domain domain, XmlNode node,
+				      out Symbol name,
+				      out int min_arg, out int max_arg,
+				      out Variable[] args)
+      {
+	int nfixed = 0;
+	int noptional = 0;
+	int nrest = 0;
+	name = node.Attributes[Qfname].Value;
+	    
+	node = node.FirstChild;
+	if (node != null && node.Name == Qargs)
+	  {
+	    XmlNode n;
+	    for (n = node.FirstChild; n != null; n = n.NextSibling)
+	      {
+		if (n.Name == Qfixed)
+		  nfixed += n.ChildNodes.Count;
+		else if (n.Name == Qoptional)
+		  noptional += n.ChildNodes.Count;
+		else if (n.Name == Qrest)
+		  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)
+	      {
+		for (XmlNode nn = n.FirstChild; nn != null; nn = nn.NextSibling)
+		  args[i++] = domain.Defvar ((Symbol) nn.Attributes[0].Value);
+	      }
+	    if (nrest == 1)
+	      max_arg = - max_arg;
+	  }
+	else
+	  {
+	    min_arg = max_arg = 0;
+	    args = new Variable[0];
+	  }
+      }
+
+      private static void parse_body (Domain domain, XmlNode node,
+				      out Term[] body)
+      {
+	for (node = node.FirstChild; node != null; node = node.NextSibling)
+	  if (node.Name != Qdescription
+	      && node.Name != Qargs)
+	    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 (domain, node);
+	  }
+	else
+	  body = null;
+      }
+
+      internal class Macro : Function
+      {
+	internal Variable[] args;
+	internal Term[] body;
+
+	public Macro (Domain domain, XmlNode node)
+	  {
+	    parse_head (domain, node, out name, out min_arg, out max_arg,
+			out args);
+	    setvar = false;
+	  }
+
+	public void SetBody (Domain domain, XmlNode node)
+	{
+	  parse_body (domain, node, out body);
+	}
+
+	public override Term Call (Domain domain, Variable vari, Term[] args)
+	{
+	  Bindings current = domain.bindings;
+	  Term result = Zero;
+	  int rest_idx = max_idx < 0 ? - max_idx : args.Length;
+
+	  for (int i = 0; i < rest_idx; i++)
+	    domain.Bind (this.args[i], args[i]);
+	  if (i < args.Length)
+	    {
+	      List<Term> rest = new List<Term> ();
+
+	      for (; i < args.Length; i++)
+		rest.Add (args[i]);
+	      domain.Bind (this.args[rest_idx], rest);
+	    }
+
+	  if (body != null)
+	    {
+	      domain.Catch (CatchTag.Return);
+	      foreach (Term term in body)
+		{
+		  result = term.Eval (domain);
+		  if (domain.Thrown ())
+		    break;
+		}
+	      domain.Uncatch ();
+	    }
+	  domain.UnboundTo (current);
+	  return result;
+	}
+      }
+
       internal class Lambda : Function
       {
-	internal bool args_evalled;
 	internal Variable[] args;
 	internal Term[] body;
 
 	public Lambda (Domain domain, XmlNode node)
 	  {
-	    int nfixed = 0;
-	    int noptional = 0;
-	    int nrest = 0;
-	    name = node.Attributes[Qfname].Value;
-	    
-	    node = node.FirstChild;
-	    if (node != null
-		&& (node.Name == Qargs || node.Name == Qargs_unevalled))
-	      {
-		XmlNode n;
-		args_evalled = node.Name == Qargs;
-		for (n = node.FirstChild; n != null; n = n.NextSibling)
-		  {
-		    if (n.Name == Qfixed)
-		      nfixed++;
-		    else if (n.Name == Qoptional)
-		      noptional++;
-		    else if (n.Name == Qrest)
-		      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 ((Symbol) n.Attributes[0].Value);
-		if (nrest == 1)
-		  max_arg = - max_arg;
-	      }
-	    else
-	      {
-		min_arg = max_arg = 0;
-	      }
+	    parse_head (domain, node, out name, out min_arg, out max_arg,
+			out args);
+	    setvar = false;
 	  }
 
-	public Lambda (Domain domain, Symbol name,
-		       bool args_evalled, Symbol[] args)
+	public Lambda (Domain domain, Symbol name, Symbol[] args)
 	  {
 	    int nfixed = 0;
 	    int noptional = 0;
 	    int nrest = 0;
 
 	    this.name = name;
-	    this.args_evalled = args_evalled;
-	    if (args != null)
+	    if (args.Length > 0)
 	      {
 		int i = 0;
 		for (i = 0; i < args.Length; i++, nfixed++)
@@ -254,24 +356,12 @@ namespace System.Xml.Expression
 	      {
 		min_arg = max_arg = 0;
 	      }
+	    setvar = false;
 	  }
 
 	public void SetBody (Domain domain, XmlNode node)
 	{
-	  for (node = node.FirstChild; node != null; node = node.NextSibling)
-	    if (node.Name != Qdescription
-		&& node.Name != Qargs
-		&& node.Name != Qargs_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 (domain, node);
-	    }
+	  parse_body (domain, node, out body);
 	}
 
 	public void SetBody (Term[] body)
@@ -286,7 +376,7 @@ namespace System.Xml.Expression
 
 	  try {
 	    int i;
-	    if (args_evalled)
+	    if (args.Length > 0)
 	      {
 		Term[] newargs = new Term[args.Length];
 		for (i = 0; i < min_arg; i++)
@@ -298,17 +388,15 @@ namespace System.Xml.Expression
 	    if (body != null)
 	      {
 		try {
-		  if (args_evalled)
-		    domain.Catch (CatchTag.Return);
+		  domain.Catch (CatchTag.Return);
 		  foreach (Term term in body)
 		    {
 		      result = term.Eval (domain);
-		      if (domain.Thrown)
+		      if (domain.Thrown ())
 			return result;
 		    }
 		} finally {
-		  if (args_evalled)
-		    domain.Uncatch ();
+		  domain.Uncatch ();
 		}
 	      }
 	  } finally {
@@ -319,32 +407,28 @@ namespace System.Xml.Expression
       }
     }
 
-    public class Variable : TermValue
+    public class Variable
     {
+      public Domain domain;
       public readonly Symbol name;
-      public string desc;
-      internal Term default_val;
-      internal Term val;
-      object range;
+      protected Term val;
 
-      public Variable (Symbol name, Term value)
+      public Variable (Domain domain, Symbol name, Term val)
       {
+	this.domain = domain;
 	this.name = name;
-	val = value;
-	default_val = Zero;
+	this.val = val;
       }
 
       public virtual bool ValueP (Term val) { return true; }
 
-      public override TermValue Clone ()
+      public virtual Variable Clone (Domain domain)
       {
-	Variable v = new Variable (name, val);
-	v.desc = desc;
-	v.default_val = default_val;
-	v.range = range;
-	return v;
+	return new Variable (domain, name, val);
       }
 
+      public virtual void Reset () { val = Zero; }
+
       public Term Value
       {
 	get { return val; }
@@ -355,192 +439,190 @@ namespace System.Xml.Expression
 	}
       }
 
-      public Term DefaultValue
+      public Term SetValue (int i)
       {
-	get { return default_val; }
-	set {
-	  if (! ValueP (value))
-	    throw new Exception ("Invalid value: " + value);
-	  default_val = value;
-	}
+	val.intval = i;
+	val.objval = null;
+	return val;
       }
 
-      public virtual object Range
+      public Term SetValue (string s)
       {
-	get { return range; }
-	set { range = value; }
+	val.objval = s;
+	return val;
       }
 
-      public override Term Eval (Domain domain) { return val; }
-
       public override string ToString () { return name + "(" + val + ")"; }
 
-      public class Int : Variable
+      public abstract class Typed : Variable
+      {
+	protected string desc;
+	private Term default_val;
+
+	protected Typed (Domain domain, Symbol name, Term val, string desc)
+	  : base (domain, name, val)
+	  {
+	    this.desc = desc;
+	    default_val = val;
+	  }
+
+	public override void Reset () { val = default_val; }
+
+	public string Description {
+	  get { return desc; }
+	  set { desc = value; }
+	}
+      }
+
+      public class Int : Typed
       {
-	public int[] range;
+	private int[] range;
 
-	private static bool SubsetP (int[] r1, int[] r2)
+	public bool IsSubrange (int[] r)
 	  {
-	    if (r2 == null)
+	    if (range == null)
 	      return true;
-	    for (int i = 0; i < r1.Length; i += 2)
+	    for (int i = 0; i < r.Length; i += 2)
 	      {
 		int j;
-		for (j = 0; j < r2.Length; j += 2)
-		  if (r2[j] <= r1[i] && r2[j + 1] >= r1[i + 1])
+		for (j = 0; j < range.Length; j += 2)
+		  if (range[j] <= r[i] && range[j + 1] >= r[i + 1])
 		    break;
-		if (j >= r2.Length)
+		if (j >= range.Length)
 		  return false;
 	      }
 	    return true;
 	  }
 
-	private static bool SubsetP (int val, int[] r)
+	public Int (Domain domain, Symbol name, int n, string desc, int[] range)
+	  : base (domain, name, new Term (n), desc)
 	  {
-	    if (r == null)
-	      return true;
-	    for (int i = 0; i < r.Length; i += 2)
-	      if (r[i] <= val && r[i + 1] >= val)
-		return true;
-	    return false;
-	  }
-
-	public Int (Symbol name, string description, int value, int[] range)
-	  : base (name, new Term (value))
-	  {
-	    if (! SubsetP (value, range))
-	      throw new Exception ("Invalid value: " + value);
-	    desc = description;
-	    default_val = val;
+	    if (range != null && range.Length % 2 == 1)
+	      throw_exception ("Range length for {0} not even", name);
 	    this.range = range;
+	    if (! ValueP (val))
+	      throw_exception ("Invalid integer value for {0}: {1}", name, val);
 	  }
 
 	public override bool ValueP (Term term)
 	{
 	  if (! term.IsInt)
 	    return false;
-	  return SubsetP (term.Intval, range);
+	  if (range == null)
+	    return true;
+	  int n = term.Intval;
+	  for (int i = 0; i < range.Length; i += 2)
+	    if (range[i] <= n && range[i + 1] >= n)
+	      return true;
+	  return false;
 	}
 
-	public override object Range {
-	  get { return range; }
-	  set {
-	    int[] r = (int[]) value;
-	    if (! SubsetP (r, range)
-		|| ! SubsetP (val.Intval, r)
-		|| ! SubsetP (default_val.Intval, r))
-	      throw new Exception ("Invalid range");
-	    range = r;
-	  }
+	public override Variable Clone (Domain domain)
+	{
+	  return new Int (domain, name, val.Intval, desc, range);
 	}
+
+	public int[] Range { get { return range; } set { range = value; } }
       }
 
-      public class Str : Variable
+      public class Str : Typed
       {
-	public string[] range;
+	private string[] range;
 
-	private static bool SubsetP (string[] r1, string[] r2)
+	public bool IsSubrange (string[] r)
 	  {
-	    if (r2 == null)
+	    if (range == null)
 	      return true;
-	    foreach (string s in r1)
-	      if (! SubsetP (s, r2))
-		return false;
+	    for (int i = 0; i < r.Length; i++)
+	      {
+		int j;
+		for (j = 0; j < range.Length; j++)
+		  if (range[j] == r[i])
+		    break;
+		if (j >= range.Length)
+		  return false;
+	      }
 	    return true;
 	  }
 
-	private static bool SubsetP (string str, string[] r)
+	public Str (Domain domain, Symbol name, string str, string desc,
+		    string[] range)
+	  : base (domain, name, new Term (str), desc)
 	  {
-	    if (r == null)
-	      return true;
-	    foreach (string s in r)
-	      if (str == s)
-		return true;
-	    return false;
-	}
-
-	public Str (Symbol name, string description, string value, string[] range)
-	  : base (name, new Term (value))
-	  {
-	    if (! SubsetP (value, range))
-	      throw new Exception ("Invalid value: " + value);
-	    desc = description;
-	    default_val = val;
 	    this.range = range;
+	    if (! ValueP (val))
+	      throw_exception ("Invalid string value for {0}: {1}", name, val);
 	  }
 
 	public override bool ValueP (Term term)
 	{
-	  if (! (term.objval is string))
+	  if (! term.IsStr)
 	    return false;
-	  return SubsetP (term.Strval, range);
+	  if (range == null)
+	    return true;
+	  string str = term.Strval;
+	  foreach (string s in range)
+	    if (str == s)
+	      return true;
+	  return false;
 	}
 
-	public override object Range {
-	  get { return range; }
-	  set {
-	    string[] r = (string[]) value;
-	    if (! SubsetP (r, range)
-		|| ! SubsetP (val.Strval, r)
-		|| ! SubsetP (default_val.Strval, r))
-	      throw new Exception ("Invalid range");
-	    range = r;
-	  }
+	public override Variable Clone (Domain domain)
+	{
+	  return new Str (domain, name, val.Strval, desc, range);
 	}
+
+	public string[] Range { get { return range; } set { range = value; } }
       }
 
-      public class Sym : Variable
+      public class Sym : Typed
       {
 	public Symbol[] range;
 
-	private static bool SubsetP (Symbol[] r1, Symbol[] r2)
+	public bool IsSubrange (Symbol[] r)
 	  {
-	    if (r2 == null)
+	    if (range == null)
 	      return true;
-	    foreach (Symbol n in r1)
-	      if (! SubsetP (n, r2))
-		return false;
+	    for (int i = 0; i < r.Length; i++)
+	      {
+		int j;
+		for (j = 0; j < range.Length; j++)
+		  if (range[j] == r[i])
+		    break;
+		if (j >= range.Length)
+		  return false;
+	      }
 	    return true;
 	  }
 
-	private static bool SubsetP (Symbol name, Symbol[] r)
+	public Sym (Domain domain, Symbol name, Symbol sym, string desc,
+		    Symbol[] range)
+	  : base (domain, name, new Term (sym), desc)
 	  {
-	    if (r == null)
-	      return true;
-	    foreach (Symbol n in r)
-	      if (name == n)
-		return true;
-	    return false;
-	}
-
-	public Sym (Symbol name, string description, Symbol value, Symbol[] range)
-	  : base (name, new Term (value))
-	  {
-	    if (! SubsetP (value, range))
-	      throw new Exception ("Invalid value: " + value);
-	    desc = description;
-	    default_val = val;
 	    this.range = range;
+	    if (! ValueP (val))
+	      throw_exception ("Invalid symbol value for {0}: {1}", name, val);
 	  }
 
 	public override bool ValueP (Term term)
 	{
-	  if (! (term.objval is Symbol))
+	  if (! term.IsSymbol)
 	    return false;
-	  return SubsetP (term.Symval, range);
+	  if (range == null)
+	    return true;
+	  Symbol name = term.Symval;
+	  foreach (Symbol n in range)
+	    if (name == n)
+	      return true;
+	  return false;
 	}
 
-	public override object Range {
-	  get { return range; }
-	  set {
-	    Symbol[] r = (Symbol[]) value;
-	    if (! SubsetP (r, range)
-		|| ! SubsetP (val.Symval, r)
-		|| ! SubsetP (default_val.Symval, r))
-	      throw new Exception ("Invalid range");
-	    range = r;
-	  }
+	public override Variable Clone (Domain domain)
+	{
+	  return new Sym (domain, name, val.Symval, desc, range);
 	}
+
+	public Symbol[] Range { get { return range; } set { range = value; } }
       }
     }
 
@@ -553,7 +635,7 @@ namespace System.Xml.Expression
       private Bindings (Variable vari)
       {
 	this.vari = vari;
-	old_value = vari.val;
+	old_value = vari.Value;
       }
 	
       public static Bindings Bind (Bindings bindings, Variable vari, Term val)
@@ -568,7 +650,7 @@ namespace System.Xml.Expression
       internal Bindings UnboundTo (Bindings boundary)
       {
 	for (Bindings b = this; b != boundary; b = b.next)
-	  b.vari.val = b.old_value;
+	  b.vari.Value = b.old_value;
 	return boundary;
       }
 
@@ -581,49 +663,35 @@ namespace System.Xml.Expression
       }
     }
 
-#if false
-    internal class ThrowException : Exception
+    private static void throw_exception (string fmt, params object[] args)
     {
-      Symbol tag;
-      public object value;
-
-      public ThrowException (Symbol tag, object value) : base ()
-	{
-	  this.tag = tag;
-	  this.value = value;
-	}
+      throw new Exception (String.Format (fmt, args));
     }
-#endif
 
-    internal class CatchTag : IEquatable<CatchTag>
+    internal struct CatchTag
     {
-      private object val;
+      private Term tag;
+
+      public CatchTag (Symbol sym) { tag = new Term (sym); }
+      public CatchTag (Symbol sym, string msg) { tag = new Term (sym, msg); }
+      public CatchTag (ErrorTerm e) { tag = new Term (e); }
+      private CatchTag (int i) { tag = new Term (i); }
 
-      public CatchTag (Symbol name) { val = name.name; }
-      private CatchTag (int i) { val = i; }
+      public Term Tag { get { return tag; } }
 
       public static CatchTag Return = new CatchTag (0);
       public static CatchTag Break = new CatchTag (1);
-
-      public static bool operator== (CatchTag t1, CatchTag t2)
-	{ return t1.val == t2.val; }
-
-      public static bool operator!= (CatchTag t1, CatchTag t2)
-	{ return t1.val != t2.val; }
-
-      public bool Equals (CatchTag tag) { return this.val == tag.val; }
-      public override bool Equals (object val) { return this.val == val; }
-
-      public override int GetHashCode () { return val.GetHashCode (); }
     }
 
     public class Domain
     {
+      public Symbol name;
       public object context;
       public int depth = 0;
+      private Stack<Term> call_stack = new Stack<Term> ();
 
-      internal Dictionary<Symbol, TermType> termtypes
-	= new Dictionary<Symbol, TermType> ();
+      internal Dictionary<Symbol, MethodInfo> termtypes
+	= new Dictionary<Symbol, MethodInfo> ();
       internal Dictionary<Symbol, Function> functions
 	= new Dictionary<Symbol, Function> ();
       internal Dictionary<Symbol, Variable> variables
@@ -632,18 +700,29 @@ namespace System.Xml.Expression
       private Stack<CatchTag> catch_stack = new Stack<CatchTag> ();
       private int catch_count = 0;
 
-      internal Domain () { }
+      internal Domain (Symbol name) { this.name = name; }
 
-      public Domain (object context) : this (basic, context) { }
+      public Domain (Symbol name, object context)
+        : this (name, basic, context) { }
 
-      public Domain (Domain parent, object context)
+      public Domain (Symbol name, Domain parent, object context) : this (name)
       {
-	termtypes = new Dictionary<Symbol, TermType> (parent.termtypes);
+	termtypes = new Dictionary<Symbol, MethodInfo> (parent.termtypes);
 	functions = new Dictionary<Symbol, Function> (parent.functions);
 	variables = new Dictionary<Symbol, Variable> (parent.variables);
 	this.context = context;
       }
 
+      internal void PushTerm (Term term)
+      {
+	call_stack.Push (term);
+      }
+
+      internal void PopTerm ()
+      {
+	call_stack.Pop ();
+      }
+
       internal void Bind (Variable vari, Term value)
       {
 	bindings = Bindings.Bind (bindings, vari, value);
@@ -668,46 +747,87 @@ namespace System.Xml.Expression
 	  catch_count--;
       }
 
-      public bool Thrown {
-	get { return catch_count < catch_stack.Count; }
+      public bool Thrown () { return catch_count < catch_stack.Count; }
+
+      public bool Thrown (out bool caught)
+      {
+	if (catch_count < catch_stack.Count)
+	  {
+	    caught = catch_count == catch_stack.Count - 1;
+	    return true;
+	  }
+	caught = false;
+	return false;
       }
 
       internal void ThrowReturn ()
       {
-	foreach (CatchTag tag in catch_stack)
+	foreach (CatchTag elt in catch_stack)
 	  {
 	    catch_count--;
-	    if (tag == CatchTag.Return)
+	    if (elt.Tag == CatchTag.Return.Tag)
 	      break;
 	  }
       }
 
-      internal void ThrowBreak ()
+      internal bool ThrowBreak ()
       {
-	if (catch_stack.Peek () != CatchTag.Break)
-	  throw new Exception ("No outer loop to break");
+	if (catch_stack.Peek ().Tag != CatchTag.Break.Tag)
+	  return false;
 	catch_count--;
+	return true;
+      }
+
+      internal void ThrowSymbol (Term tag)
+      {
+	foreach (CatchTag elt in catch_stack)
+	  {
+	    catch_count--;
+	    if (elt.Tag.Matches (tag))
+	      break;
+	  }
       }
 
-      internal void ThrowTag (CatchTag tag)
+      internal Term ThrowError (Term tag)
       {
+	tag = tag.Clone ();
+	ErrorTerm e = tag.objval as ErrorTerm;
+	e.CallStack = call_stack.ToArray ();
+
 	foreach (CatchTag elt in catch_stack)
 	  {
 	    catch_count--;
-	    if (elt == tag)
+	    if (elt.Tag.Matches (tag))
 	      break;
 	  }
+	return tag;
       }
 
-      public void DefTerm (Symbol name, TermParser parser)
+      public void DefType (Type type)
       {
-	termtypes[name] = new TermType (name, parser);
+	if (! type.IsSubclassOf (typeof (TermValue)))
+	  throw new Exception ("Not a subclass of TermValue: " + type);
+	BindingFlags flags = BindingFlags.Static | BindingFlags.NonPublic;
+	FieldInfo finfo = type.GetField ("name", flags);
+	if (finfo == null || finfo.FieldType != typeof (Symbol))
+	  throw new Exception ("No \"name\" field of string type: " + type);
+	Symbol name = (Symbol) finfo.GetValue (null);
+	if (termtypes.ContainsKey (name)
+	    || functions.ContainsKey (name))
+	  throw new Exception ("already defined: " + name);
+	Type[] types = new Type[] { typeof (Domain), typeof (XmlNode) };
+	MethodInfo minfo = type.GetMethod ("Parser", types);
+	if (minfo == null || minfo.ReturnType != typeof (TermValue))
+	  throw new Exception ("No \"Parser\" method of correct type: " + type);
+	termtypes[name] = minfo;
       }
 
       public void DefSubr (Builtin builtin, string str, bool setvar,
 			   int min_arg, int max_arg, params string[] aliases)
       {
 	Symbol name = str;
+	if (termtypes.ContainsKey (name))
+	  throw new Exception ("already defined as termtype: " + name);
 	Function func = new Function.Subroutine (builtin, name, setvar,
 						 min_arg, max_arg);
 	functions[name] = func;
@@ -715,12 +835,14 @@ namespace System.Xml.Expression
 	  functions[(Symbol) a] = func;
       }
 
-      public void DefSpecial (Builtin builtin, string str,
+      public void DefSpecial (Builtin builtin, string str, bool setvar,
 			      int min_arg, int max_arg,
 			      params string[] aliases)
       {
 	Symbol name = str;
-	Function func = new Function.SpecialForm (builtin, name,
+	if (termtypes.ContainsKey (name))
+	  throw new Exception ("already defined as termtype: " + name);
+	Function func = new Function.SpecialForm (builtin, name, setvar,
 						  min_arg, max_arg);
 	functions[name] = func;
 	foreach (string a in aliases)
@@ -732,14 +854,16 @@ namespace System.Xml.Expression
 	functions[(Symbol) alias] = functions[(Symbol) str];
       }
 
-      public void Defun (Symbol name, bool args_evalled,
-			 Symbol[] args, Term[] body, bool prototype)
+      public void Defun (Symbol name, Symbol[] args, Term[] body,
+			 bool prototype)
       {
 	Function func;
 
+	if (termtypes.ContainsKey (name))
+	  throw new Exception ("already defined as termtype: " + name);
 	if (prototype || ! functions.TryGetValue (name, out func))
 	  {
-	    func = new Function.Lambda (this, name, args_evalled, args);
+	    func = new Function.Lambda (this, name, args);
 	    functions[name] = func;
 	  }
 	if (! prototype)
@@ -749,6 +873,8 @@ namespace System.Xml.Expression
       public void Defun (XmlNode node, bool prototype)
       {
 	Symbol name = node.Attributes[Qfname].Value;
+	if (termtypes.ContainsKey (name))
+	  throw new Exception ("already defined as termtype: " + name);
 	Function func;
 
 	if (prototype || ! functions.TryGetValue (name, out func))
@@ -765,6 +891,22 @@ namespace System.Xml.Expression
 	functions[func.name] = func;
       }
 
+      public void Defmacro (XmlNode node, bool prototype)
+      {
+	Symbol name = node.Attributes[Qfname].Value;
+	if (termtypes.ContainsKey (name))
+	  throw new Exception ("already defined as termtype: " + name);
+	Function func;
+
+	if (prototype || ! functions.TryGetValue (name, out func))
+	  {
+	    func = new Function.Macro (this, node);
+	    functions[name] = func;
+	  }
+	if (! prototype)
+	  ((Function.Macro) func).SetBody (this, node);
+      }
+
       public Variable Defvar (XmlNode node)
       {
 	Symbol name = node.Attributes[0].Value;
@@ -795,43 +937,30 @@ namespace System.Xml.Expression
 
 	    if (type == Qinteger)
 	      {
-		int intval = parse_integer (val);
+		int n = parse_integer (val);
 		int[] range = null;
 		if (range_list != null)
 		  {
 		    range = new int[nranges * 2];
 		    for (int i = 0; i < nranges; i++)
 		      {
-			XmlNode n = range_list[i];
-			if (n.Name == Qrange)
+			XmlNode nd = range_list[i];
+			if (nd.Name == Qrange)
 			  {
 			    range[i * 2]
-			      = parse_integer (n.FirstChild.InnerText);
+			      = parse_integer (nd.FirstChild.InnerText);
 			    range[i * 2 + 1]
-			      = parse_integer (n.LastChild.InnerText);
+			      = parse_integer (nd.LastChild.InnerText);
 			  }
 			else
 			  {
 			    range[i * 2]
 			      = range[i * 2 + 1]
-			      = parse_integer (n.FirstChild.InnerText);
+			      = parse_integer (nd.FirstChild.InnerText);
 			  }
 		      }
 		  }
-
-		if (variables.TryGetValue (name, out vari))
-		  {
-		    if (! (vari is Variable.Int))
-		      throw new Exception ("Inalid value");
-		    vari = (Variable) vari.Clone ();
-		    Term v = new Term (intval);
-		    vari.Value = v;
-		    vari.DefaultValue = v;
-		    if (range != null)
-		      vari.Range = range;
-		  }
-		else
-		  vari = new Variable.Int (name, desc, intval, range);
+		vari = DefvarInt (name, n, desc, range);
 	      }
 	    else if (type == Qstring)
 	      {
@@ -842,20 +971,7 @@ namespace System.Xml.Expression
 		    for (int i = 0; i < nranges; i++)
 		      range[i] = range_list[i].FirstChild.InnerText;
 		  }
-
-		if (variables.TryGetValue (name, out vari))
-		  {
-		    if (! (vari is Variable.Str))
-		      throw new Exception ("Invalid value");
-		    vari = (Variable) vari.Clone ();
-		    Term v = new Term (val);
-		    vari.Value = v;
-		    vari.DefaultValue = v;
-		    if (range != null)
-		      vari.Range = range;
-		  }
-		else
-		  vari = new Variable.Str (name, desc, val, range);
+		vari = DefvarStr (name, val, desc, range);
 	      }
 	    else if (type == Qsymbol)
 	      {
@@ -866,20 +982,7 @@ namespace System.Xml.Expression
 		    for (int i = 0; i < nranges; i++)
 		      range[i] = range_list[i].FirstChild.InnerText;
 		  }
-
-		if (variables.TryGetValue (name, out vari))
-		  {
-		    if (! (vari is Variable.Sym))
-		      throw new Exception ("Invalid value");
-		    vari = (Variable) vari.Clone ();
-		    Term v = new Term (val);
-		    vari.Value = v;
-		    vari.DefaultValue = v;
-		    if (range != null)
-		      vari.Range = range;
-		  }
-		else
-		  vari = new Variable.Sym (name, desc, val, range);
+		vari = DefvarSym (name, (Symbol) val, desc, range);
 	      }
 	    else
 	      throw new Exception ("Unknown type: " + type);
@@ -887,27 +990,108 @@ namespace System.Xml.Expression
 	else
 	  {
 	    if (variables.TryGetValue (name, out vari))
-	      vari = (Variable) vari.Clone ();
+	      vari = vari.Clone (this);
 	    else
-	      vari = new Variable (name, Zero);
+	      vari = new Variable (this, name, Zero);
+	    variables[name] = vari;
 	  }
-	variables[name] = vari;
 	return vari;
       }
 
       public Variable Defvar (Variable vari)
       {
+	vari = vari.Clone (this);
 	variables[vari.name] = vari;
 	return vari;
       }
 
       internal Variable Defvar (Symbol name)
       {
-	Variable vari = new Variable (name, Zero);
+	Variable vari = new Variable (this, name, Zero);
 	variables[name] = vari;
 	return vari;
       }
 
+      public Variable DefvarInt (Symbol name, int n, string desc, int[] range)
+      {
+	Variable vari;
+
+	if (variables.TryGetValue (name, out vari))
+	  {
+	    Variable.Int intvari = vari as Variable.Int;
+	    if (intvari == null)
+	      throw new Exception ("Variable type mismatch: " + name);
+	    if (range != null)
+	      {
+		if (! intvari.IsSubrange (range))
+		  throw new Exception ("Variable range mismatch: " + name);
+		intvari.Range = range;;
+	      }
+	    if (desc != null)
+	      intvari.Description = desc;
+	  }
+	else
+	  {
+	    vari = new Variable.Int (this, name, n, desc, range);
+	    variables[name] = vari;
+	  }
+	return vari;
+      }
+
+      public Variable DefvarStr (Symbol name, string str, string desc,
+				 string[] range)
+      {
+	Variable vari;
+
+	if (variables.TryGetValue (name, out vari))
+	  {
+	    Variable.Str strvari = vari as Variable.Str;
+	    if (strvari == null)
+	      throw new Exception ("Variable type mismatch: " + name);
+	    if (range != null)
+	      {
+		if (! strvari.IsSubrange (range))
+		  throw new Exception ("Variable range mismatch: " + name);
+		strvari.Range = range;
+	      }
+	    if (desc != null)
+	      strvari.Description = desc;
+	  }
+	else
+	  {
+	    vari = new Variable.Str (this, name, str, desc, range);
+	    variables[name] = vari;
+	  }
+	return vari;
+      }
+
+      public Variable DefvarSym (Symbol name, Symbol sym, string desc,
+				 Symbol[] range)
+      {
+	Variable vari;
+
+	if (variables.TryGetValue (name, out vari))
+	  {
+	    Variable.Sym symvari = vari as Variable.Sym;
+	    if (symvari == null)
+	      throw new Exception ("Variable type mismatch: " + name);
+	    if (range != null)
+	      {
+		if (! symvari.IsSubrange (range))
+		  throw new Exception ("Variable range mismatch: " + name);
+		symvari.Range = range;
+	      }
+	    if (desc != null)
+	      symvari.Description = desc;
+	  }
+	else
+	  {
+	    vari = new Variable.Sym (this, name, sym, desc, range);
+	    variables[name] = vari;
+	  }
+	return vari;
+      }
+
       internal Function GetFunc (Symbol name)
       {
 	Function func;
@@ -939,7 +1123,7 @@ namespace System.Xml.Expression
 	  {
 	    if (! create)
 	      return null;
-	    variables[name] = vari = new Variable (name, Zero);
+	    variables[name] = vari = new Variable (this, name, Zero);
 	  }
 	return vari;
       }
@@ -951,7 +1135,7 @@ namespace System.Xml.Expression
 	  str += " " + kv.Key;
 	str += ") (variabls";
 	foreach (KeyValuePair<Symbol, Variable> kv in variables)
-	  str += " " + kv.Key;
+	  str += " " + kv.Value;
 	str += ")";
 	if (bindings != null)
 	  str += " " + bindings;
@@ -961,17 +1145,13 @@ namespace System.Xml.Expression
 	return str;
       }
 
-      internal void DebugWrite (bool head, string fmt, params string[] arg)
+      internal void TraceWrite (string fmt, params string[] arg)
       {
-	if (debug_level > depth)
+	if (trace_depth > depth)
 	  {
-	    if (head)
-	      {
-		Console.WriteLine ();
-		for (int i = 0; i < depth; i++)
-		  Console.Write (" ");
-	      }
-	    Console.Write (fmt, arg);
+	    for (int i = 0; i < depth; i++)
+	      Console.Write ("  ");
+	    Console.WriteLine (fmt, arg);
 	  }
       }
 
@@ -980,7 +1160,7 @@ namespace System.Xml.Expression
 	Dictionary<Variable,Term> values = new Dictionary<Variable,Term> ();
 
 	foreach (KeyValuePair<Symbol,Variable> kv in variables)
-	  values[kv.Value] = kv.Value.val.Clone ();
+	  values[kv.Value] = kv.Value.Value.Clone ();
 	return values;
       }
 
@@ -988,17 +1168,19 @@ namespace System.Xml.Expression
       {
 	foreach (KeyValuePair<Variable,Term> kv
 		 in (Dictionary<Variable,Term>) values)
-	  kv.Key.val = kv.Value;
+	  kv.Key.Value = kv.Value;
       }
     }
 
     public delegate Term Builtin (Domain domain, Variable vari, Term[] args);
 
-    private static Domain basic = new Domain ();
+    private static Domain basic = new Domain ("basic");
 
     static Xexpression ()
     {
-      basic.DefTerm ("funcall", Funcall.parser);
+      basic.DefType (typeof (Varref));
+      basic.DefType (typeof (Funcall));
+      basic.DefType (typeof (ErrorTerm));
 
       basic.DefSubr (Fset, "set", true, 1, 1, "=");
       basic.DefSubr (Fnot, "not", false, 1, 1, "!");
@@ -1026,26 +1208,28 @@ namespace System.Xml.Expression
       basic.DefSubr (Feval, "eval", false, 1, 1);
       basic.DefSubr (Fbreak, "break", false, 0, 1);
       basic.DefSubr (Freturn, "return", false, 0, 1);
-
-      basic.DefSpecial (Fand, "and", 1, -1, "&&");
-      basic.DefSpecial (For, "or", 1, -1, "||");
-      basic.DefSpecial (Fprogn, "progn", 0, -1, "expr");
-      basic.DefSpecial (Fif, "if", 2, 3);
-      basic.DefSpecial (Fwhen, "when", 1, -1);
-      basic.DefSpecial (Floop, "loop", 1, -1);
-      basic.DefSpecial (Fwhile, "while", 1, -1);
-      basic.DefSpecial (Fcond, "cond", 1, -1);
-      basic.DefSpecial (Fforeach, "foreach", 2, -1);
-      basic.DefSpecial (Fquote, "quote", 1, 1);
-      basic.DefSpecial (Ftype, "type", 1, 1);
-      basic.DefSpecial (Fcatch, "catch", 2, 2);
-      basic.DefSpecial (Fthrow, "throw", 1, 2);
+      basic.DefSubr (Fthrow, "throw", false, 1, 2);
+
+      basic.DefSpecial (Fand, "and", false, 1, -1, "&&");
+      basic.DefSpecial (For, "or", false, 1, -1, "||");
+      basic.DefSpecial (Fprogn, "progn", false, 0, -1, "expr");
+      basic.DefSpecial (Fif, "if", false, 2, 3);
+      basic.DefSpecial (Fwhen, "when", false, 1, -1);
+      basic.DefSpecial (Floop, "loop", false, 1, -1);
+      basic.DefSpecial (Fwhile, "while", false, 1, -1);
+      basic.DefSpecial (Fcond, "cond", false, 1, -1);
+      basic.DefSpecial (Fforeach, "foreach", true, 2, -1);
+      basic.DefSpecial (Fquote, "quote", false, 1, 1);
+      basic.DefSpecial (Ftype, "type", false, 1, 1);
+      basic.DefSpecial (Fcatch, "catch", true, 2, -1);
     }
 
     private static Term Fset (Domain domain, Variable vari, Term[] args)
     {
+      if (vari == null)
+	return new Term (new ErrorTerm (Error.NoVariable, ""));
       vari.Value = args[0];
-      return vari.val;
+      return args[0];
     }
 
     private static Term Fnot (Domain domain, Variable vari, Term[] args)
@@ -1055,25 +1239,19 @@ namespace System.Xml.Expression
 
     private static Term Fadd (Domain domain, Variable vari, Term[] args)
     {
-      int n = vari == null ? 0 : vari.val.Intval;
+      int n = vari == null ? 0 : vari.Value.Intval;
 
       foreach (Term arg in args)
 	n += arg.Intval;
-      if (vari == null)
-	return new Term (n);
-      vari.val.intval = n;
-      return vari.val;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Fmul (Domain domain, Variable vari, Term[] args)
     {
-      int n = vari == null ? 1 : vari.val.Intval;
+      int n = vari == null ? 1 : vari.Value.Intval;
       foreach (Term arg in args)
 	n *= arg.Intval;
-      if (vari == null)
-	return new Term (n);
-      vari.val.intval = n;
-      return vari.val;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Fsub (Domain domain, Variable vari, Term[] args)
@@ -1087,15 +1265,12 @@ namespace System.Xml.Expression
 	}
       else
 	{
-	  n = vari.val.Intval;
+	  n = vari.Value.Intval;
 	  i = 0;
 	}
       while (i < args.Length)
 	n -= args[i++].Intval;
-      if (vari == null)
-	return new Term (n);
-      vari.val.intval = n;
-      return vari.val;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Fdiv (Domain domain, Variable vari, Term[] args)
@@ -1109,34 +1284,27 @@ namespace System.Xml.Expression
 	}
       else
 	{
-	  n = vari.val.Intval;
+	  n = vari.Value.Intval;
 	  i = 0;
 	}
       while (i < args.Length)
 	n /= args[i++].Intval;
-      if (vari == null)
-	return new Term (n);
-      vari.val.intval = n;
-      return vari.val;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Fmod (Domain domain, Variable vari, Term[] args)
     {
-      if (vari == null)
-	return new Term (args[0].Intval % args[1].Intval);
-      vari.val.intval = vari.val.Intval % args[0].Intval;
-      return vari.val;
+      int n = args[0].Intval % args[1].Intval;
+
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Flogior (Domain domain, Variable vari, Term[] args)
     {
-      int n = vari == null ? 0 : vari.val.Intval;
+      int n = vari == null ? 0 : vari.Value.Intval;
       foreach (Term arg in args)
 	n |= arg.Intval;
-      if (vari == null)
-	return new Term (n);
-      vari.val.intval = n;
-      return vari.val;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Flogand (Domain domain, Variable vari, Term[] args)
@@ -1150,31 +1318,24 @@ namespace System.Xml.Expression
 	}
       else
 	{
-	  n = vari.val.Intval;
+	  n = vari.Value.Intval;
 	  i = 0;
 	}
       while (i < args.Length)
 	n &= args[i++].Intval;
-      if (vari == null)
-	return new Term (n);
-      vari.val.intval = n;
-      return vari.val;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Flsh (Domain domain, Variable vari, Term[] args)
     {
-      if (vari == null)
-	return new Term (args[0].Intval << args[1].Intval);
-      vari.val.intval = vari.val.Intval << args[0].Intval;
-      return vari.val;
+      int n = args[0].Intval << args[1].Intval;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Frsh (Domain domain, Variable vari, Term[] args)
     {
-      if (vari == null)
-	return new Term (args[0].Intval >> args[1].Intval);
-      vari.val.intval = vari.val.Intval >> args[0].Intval;
-      return vari.val;
+      int n = args[0].Intval >> args[1].Intval;
+      return (vari == null ? new Term (n) : vari.SetValue (n));
     }
 
     private static Term Feq (Domain domain, Variable vari, Term[] args)
@@ -1261,7 +1422,7 @@ namespace System.Xml.Expression
       if (vari == null)
 	list = new List<Term> ();
       else
-	list = vari.val.Listval;
+	list = vari.Value.Listval;
 
       foreach (Term arg in args)
 	{
@@ -1277,7 +1438,7 @@ namespace System.Xml.Expression
 	  result.objval = list;
 	  return result;
 	}
-      return vari.val;
+      return vari.Value;
     }
 
     private static Term Fconcat (Domain domain, Variable vari, Term[] args)
@@ -1287,7 +1448,7 @@ namespace System.Xml.Expression
       if (vari == null)
 	str = "";
       else
-	str = vari.val.Strval;
+	str = vari.Value.Strval;
 
       foreach (Term arg in args)
 	{
@@ -1299,15 +1460,15 @@ namespace System.Xml.Expression
 	  else
 	    str += (char) arg.Intval;
 	}
+
       if (vari == null)
 	{
-	  Term result;
-	  result.intval = 0;
-	  result.objval = str;
-	  return result;
+	  Term term;
+	  term.intval = 0;
+	  term.objval = str;
+	  return term;
 	}
-      vari.val.objval = str;
-      return vari.val;
+      return vari.SetValue (str);
     }
 
     private static Term Fnth (Domain domain, Variable vari, Term[] args)
@@ -1339,29 +1500,35 @@ namespace System.Xml.Expression
 
     private static Term Fins (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);
+      Term term = vari.Value;
+
+      if (term.IsStr)
+	{
+	  string str = term.Strval.Insert (args[0].Intval, args[1].Strval);
+	  vari.SetValue (str);
+	}
+      else if (vari.Value.IsList)
+	vari.Value.Listval.InsertRange (args[0].Intval, args[1].Listval);
       else
-	throw new Exception ("term is not collection: " + vari.val);
-      return vari.val;
+	throw new Exception ("term is not collection: " + vari.Value);
+      return vari.Value;
     }
 
     private static Term Fdel (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,
+      if (vari.Value.IsStr)
+	{
+	  string str
+	    = vari.Value.Strval.Remove (args[0].Intval,
+					args[1].Intval - args[0].Intval);
+	  vari.SetValue (str);
+	}
+      else if (vari.Value.IsList)
+	vari.Value.Listval.RemoveRange (args[0].Intval,
 				      args[1].Intval - args[0].Intval);
       else
-	throw new Exception ("term is not collection: " + vari.val);
-      return vari.val;
+	throw new Exception ("term is not collection: " + vari.Value);
+      return vari.Value;
     }
 
     private static Term Fand (Domain domain, Variable vari, Term[] args)
@@ -1421,7 +1588,8 @@ namespace System.Xml.Expression
 
     private static Term Fbreak (Domain domain, Variable vari, Term[] args)
     {
-      domain.ThrowBreak ();
+      if (! domain.ThrowBreak ())
+	return domain.ThrowError (new Term (Error.NoOuterLoop, null));
       return args.Length == 0 ? Zero : args[0];
     }	  
 
@@ -1430,11 +1598,11 @@ namespace System.Xml.Expression
       Term result = Zero;
       try {
 	domain.Catch (CatchTag.Break);
-	while (! domain.Thrown)
+	while (! domain.Thrown ())
 	  foreach (Term arg in args)
 	    {
 	      result = arg.Eval (domain);
-	      if (domain.Thrown)
+	      if (domain.Thrown ())
 		return result;
 	    }
       } finally {
@@ -1448,11 +1616,11 @@ namespace System.Xml.Expression
       Term result = Zero;
       try {
 	domain.Catch (CatchTag.Break);
-	while (! domain.Thrown && args[0].Eval (domain).IsTrue)
+	while (! domain.Thrown () && args[0].Eval (domain).IsTrue)
 	  for (int i = 1; i < args.Length; i++)
 	    {
 	      result = args[i].Eval (domain);
-	      if (domain.Thrown)
+	      if (domain.Thrown ())
 		return result;
 	    }
       } finally {
@@ -1471,18 +1639,23 @@ namespace System.Xml.Expression
 	  if (result.IsTrue)
 	    {
 	      for (int i = 1; i < list.Count; i++)
-		result = list[i].Eval (domain);
+		{
+		  domain.depth++;
+		  result = list[i].Eval (domain);
+		  domain.depth--;
+		  if (domain.Thrown ())
+		    return result;
+		}		  
 	      return result;
 	    }
 	}
       return Zero;
     }
 
-    private static Term Fforeach (Domain domain, Variable vari,
-					Term[] args)
+    private static Term Fforeach (Domain domain, Variable vari, Term[] args)
     {
       Term result = args[0].Eval (domain);
-      if (domain.Thrown)
+      if (domain.Thrown ())
 	return result;
       List<Term> list = result.Listval;
       Bindings current = domain.bindings;
@@ -1496,7 +1669,7 @@ namespace System.Xml.Expression
 	      for (int i = 1; i < args.Length; i++)
 		{
 		  result = args[i].Eval (domain);
-		  if (domain.Thrown)
+		  if (domain.Thrown ())
 		    return result;
 		}
 	    } finally {
@@ -1511,7 +1684,7 @@ namespace System.Xml.Expression
 
     private static Term Fquote (Domain domain, Variable vari, Term[] args)
     {
-      return new Term (args[0]);
+      return args[0];
     }
 
     private static Term Ftype (Domain domain, Variable vari, Term[] args)
@@ -1530,111 +1703,145 @@ namespace System.Xml.Expression
     public static Term Fcatch (Domain domain, Variable vari, Term[] args)
     {
       Term result = Zero;
-      try {
-	domain.Catch (new CatchTag (args[0].Symval));
-	result = args[1].Eval (domain);
-      } finally {
-	domain.Uncatch ();
-      }
-      return result;
+      bool caught;
+
+      domain.Catch (new CatchTag (args[0].Symval));
+      for (int i = 1; i < args.Length; i++)
+	{
+	  result = args[i].Eval (domain);
+	  if (domain.Thrown (out caught))
+	    {
+	      domain.Uncatch ();
+	      if (caught)
+		{
+		  if (vari != null)
+		    vari.Value = result;
+		  return One;
+		}
+	      return result;
+	    }
+	}
+      domain.Uncatch ();
+      if (vari != null)
+	vari.Value = result;
+      return Zero;
     }
 
     public static Term Fthrow (Domain domain, Variable vari, Term[] args)
     {
-      domain.ThrowTag (new CatchTag (args[0].Symval));
-      return (args.Length == 1 ? Zero : args[1]);
+      if (args[0].IsSymbol)
+	{
+	  domain.ThrowSymbol (args[0]);
+	  return (args[args.Length - 1]);
+	}
+      if (args[0].IsError)
+	return domain.ThrowError (args[0]);
+      return domain.ThrowError (new Term (Error.InvalidArgumentType,
+					  args[0].ToString ()));
     }
 
-    public delegate TermValue TermParser (Domain domain, XmlNode node);
+    public abstract class TermValue
+    {
+      public virtual Term Eval (Domain domain) { return new Term (this); }
+      public virtual TermValue Clone () { return this; }
+      public virtual bool IsTrue { get { return true; } }
+      public virtual bool Matches (TermValue other) { return Equals (other); }
+      public override abstract bool Equals (object obj);
+      public override abstract int GetHashCode ();
+      public abstract string ToString (bool detail);
+    }
 
-    public class TermType
+    private class Varref : TermValue
     {
-      public readonly Symbol type;
-      internal readonly TermParser parser;
+      private static Symbol name = "varref";
+      public static Symbol Name { get { return name; } }
+
+      private Symbol vname;
+      private Variable vari;
 
-      public TermType (Symbol type, TermParser parser)
+      public Varref (Symbol vname) { this.vname = vname; }
+
+      public override Term Eval (Domain domain)
       {
-	this.type = type;
-	this.parser = parser;
+	if (vari == null || vari.domain != domain)
+	  vari = domain.GetVar (vname, true);
+	return vari.Value;
       }
-    }
 
-    public abstract class TermValue
-    {
-      public virtual Term Eval (Domain domain) { return new Term (this); }
-      public virtual TermValue Clone () { return this; }
+      public static TermValue Parser (Domain domain, XmlNode node)
+      {
+	return new Varref ((Symbol) node.Attributes[Qvname].Value);
+      }
+
+      public override bool Equals (object obj)
+      {
+	Varref varref = obj as Varref;
+	return (varref != null && varref.vari.name == vari.name);
+      }
+
+      public override int GetHashCode ()
+      {
+	return vari.name.GetHashCode ();
+      }	
+
+      public override string ToString () { return ToString (true); }
+
+      public override string ToString (bool detail)
+      {
+	return "<varref vname=\"" + vname + "\"/>";
+      }
     }
 
     private class Funcall : TermValue
     {
+      private static Symbol name = "funcall";
+      public static Symbol Name { get { return name; } }
+
       internal Function func;
       internal Variable vari;
       internal Term[] args;
 
-      private Funcall (Function func, Variable vari, Term[] args)
+      public Funcall (Function func, Variable vari, Term[] args)
 	{
+	  int nargs = args.Length;
+
+	  if (nargs < func.min_arg
+	      || (func.max_arg >= 0 && nargs > func.max_arg))
+	    throw_exception ("Invalid number of arguments to {0}: ",
+			     func.name, nargs);
+	  if (! func.setvar && vari != null)
+	    throw_exception ("vname attribute not acceptable: ", func.name);
 	  this.func = func;
 	  this.vari = vari;
 	  this.args = args;
 	}
 
-      public Funcall (Domain domain, Symbol fname, Term[] args)
-	{
-	  func = domain.GetFunc (fname);
-	  if (args != null)
-	    {
-	      int nargs = args.Length;
-	      if (nargs < func.min_arg
-		  || (func.max_arg >= 0 && nargs > func.max_arg))
-		throw new Exception ("Invalid number of arguments to: "
-				     + fname + " " + nargs);
-	    }
-	  this.args = args;
-	}
-
-      public Funcall (Domain domain, Symbol fname, Symbol vname, Term[] args)
-	{
-	  func = domain.GetFunc (fname);
-	  if (args != null)
-	    {
-	      int nargs = args.Length;
-	      if (nargs < func.min_arg
-		  || (func.max_arg >= 0 && nargs > func.max_arg))
-		throw new Exception ("Invalid number of arguments to: "
-				     + fname + " " + nargs);
-	    }
-	  this.args = args;
-	  if (vname != Qnull)
-	    vari = domain.GetVar (vname, true);
-	}
+      public static TermValue Parser (Domain domain, XmlNode node)
+      {
+	Symbol fname = node.Name;
+	XmlAttribute attr;
 
-      internal static TermValue parser (Domain domain, XmlNode node)
-	{
-	  Symbol fname = node.Name;
-	  Symbol vname = Qnull;
-	  XmlAttribute attr;
-
-	  if (fname == Qfuncall)
-	    fname = node.Attributes[Qfname].Value;
-	  attr = node.Attributes[Qvname];
-	  if (attr != null)
-	    vname = attr.Value;
-
-	  XmlNodeList nlist = node.ChildNodes;
-	  int nargs = nlist.Count;
-	  Term[] args = new Term[nargs];
-	  for (int i = 0; i < nargs; i++)
-	    args[i] = new Term (domain, nlist[i]);
-	  return new Funcall (domain, fname, vname, args);
-	}
+	if (fname == Qfuncall)
+	  fname = node.Attributes[Qfname].Value;
+	Function func = domain.GetFunc (fname);
+	Variable vari;
+	attr = node.Attributes[Qvname];
+	vari = attr == null ? null : domain.GetVar (attr.Value, true);
+	XmlNodeList nlist = node.ChildNodes;
+	int nargs = nlist.Count;
+	Term[] args = new Term[nargs];
+	for (int i = 0; i < nargs; i++)
+	  args[i] = new Term (domain, nlist[i]);
+	return new Funcall (func, vari, args);
+      }
 
       public override Term Eval (Domain domain)
       {
-	domain.DebugWrite (true, ToString ());
+	domain.TraceWrite (ToString ());
 	domain.depth++;
 	Term result = func.Call (domain, vari, args);
 	domain.depth--;
-	domain.DebugWrite (true, " ==> {0})", result.ToString ());
+	domain.TraceWrite ("=> {0}", result.ToString ());
 	return result;
       }
 
@@ -1643,16 +1850,35 @@ namespace System.Xml.Expression
 	return new Funcall (func, vari, args);
       }
 
-      public override string ToString ()
+      public override bool Equals (object obj)
+      {
+	Funcall funcall = obj as Funcall;
+	return (obj != null
+		&& funcall.func == func
+		&& funcall.vari == vari
+		&& funcall.args.Length == args.Length);
+      }
+
+      public override int GetHashCode ()
+      {
+	return func.GetHashCode () ^ args.Length;
+      }
+
+      public override string ToString () { return ToString (true); }
+
+      public override string ToString (bool detail)
       {
 	string str = "<" + func.name;
 	if (vari != null)
 	  str += " vname=\"" + vari.name + "\"";
-	if (args == null)
+	if (args.Length == 0 || ! detail)
 	  return str + "/>";
 	str += ">";
 	if (func is Function.SpecialForm)
-	  str += "...";
+	  {
+	    for (int i = 0; i < args.Length; i++)
+	      str += ".";
+	  }
 	else
 	  foreach (Term e in args)
 	    str += e;
@@ -1660,6 +1886,75 @@ namespace System.Xml.Expression
       }
     }
 
+    internal class ErrorTerm : TermValue
+    {
+      private static Symbol name = "error";
+      public static Symbol Name { get { return name; } }
+      
+      private readonly Symbol ename;
+      private string message;
+      private Term[] stack;
+
+      public ErrorTerm (Symbol ename, string message)
+	{
+	  this.ename = ename;
+	  this.message = message;
+	}
+
+      public static TermValue Parser (Domain domain, XmlNode node)
+      {
+	XmlAttribute attr = node.Attributes[Qename];
+	Symbol ename = attr == null ? Qnull : (Symbol) attr.Value;
+	string message = node.InnerText;
+	return new ErrorTerm (ename, message);
+      }
+
+      public Term[] CallStack {	get { return stack; } set { stack = value; } }
+
+      public override TermValue Clone ()
+      {
+	return new ErrorTerm (ename, message);
+      }
+
+      public override bool Equals (object obj)
+      {
+	ErrorTerm e = obj as ErrorTerm;
+	if (e == null || e.ename != ename || e.message != message
+	    || (e.stack == null ? stack != null
+		: (stack == null || e.stack.Length != stack.Length)))
+	  return false;
+	if (stack != null)
+	  for (int i = 0; i < stack.Length; i++)
+	    if (! stack[i].Equals (e.stack[i]))
+	    return false;
+	return true;
+      }
+
+      public override int GetHashCode ()
+      {
+	return ename.GetHashCode ();
+      }
+
+      public override bool Matches (TermValue term)
+      {
+	ErrorTerm e = term as ErrorTerm;
+	return (e != null && (ename == Qnull || e.ename == ename));
+      }
+
+      public override string ToString () { return ToString (true); }
+
+      public override string ToString (bool detail)
+	{
+	  string str = "<error type=\"" + ename + "\">";
+	  if (message != null)
+	    str += message;
+	  if (stack != null)
+	    for (int i = 0; i < stack.Length; i++)
+	      str += stack[i].ToString (false);
+	  return str + "</error>";
+	}
+    }
+
     public struct Term
     {
       public int intval;
@@ -1673,8 +1968,13 @@ namespace System.Xml.Expression
       public Term (string str) { intval = 0; objval = str; }
       // <list>...</list>
       public Term (List<Term> list) { intval = 0; objval = list; }
+      // <error ename="ERROR-NAME">ERROR-MESSASGE</error>
+      public Term (Symbol name, string message)
+	{
+	  intval = 0;
+	  objval = new ErrorTerm (name, message);
+	}
 
-      public Term (Term term) { intval = term.intval; objval = term.objval; }
       public Term (TermValue obj) { intval = 0; objval = obj; }
 
       public Term (Domain domain, XmlNode node)
@@ -1693,8 +1993,6 @@ namespace System.Xml.Expression
 		objval = (Symbol) node.InnerText;
 	      else if (name == Qstring)
 		objval = node.InnerText.Clone ();
-	      else if (name == Qvarref)
-		objval = domain.GetVar ((Symbol) node.Attributes[0].Value, true);
 	      else if (name == Qlist)
 		{
 		  List<Term> list = new List<Term> ();
@@ -1705,12 +2003,22 @@ namespace System.Xml.Expression
 		}
 	      else
 		{
-		  TermType term_type;
+		  MethodInfo minfo;
 
-		  if (domain.termtypes.TryGetValue (name, out term_type))
-		    objval = term_type.parser (domain, node);
+		  if (domain.termtypes.TryGetValue (name, out minfo))
+		    objval = (TermValue) minfo.Invoke (null, new Object[] { domain, node});
 		  else
-		    objval = Funcall.parser (domain, node);
+		    {
+		      Funcall funcall = (Funcall) Funcall.Parser (domain, node);
+		      if (funcall.func is Function.Macro)
+			{
+			  Term result = funcall.Eval (domain);
+			  intval = result.intval;
+			  objval = result.objval;
+			}
+		      else
+			objval = funcall;
+		    }
 		}
 	    }
 	}
@@ -1719,21 +2027,29 @@ namespace System.Xml.Expression
       public Term (Domain domain, Symbol vname)
 	{
 	  intval = 0;
-	  objval = domain.GetVar (vname, true);
+	  objval = new Varref (vname);
 	}
 
       // <funcall fname="FNAME">...</funcall>
       public Term (Domain domain, Symbol fname, Term[] args)
-	{
-	  intval = 0;
-	  objval = new Funcall (domain, fname, args);
-	}
+	: this (domain, fname, Qnull, args) { }
 
       // <funcall fname="FNAME" vname="VNAME">...</funcall>
       public Term (Domain domain, Symbol fname, Symbol vname, Term[] args)
 	{
 	  intval = 0;
-	  objval = new Funcall (domain, fname, vname, args);
+
+	  Function func = domain.GetFunc (fname);
+	  Variable vari = vname == Qnull ? null : domain.GetVar (vname, true);
+	  Funcall funcall = new Funcall (func, vari, args);
+	  if (func is Function.Macro)
+	    {
+	      Term result = funcall.Eval (domain);
+	      intval = result.intval;
+	      objval = result.objval;
+	    }
+	  else
+	    objval = funcall;
 	}
 
       public object Objval {
@@ -1755,7 +2071,7 @@ namespace System.Xml.Expression
       public string Strval {
 	get {
 	  if (! IsStr)
-	    throw new Exception ("term is not string: " + this);
+	    throw new Exception ("term is not a string: " + this);
 	  return (string) objval;
 	}
       }
@@ -1763,7 +2079,7 @@ namespace System.Xml.Expression
       public string Symval {
 	get {
 	  if (! IsSymbol)
-	    throw new Exception ("term is not symbol: " + this);
+	    throw new Exception ("term is not a symbol: " + this);
 	  return (Symbol) objval;
 	}
       }
@@ -1771,7 +2087,7 @@ namespace System.Xml.Expression
       public List<Term> Listval {
 	get {
 	  if (! IsList)
-	    throw new Exception ("term is not list: " + this);
+	    throw new Exception ("term is not a list: " + this);
 	  return (List<Term>) objval;
 	}
       }
@@ -1782,27 +2098,29 @@ namespace System.Xml.Expression
 		  ? (intval != 0)
 		  : objval is List<Term>
 		  ? (((List<Term>) objval).Count != 0)
+		  : objval is TermValue
+		  ? ((TermValue) objval).IsTrue
 		  : true);
 	}
       }
+
       public bool IsInt { get { return (objval == null); } }
       public bool IsStr { get { return (objval is string); } }
       public bool IsSymbol { get { return (objval is Symbol); } }
       public bool IsList { get { return (objval is List<Term>); } }
-
-      public bool IsType (Type type)
-      {
-	return (objval == null ? type == typeof (int)
-		: type == objval.GetType ());
-      }
+      public bool IsError { get { return (objval is ErrorTerm); } }
 
       public Term Eval (Domain domain)
       {
-	if (objval == null || objval is Symbol || objval is string)
-	  return this;
-	if (objval is List<Term>)
-	  return new Term ((List<Term>) objval);
-	return ((TermValue) objval).Eval (domain);
+	try {
+	  domain.PushTerm (this);
+	  if (objval == null || objval is Symbol || objval is string
+	      || objval is List<Term>)
+	    return this;
+	  return ((TermValue) objval).Eval (domain);
+	} finally {
+	  domain.PopTerm ();
+	}
       }
 
       public Term Clone ()
@@ -1818,7 +2136,60 @@ namespace System.Xml.Expression
 	return new Term (((TermValue) objval).Clone ());
       }
 
-      public override string ToString ()
+      public static bool operator== (Term t1, Term t2)
+	{
+	  return t1.Equals (t2);
+	}
+
+      public static bool operator!= (Term t1, Term t2) { return ! (t1 == t2); }
+
+      public override bool Equals (object obj)
+      {
+	if (! (obj is Term))
+	  return false;
+	Term term = (Term) obj;
+	if (IsInt)
+	  return term.IsInt && term.Intval == Intval;
+	if (IsStr)
+	  return term.IsStr && term.Strval == Strval;
+	if (IsSymbol)
+	  return term.IsSymbol && term.Symval == Symval;
+	if (IsList)
+	  {
+	    if (! term.IsList)
+	      return false;
+	    List<Term> l1 = objval as List<Term>;
+	    List<Term> l2 = term.objval as List<Term>;
+
+	    if (l1.Count != l2.Count)
+	      return false;
+	    for (int i = 0; i < l1.Count; i++)
+	      if (! l1[i].Equals (l2[i]))
+		return false;
+	    return true;
+	  }
+	return ((TermValue) objval).Equals (obj);
+      }
+
+      public override int GetHashCode () { return intval; }
+
+      public bool Matches (Term term)
+      {
+	if (IsInt)
+	  return term.IsInt && term.Intval == Intval;
+	if (IsStr)
+	  return term.IsStr && term.Strval == Strval;
+	if (IsSymbol)
+	  return term.IsSymbol && term.Symval == Symval;
+	if (IsList)
+	  return (((List<Term>) objval).Count > 0
+		  && ((List<Term>) objval)[0].Matches (term));
+	return ((TermValue) objval).Matches ((TermValue) term.objval);
+      }
+
+      public override string ToString () { return ToString (true); }
+
+      public string ToString (bool detail)
       {
 	string str;
 
@@ -1830,15 +2201,20 @@ namespace System.Xml.Expression
 	  str = "<string>" + objval + "</string>";
 	else if (objval is List<Term>)
 	  {
-	    str = "<list>";
-	    foreach (Term e in (List<Term>) objval)
-	      str += e;
-	    str += "</list>";
+	    if (detail)
+	      {
+		str = "<list>";
+		foreach (Term e in (List<Term>) objval)
+		  str += e;
+		str += "</list>";
+	      }
+	    else
+	      str = "<list/>";
 	  }
 	else if (objval is Term)
 	  str = "<quote>" + objval + "</quote>";
 	else if (objval is TermValue)
-	  str = ((TermValue) objval).ToString ();
+	  str = ((TermValue) objval).ToString (detail);
 	else
 	  throw new Exception ("invalid Term object: " + objval);
 	return str;
@@ -1912,6 +2288,8 @@ namespace System.Xml.Expression
 	  {
 	    if (n.Name == Qdefun)
 	      domain.Defun (n, true);
+	    else if (n.Name == Qdefmacro)
+	      domain.Defmacro (n, true);
 	    else if (n.Name == Qdefvar)
 	      domain.Defvar (n);
 	    else
@@ -1924,6 +2302,8 @@ namespace System.Xml.Expression
 	  {
 	    if (n.Name == Qdefun)
 	      domain.Defun (n, false);
+	    else if (n.Name == Qdefmacro)
+	      domain.Defmacro (n, false);
 	    else if (n.Name != Qdefvar)
 	      terms[i++]= new Term (domain, n);
 	  }
@@ -1950,10 +2330,10 @@ namespace System.Xml.Expression
 
     public Xexpression (Domain domain, string url)
     {
-      XmlDocument doc = new XmlDocument (Symbol.Table);
+      XmlDocument doc = new XmlDocument (Symbol.NameTable);
       XmlNode node;
 
-      using (XmlTextReader reader = new XmlTextReader (url, Symbol.Table))
+      using (XmlTextReader reader = new XmlTextReader (url, doc.NameTable))
 	{
 	  do {
 	    reader.Read ();
@@ -1977,7 +2357,7 @@ namespace System.Xml.Expression
 	foreach (Term term in terms)
 	  {
 	    result = term.Eval (domain);
-	    if (domain.Thrown)
+	    if (domain.Thrown ())
 	      return result;
 	  }
       } finally {