// $Id: Parser.cs 83 2003-06-21 08:03:35Z mdupont $
// PxButton | build | csc /o /doc:Euler.xml *.cs |

using System;
using System.Collections;
using System.Text;

// for stack trace!
using System.Diagnostics;
using System.Reflection; 

/// <summary>N3 parser</summary>
/// <author>Jos De Roo</author>

public class Parser {
  internal String str;                      // N3 string
  internal int pos = 0;                     // tokenizer position
  internal ArrayList vt = null;             // quantified variables table
  internal Euler r = null;                  // root Euler object
  internal String u = null;                 // base URI of the RDF resource
  
  internal const String ST = "{}[]()<>\"';,.^! \t\r\n\\";
  internal const String LOGa = "a";
  internal const String LOGe = "=";
  internal const String LOGi = "=>";
  internal const String LOGimplies = "<http://www.w3.org/2000/10/swap/log#implies>";
  internal const String LOGnotImplies = "<http://www.w3.org/2000/10/swap/log#notImplies>";
  internal const String DPO = "<http://www.daml.org/2001/03/daml+oil";
  internal const String ONT = "<http://www.w3.org/2001/10/daml+oil";
  internal const String OWL = "<http://www.w3.org/2002/07/owl";
  internal const String OWLequivalentTo = "<http://www.w3.org/2002/07/owl#equivalentTo>";
  internal const String OWLsameIndividualAs = "<http://www.w3.org/2002/07/owl#sameIndividualAs>";
  internal const String OWLsameAs = "<http://www.w3.org/2002/07/owl#sameAs>";
  internal const String OWLsameClassAs = "<http://www.w3.org/2002/07/owl#sameClassAs>";
  internal const String OWLequivalentClass = "<http://www.w3.org/2002/07/owl#equivalentClass>";
  internal const String OWLsamePropertyAs = "<http://www.w3.org/2002/07/owl#samePropertyAs>";
  internal const String OWLequivalentProperty = "<http://www.w3.org/2002/07/owl#equivalentProperty>";
  internal const String OWLdifferentIndividualFrom = "<http://www.w3.org/2002/07/owl#differentIndividualFrom>";
  internal const String OWLdifferentFrom = "<http://www.w3.org/2002/07/owl#differentFrom>";
  internal const String OWLFunctionalProperty = "<http://www.w3.org/2002/07/owl#FunctionalProperty>";
  internal const String OWLInverseFunctionalProperty = "<http://www.w3.org/2002/07/owl#InverseFunctionalProperty>";
  internal const String OWLUnambiguousProperty = "<http://www.w3.org/2002/07/owl#UnambiguousProperty>";
  internal const String OWLUniqueProperty = "<http://www.w3.org/2002/07/owl#UniqueProperty>";
  internal const String XSDstring = "<http://www.w3.org/2001/XMLSchema#string>";
  internal const String RDFtype = "<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>";
  internal const String RDFList = "<http://www.w3.org/1999/02/22-rdf-syntax-ns#List>";
  internal const String RDFfirst = "<http://www.w3.org/1999/02/22-rdf-syntax-ns#first>";
  internal const String RDFrest = "<http://www.w3.org/1999/02/22-rdf-syntax-ns#rest>";
  internal const String RDFnil = "<http://www.w3.org/1999/02/22-rdf-syntax-ns#nil>";
  
  /// <summary>constructs an N3 parser</summary>

  static int instancecount = 0;
  int instance = 0;

  public Parser() {
      instance = instancecount++;
  }
  
  /// <summary>constructs an N3 parser</summary>
  /// <param name="s">the N3 string</param>
  /// <param name="vartab">quantified variables table</param>
  /// <param name="root">Euler object</param>
  /// <param name="uri">URI of the RDF resource</param>

  public Parser(String s, ArrayList vartab, Euler root, String uri) {
      instance = instancecount++;

    str = s;
    vt = vartab;
    r = root;
    u = uri;
  }
  
  /// <summary>N3 triple parse method</summary>
  /// <returns>Euler object</returns>

  public virtual Euler Parse() {
    String nt = tokenize();
    if (nt == null) return null;
    return parse(true, nt);
  }
  
  /// <summary>N3 node parse method</summary>
  /// <param name="nt">next token</param>
  /// <returns>Euler object</returns>

  public virtual Euler Parse(String nt) {

      Console.Error.WriteLine ("  public virtual Euler Parse(String nt)");
    return parse(false, nt);

  }


  internal Euler parse(bool b, String nt) {

      Console.Error.WriteLine ("internal Euler parse(bool b, String nt)");

      Console.Error.WriteLine ("parser  stack" + instance);

      StackTrace st = new  System.Diagnostics.StackTrace(true);       
      for(int i = 0; i < st.FrameCount; i ++)
	  {
	      StackFrame sf = st.GetFrame(i);
	      Debug.WriteLine(" File: " +  sf.GetFileName()  +
			      " Line: "  + sf.GetFileLineNumber() + 
			      " Method: " + sf.GetMethod());
	  } 
      Console.Error.WriteLine ("parser end of stack");
      
      Euler e = new Euler();

      Console.Error.WriteLine ("new euler");

    try {
      if (b) {

	  Console.Error.WriteLine ("ifb");



        if (nt == null) 
	    {
		Console.Error.WriteLine ("if nt == null");

		e.subj = null;
	    }
        else if (nt.Equals("{")) 
	    {

		Console.Error.WriteLine ("if nt == {");

		Console.Error.WriteLine ("before tokenize");

		nt = tokenize();

		if (nt.Equals(".")) {
		    
		    Console.Error.WriteLine ("if nt == .");

		    Console.Error.WriteLine ("going to recurse");

		    e.subj = parse(false, "{}");

		    Console.Error.WriteLine ("after recurse");


		}
		else 
		    {
		    Console.Error.WriteLine ("else");

		    Console.Error.WriteLine ("going to recurse2");
			e.subj = parse(true, nt);
		    Console.Error.WriteLine ("after recurse2");
		    }

		Euler el = e.subj;
		Console.Error.WriteLine ("before tokenize2");
		nt = tokenize();
		Console.Error.WriteLine ("after tokenize2");



          while (el.near != null) {
	      el = el.near;
	  }


          while (!nt.Equals("}")) {

	      Console.Error.WriteLine ("going to recurse 3");
            el.near = parse(true, nt);
	      Console.Error.WriteLine ("after recurse 3");

            while (el.near != null) 
		{
		    el = el.near;
		}

            nt = tokenize();

          }
        }
        else if (nt.Equals("[")) {

	    Console.Error.WriteLine ("recurse 4");	    
	    e.subj = parse(true, null);
	    Console.Error.WriteLine ("~recurse 4");

          if (e.subj.verb == null) r.verb = ";]";
          nt = tokenize();

          if (!nt.Equals("]")) Console.Error.WriteLine("** (p1) expecting ] at " + e + " but got " + nt);
        }
        else if (nt.Equals("(")) {
          list(e);
          e.subj = e.obj;
          e.obj = null;
        }
        else {
	    Console.Error.WriteLine ("recurse 5");	    
	    e.subj = parse(false, nt);
	    Console.Error.WriteLine ("~recurse 5");	    

          if (nt.Equals("this")) e.subj.verb = '<' + u + "#frag" + e.GetHashCode() + '>';
        }
        nt = tokenize();
      }


      Console.Error.WriteLine ("after ifb");

      //// ------------------------


      if (nt == null || nt.Equals(";")) {
	  Console.Error.WriteLine ("nt = ;");

        e.bound = true;
	
	Console.Error.WriteLine ("Parser:Return1");

        return e;
      }
      else if (e.subj != null && nt.StartsWith("_:")) {

	  // verb handler!
	  Console.Error.WriteLine ("nt =~ _:");

	  e.cverb = nt;
	  if (!vt.Contains(nt)) vt.Add(nt);

      }
      else if (nt.Equals("[")) {

	  // verb handler!
	  Console.Error.WriteLine ("nt = [");

        String a = "_:" + e.GetHashCode();
        if (!vt.Contains(a)) vt.Add(a);

	Console.Error.WriteLine ("recurse 6");

        Euler ap = parse(true, a);

	Console.Error.WriteLine ("~recurse 6");

        e.cverb = a;
        if (ap.verb != null) r.verb = ";]";
        nt = tokenize();
        if (!nt.Equals("]")) Console.Error.WriteLine("** (p2) expecting ] at " + e + " but got " + nt);
        e.near = ap;
      }
      else if (nt.Equals("(")) {
	  Console.Error.WriteLine ("nt = (");
	  list(e);

	  Console.Error.WriteLine ("Parser:Return2");

	  return e.obj;
      }
      else {
	  Console.Error.WriteLine ("else e.cverb = nt;");

	  e.cverb = nt;
      }

     //------------------------------
      Console.Error.WriteLine ("ok, copy verb");
      e.verb = e.cverb;
      if (e.verb.EndsWith("@@")) e.verb = e.verb.Substring(0, e.verb.Length - 2);
      String s1 = e.verb;
      String s2 = "";
	
//      Console.Error.WriteLine("e.verb index of " + e.verb);	
      if (e.verb.IndexOf('"') != -1) {
        s1 = e.verb.Substring(0, e.verb.IndexOf('"'));
        s2 = e.verb.Substring(e.verb.IndexOf('"'));
      }

      if (r != null && s1.Length > 0 && !s1.Equals(LOGa) && !s1.Equals(LOGe) &&
          s1[0] != '(' && s1[0] != '<' && s1[0] != '[' &&
          s1[0] != '_' && s1[0] != '"' && s1[0] != '\'' && s1.IndexOf(':') != - 1) {
        String pf = s1.Substring(0, s1.IndexOf(':') + 1);

        String pg = (String) r.hshtNsp[pf]; // TODO check

        if (pg != null) pf = pg;
        String qf = (String) r.hshtNs[pf];
        if (qf == null) {
          Console.Error.WriteLine("** no @prefix " + pf + " found, taking <" + u + "#>");
          qf = "<" + u + "#>";
          r.hshtNs[pf] = qf;
        }
        StringBuilder sb = new StringBuilder(pf);

//	Console.Error.WriteLine("e.cverb.IndexOf " + e.cverb);	

        sb.Append(e.cverb.Substring(e.cverb.IndexOf(':') + 1));
        e.cverb = sb.ToString();
        sb = new StringBuilder(qf);
        sb.Insert(sb.Length - 1, s1.Substring(s1.IndexOf(':') + 1));
        e.verb = sb.ToString() + s2;
      }
      else if (u != null && s1.Length > 0 && s1[0] == '<' && s1.IndexOf(':') == - 1)
        e.verb = e.cverb = '<' + toURI(s1.Substring(1, s1.Length - 2)) + '>' + s2;



      //TODO see    ParseSpecials();

      if (e.verb.StartsWith("?") && !vt.Contains(e.verb)) vt.Add(e.verb);
	
      if (vt != null)
	{
//	 Console.Error.WriteLine("TODO: This broken");	
//	Console.Error.WriteLine("count  " + count);	
	int count = vt.Count;

	
	if (count > 0)
	{
//		 Console.Error.WriteLine("e.varid = vt.IndexOf(e.verb); " + vt +":"+ e.verb);	
//		 e.varid = vt.IndexOf(e.verb);
	}
	}	
      if (e.varid == - 1) e.bound = true;
      if (nt.Equals(".")) {

	  Console.Error.WriteLine ("going to recurse 7");

        e.obj = parse(false, "");
	  Console.Error.WriteLine ("~ recurse 7");
        e.verb = "";
        e.cverb = "";
        e.bound = true;

	Console.Error.WriteLine ("Parser:Return3");

        return e;
      }
      if (str != null && pos < str.Length && str[pos] == '^' && str[pos + 1] == '^') {
        pos = pos + 2;

	Console.Error.WriteLine ("going to recurse 8");
        Euler et = parse(false, tokenize());
	Console.Error.WriteLine ("~going to recurse 8");

        if (!et.verb.Equals(XSDstring)) {
          e.subj = e.copy();
          e.verb = e.cverb = "^^";
          e.bound = true;
          e.obj = et;
          String.Intern(e.obj.verb);

          if (e.subj.bound) 
		{	
		//TODO	Datatype.Compare(e.obj.verb, r.getLit(e.subj), r.getLit(e.subj));
		}	
        }
      }

      //---------------------------------
      Console.Error.WriteLine ("before if b");

      if (b) {
// 	  Console.Error.WriteLine ("if b");
// 	  nt = tokenize();
// 	  if (nt.Equals("{")) {
// 	      nt = tokenize();


// 	      Console.Error.WriteLine ("going to recurse 9");

// 	      if (nt.Equals(".")) e.obj = parse(false, "{}");
// 	      else e.obj = parse(true, nt);

// 	      Console.Error.WriteLine ("~recurse 9");

// 	      Euler el = e.obj;
// 	      nt = tokenize();
// 	      while (nt != null && !nt.Equals("}")) {

// 		  Console.Error.WriteLine ("going to recurse 10");

// 		  el.near = parse(true, nt);

// 		  Console.Error.WriteLine ("~recurse 10");

// 		  el = el.near;
// 		  nt = tokenize();
// 	      }
// 	  }
// 	  else if (nt.Equals("[")) {
// 		  Console.Error.WriteLine ("going to recurse 11");
// 	      e.obj = parse(true, null);
// 		  Console.Error.WriteLine ("~recurse 11");
// 	      if (e.obj.verb != null) r.verb = ";]";
// 	      nt = tokenize();
// 	      if (!nt.Equals("]")) Console.Error.WriteLine("** (p3) expecting ] at " + e + " but got " + nt);
// 	  }
// 	  else if (nt.Equals("(")) list(e);
// 	  else {
// 		  Console.Error.WriteLine ("recurse 12");
// 		  e.obj = parse(false, nt);
// 		  Console.Error.WriteLine ("~recurse 12");
// 	      if (e.obj.verb.Equals(OWLFunctionalProperty)) 
// 		{		
// 		  int x= e.subj.verb;	     
// 		  r.hshtMto[x] = r;
// 		}	

// 	      if (e.obj.verb.Equals(OWLInverseFunctionalProperty)) r.hshtOtm[e.subj.verb] = r;
// 	  }

	  
// 	  nt = tokenize();
// 	  if (nt.EndsWith("\"\"\"")) 

{
          e.obj.cverb = e.obj.cverb + nt;
          e.obj.verb = e.obj.cverb;
          nt = tokenize();
	  }

        Euler el2 = e;
        while (nt.Equals(";") || nt.Equals(",")) {
          while (el2.near != null) el2 = el2.near;
          if (nt.Equals(";")) {
            nt = tokenize();
            if (nt.Equals("]")) {
              r.verb = ";]";
              nt = ";";
              break;
            }
            else if (nt.Equals(".")) break;
          }
          else nt = el2.cverb;
	  Console.Error.WriteLine ("going to recurse 13");
	  el2.near = parse(false, nt);
	  Console.Error.WriteLine ("~ recurse 13");
          el2.near.subj = e.subj;
          nt = tokenize();
          if (nt.Equals("{")) {
            nt = tokenize();

	  Console.Error.WriteLine ("going to recurse 14");
            if (nt.Equals(".")) el2.near.obj = parse(false, "{}");
            else el2.near.obj = parse(true, nt);
	  Console.Error.WriteLine ("~recurse 14");

            Euler ef = el2.near.obj;
            nt = tokenize();
            while (nt != null && !nt.Equals("}")) {

	  Console.Error.WriteLine ("going to recurse 15");
              ef.near = parse(true, nt);
	  Console.Error.WriteLine ("~recurse 15");

              ef = ef.near;
              nt = tokenize();
            }
          }
          else if (nt.Equals("[")) {

	  Console.Error.WriteLine ("going to recurse 16");
            el2.near.obj = parse(true, null);
	  Console.Error.WriteLine ("~recurse 16");

            if (el2.near.obj.verb != null) r.verb = ";]";
            nt = tokenize();
            if (!nt.Equals("]")) Console.Error.WriteLine("** (p4) expecting ] at " + e + " but got " + nt);
          }
          else if (nt.Equals("(")) list(el2.near);
          else {


	  Console.Error.WriteLine ("going to recurse 17");
	  Euler returnv = parse(false, nt);	 
	  Console.Error.WriteLine ("~recurse 17~");

	  Console.Error.WriteLine (" before set");
	  el2.near.obj = returnv;
	  Console.Error.WriteLine (" after set");


	  //            if (el2.near.obj.verb.Equals(OWLFunctionalProperty)) r.hshtMto[el2.near.subj.verb] = r;
          //  if (el2.near.obj.verb.Equals(OWLInverseFunctionalProperty)) r.hshOtm[el2.near.subj.verb] = r;
          }
          nt = tokenize();
          if (nt.EndsWith("\"\"\"")) {
            el2.near.obj.cverb = el2.near.obj.cverb + nt;
            el2.near.obj.verb = el2.near.obj.cverb;
            nt = tokenize();
          }
          swap(el2.near);
        }
        if (!nt.Equals(".") && !nt.Equals(";"))
          Console.Error.WriteLine("** (p5) expecting . or ; at " + e + " but got " + nt);
      }

      Console.Error.WriteLine ("after if b");

      swap(e);
      e.far = r;

      Console.Error.WriteLine ("parser before return stack" );
      Console.Error.WriteLine ("parser instance" + instance);

      StackTrace st = new  System.Diagnostics.StackTrace(true);       
      for(int i = 0; i < st.FrameCount; i ++)
	  {
	      StackFrame sf = st.GetFrame(i);
	      Debug.WriteLine(" File: " +  sf.GetFileName()  +
			      " Line: "  + sf.GetFileLineNumber() + 
			      " Method: " + sf.GetMethod());
	  } 
      Console.Error.WriteLine ("parser before return");


      return e;
    }
    catch (NullReferenceException exc) {

      Console.Error.WriteLine ("catch");

      Console.Error.WriteLine(exc.StackTrace);
      Console.Error.WriteLine ("before return exception");
      return e;
    }
  }
  
  internal String tokenize() {
    String nt = token();
    while (pos < str.Length && nt == null) nt = token();
    return nt;
  }
  
  internal String next() {
    int start = pos;

//    Console.Error.WriteLine("ST.IndexOf(str[pos]) " + ST + ":" +str[pos] );	

    while (pos < str.Length && ST.IndexOf(str[pos]) < 0) {
	pos++;
//	Console.Error.WriteLine("ST.IndexOf(str[pos]) " + ST + ":" +str[pos] );	
    }	


    if (start == pos && ST.IndexOf(str[pos]) >= 0) pos++;

    Console.Error.WriteLine ("Parser::next going to return");

    return str.Substring(start, (pos) - (start));

  }
  
  internal String token() {

      Console.Error.WriteLine("Parser::Token()" );

    if (r.verb != null && r.verb.Equals(".}")) return r.verb = "}";
    if (r.verb != null && r.verb.Equals(";]")) return r.verb = "]";
    if (pos >= str.Length) return null;
    int start = pos;
    String t = null;
    String nt = next();


    Console.Error.WriteLine("token nt.IndexOf #" + nt);

    if (nt.IndexOf('#') != - 1) {
      t = nt.Substring(0, nt.IndexOf('#'));
      String v = r.verb;
      while (nt != null && !nt.Equals("\n") && pos < str.Length) nt = next();
      r.verb = v;
      if (t.Equals("")) return null;
    }
    else if (nt.Equals("@prefix") || nt.Equals("bind")) {
      String nsc = tokenize();
      if (nsc.Equals("default")) nsc = ":";
      String nsd = nsc;
      String nsu = tokenize();

//	    Console.Error.WriteLine("nsu.IndexOf #" + nsu);

      if (u != null && nsu.Length > 0 && nsu[0] == '<' && nsu.IndexOf(':') == - 1)
        nsu = '<' + toURI(nsu.Substring(1, nsu.Length - 2)) + '>';
      String nsv = (String) r.hshtNs[nsd];
      while (nsv != null && !nsu.Equals(nsv)) {
        nsd = "ns" + nsd;
        nsv = (String) r.hshtNs[nsd];
      }
      r.hshtNsp[nsd] = nsd; // TODO check
      r.hshtNsp[nsc] = nsd; // TODO check
      r.hshtNs[nsd] = nsu;
      tokenize();
      return null;
    }
    else if (nt.Equals("\"")) {
      StringBuilder sb = new StringBuilder("\"");
      if (str[pos] == '"' && str[pos+1] == '"') {
        sb.Append(next());
        sb.Append(next());
        while (true) {
          sb.Append(next());
          if (sb.ToString().EndsWith("\"\"\"")) break;
        }
        t = sb.ToString();
      }
      else {
        nt = next();
        while (!nt.Equals("\"")) {
          if (nt.Equals("\\")) {
            sb.Append(nt);
            nt = next();
          }
          sb.Append(nt);
          if (pos >= str.Length) {
            Console.Error.WriteLine("** (t1) expecting \" at " + sb);
            break;
          }
          nt = next();
        }
        sb.Append("\"");

//	    Console.Error.WriteLine("-@" + str[pos]);

        if ("-@".IndexOf(str[pos]) != -1) sb.Append(token().ToLower());
        t = sb.ToString();
      }
    }
    else if (nt.Equals("'")) {
      StringBuilder sb = new StringBuilder("'");
      nt = next();
      while (!nt.Equals("'")) {
        sb.Append(nt);
        if (pos >= str.Length) {
          Console.Error.WriteLine("** (t2) expecting ' at " + sb);
          break;
        }
        nt = next();
      }
      t = sb.Append("'").ToString();
    }
    else if (nt.Equals("<")) {
      StringBuilder sb = new StringBuilder("<");
      nt = next();
      while (!nt.Equals(">")) {
        sb.Append(nt);
        if (pos >= str.Length) {
          Console.Error.WriteLine("** (t2) expecting > at " + sb);
          break;
        }
        nt = next();
      }
      t = sb.Append(">").ToString();
    }
    else if (nt.Equals("=")) {
      if (str[pos] == '>') t = nt + next();
      else t = nt;
    }
    else if (nt.Equals("is")) {
      t = tokenize();
      nt = tokenize();
      if (!nt.Equals("of")) Console.Error.WriteLine("** (t4) expecting \"of\" but got " + nt);
      t = t + "@@";
    }
    else if (nt.Equals("has")) {
      t = tokenize();
      nt = tokenize();
      if (!nt.Equals("of")) Console.Error.WriteLine("** (t5) expecting \"of\" but got " + nt);
    }
    else if (nt.Equals(" ") || nt.Equals("\t") || nt.Equals("\r") || nt.Equals("\n") ||
             nt.Equals("-") || nt.Equals(">"))
      return null;
    else if (nt.StartsWith("_:") && !nt.EndsWith("_" + Euler.doc)) t = nt + "_" + Euler.doc;
    else t = nt;

//	Console.Error.WriteLine("ST . t " + ST + t);

    if (pos < str.Length && ST.IndexOf(t) == -1 && t[0] != '"' && str[pos] == '"')
      t = t + token();
    if (pos < str.Length && str[pos] == '.') {
      try {
	  Console.Error.WriteLine ("token call to parse" + t);

	  long ts = Int64.Parse(t);

	  Console.Error.WriteLine ("token parse returned");
	  t = ts + next() + next();
      }
      catch (Exception) {

	  Console.Error.WriteLine ("Token Caught exeception in parsing integer");
      }
    }
    Console.Error.WriteLine ("near end of Token()");

    if (r.verb != null && t != null && !r.verb.Equals(".") && t.Equals("}")) {
      r.verb = ".}";
      Console.Error.WriteLine ("Token:return .");

      return ".";
    }
    if (r.verb != null && t != null && !r.verb.Equals(";") && t.Equals("]")) {
      r.verb = ";]";
      Console.Error.WriteLine ("Token:return ;");
      return ";";
    }
    Console.Error.WriteLine ("Token:return r.verb = t;");
    return r.verb = t;
  }
  
  internal void swap(Euler e) {

      Console.Error.WriteLine ("Parser swap");

    if (e != null && e.subj == null && e.cverb.EndsWith("@@")) {
      e.subj = e.obj;

      Console.Error.WriteLine ("swap going to call parse");
      e.obj = parse(false, e.cverb.Substring(0, e.cverb.Length - 2));
      Console.Error.WriteLine ("swap ~ call parse");

      e.verb = e.cverb = "^^";
    }
    else if (e.subj != null && e.obj != null && e.cverb.EndsWith("@@")) {
      Euler el = e.subj;
      e.subj = e.obj;
      e.obj = el;
      e.cverb = e.cverb.Substring(0, e.cverb.Length - 2);
    }
  }
  
  internal void list(Euler e) {

      Console.Error.WriteLine ("parser_list");

    Euler el = e;
    while (true) {
      String nt = tokenize();
      if (nt.StartsWith("@")) {
      Console.Error.WriteLine ("list going to call parse");
        el.obj = parse(false, '?' + nt.Substring(1));
      Console.Error.WriteLine ("list ~call parse");
        nt = tokenize();
        if (!nt.Equals(")")) Console.Error.WriteLine("** (p6) expecting ) at " + el + " but got " + nt);
        break;
      }
      else if (nt.Equals(")")) {
        el.obj = parse(false, RDFnil);
        break;
      }
      else el.obj = parse(false, RDFfirst);
      if (nt.Equals("[")) {
        el.obj.obj = parse(true, null);
        tokenize();
      }
      else el.obj.obj = parse(false, nt);
      el.obj.near = parse(false, RDFrest);
      el.obj.near.near = parse(false, LOGa);      
      el.obj.near.near.obj = parse(false, RDFList);
      el = el.obj.near;
    }
  }

  internal String toURI(String s) {
    try {
      s = new Uri(new Uri(u), s).ToString();
    }
    catch (Exception e) {
      if (!u.StartsWith("file:")) Console.Error.WriteLine(u + " " + s + " " + e);
    }
    if (s.EndsWith(".n3#")) s = s.Substring(0, s.Length - 4) + "#";
    return s;
  }
}