ILexer

        TextRange ILexer.Parse(TextSnapshotRange snapshotRange, ILexerTarget parseTarget) {
            // 1. Prepare TextRange if needed
            int offsetStart = snapshotRange.StartOffset;
            int offsetEnd = snapshotRange.EndOffset;
            Debug.WriteLine("Parse text at "+offsetStart+" till "+offsetEnd);
            // 2. the lexer target where we would like to begin lexing at
            ILexerContext lexerContext = parseTarget.OnPreParse(ref offsetStart);
            Debug.WriteLine("Parse new OffsetStart: " + offsetStart);
            ILexicalScopeStateNode lexicalScope = new BlaiseLexicalScopeStateNode();
            // 3. start lexing
            // 3.1 prepare lexing
            Antlr.Runtime.IToken token = null;
            int pos = offsetStart;
            ITextBufferReader rdr = snapshotRange.Snapshot.GetReader(offsetStart).BufferReader;
            try {
                ParseInfo pi = _requestParseInfo();
                BlaiseLexer lexer = new Meta.Parsing.BlaiseLexer();
                // searchpaths
                foreach (string s in pi.IncludeSearchPath.Split(';')) { lexer.SearchPaths.Add(s); }
                // get the text
                string text = rdr.GetSubstring(offsetStart, offsetEnd - offsetStart);
                lexer.IncludeFile += new EventHandler<IncludeFileEventArgs>(DoIncludeFile);
                lexer.LoadText(text, pi.Filename);
                // 3.2 start lexing
                token = lexer.NextToken();
                bool resume = true;
                while (resume && token != null && token.Type != Mediator.EOF && pos<=offsetEnd) {

                    Antlr.Runtime.CommonToken at = token as Antlr.Runtime.CommonToken;
                    TextPosition endPos = snapshotRange.Snapshot.OffsetToPosition(at.Text.Length - 1 + pos);
                    TextPosition startPos = snapshotRange.Snapshot.OffsetToPosition(pos);
                    try {
                        if (token.Type == Mediator.ML_COMMENT)
                            ;
                        if (token.Type != Mediator.WS) { // skip WhiteSpace tokens
                            resume = parseTarget.OnTokenParsed(new BlaiseToken(token.Type, pos, token.Text.Length, startPos, endPos) , lexicalScope);
                        }
                    } catch (Exception ex){
                        Debug.WriteLine("Lexing: token lex failed " + ex.Message);
                    }
                    pos += token.Text.Length;
                    token = lexer.NextToken();
                }
                lexer.IncludeFile -= new EventHandler<IncludeFileEventArgs>(DoIncludeFile);
            } catch (Exception ex) {
                token = null;
                Debug.WriteLine("Lexing: complete lex failed " + ex.Message);
            }

            // 4. Send EndDocument Token fi end of file
            if (rdr.Length<= pos) {
                try {
                    BlaiseToken et = BlaiseToken.EndDocument(offsetEnd, 0, snapshotRange.Snapshot.OffsetToPosition(pos), snapshotRange.Snapshot.OffsetToPosition(pos));
                    parseTarget.OnTokenParsed(et, lexicalScope);
                } catch { }
            }
            // 5. notify end of lexing
            parseTarget.OnPostParse(pos);
            // 6. return
            return new TextRange(offsetStart, pos);
        }