示例#1
0
        static Token Scan(Buffer b, out bool error)
        {
            int startPosition = b.Position;
            char ch = b.GetCharacter();

            error = false;

            // CASE 1: Next token is a separator character
            if (ch == OpenParenthesis)
                return new Token(Token.Kind.Open, "(", startPosition);
            else if (ch == ClosedParenthesis)
                return new Token(Token.Kind.Close, ")", startPosition);
            if (ch == OpenBracket)
                return new Token(Token.Kind.LBracket, "(", startPosition);
            else if (ch == ClosedBracket)
                return new Token(Token.Kind.RBracket, ")", startPosition);
            else if (ch == Comma)
                return new Token(Token.Kind.Comma, ",", startPosition);
            // CASE 2: Next token is a quoted string
            else if (ch == QuoteChar)
            {
                StringBuilder stringToken = new StringBuilder();
                bool sawEscape = false;
                bool endOfString = false;
                while (!endOfString)
                {
                    ch = b.GetCharacter();
                    if (ch == EOF)
                    {
                        error = true;
                        return null;
                    }
                    else if (ch == Escape && !sawEscape)
                    {
                        sawEscape = true;
                    }
                    else if (sawEscape)  // to do: add && IsEscapedChar(ch)
                    {
                        sawEscape = false;
                        stringToken.Append(ch);
                    }
                    else if (ch == QuoteChar)
                    {
                        endOfString = true;
                    }
                    else
                    {
                        stringToken.Append(ch);
                    }
                }
                return new Token(Token.Kind.String, stringToken.ToString(), startPosition);
            }

            // Case 3: Integer
            else if (Char.IsDigit(ch) || (ch == Minus && !b.IsDelimited() && Char.IsDigit(b.Peek())))
            {
                StringBuilder intToken = new StringBuilder();
                intToken.Append(ch);

                while (!b.IsDelimited())
                {
                    ch = b.GetCharacter();
                    if (Char.IsDigit(ch))
                        intToken.Append(ch);
                    else
                    {
                        error = true;
                        return null;
                    }
                }
                return new Token(Token.Kind.Integer, intToken.ToString(), startPosition);
            }

            // Case 4: Function symbol
            else if (Char.IsLetterOrDigit(ch) || ch == AtSign)
            {
                StringBuilder symbolToken = new StringBuilder();
                symbolToken.Append(ch);

                while (!b.IsDelimited())
                {
                    ch = b.GetCharacter();
                    if (Char.IsLetterOrDigit(ch) || ch == Underscore)
                        symbolToken.Append(ch);
                    else
                    {
                        error = true;
                        return null;
                    }
                }

                string str = symbolToken.ToString();
                if (str == "true" || str == "false" || str == "True" || str == "False")
                    return new Token(Token.Kind.Boolean, str, startPosition);
                else if (str == "null")
                    return new Token(Token.Kind.Null, str, startPosition);
                else
                    return new Token(Token.Kind.Symbol, str, startPosition);
            }

            // Case 5: wildcard
            else if (ch == Underscore && b.IsDelimited())
            {
                return new Token(Token.Kind.Wildcard, new String(ch, 1), startPosition);
            }
            // Case 6: error
            else
            {
                error = true;
                return null;
            }
        }