/// <summary>
/// Peek at the next available token without consuming it.
/// </summary>
/// <returns>the next available token, or the empty token if all tokens have been read</returns>
/// <see cref="Token.Empty"/>
public Token PeekToken()
{
if (_needToken)
{
_nextToken = ReadTokenFromReader();
_needToken = false;
}
return _nextToken;
}
/// <summary>
/// Handler for 1 or more construct
/// </summary>
/// <param name="separator">the separator token between items</param>
/// <param name="terminal">the ending token</param>
/// <param name="meth">the method to call to parse an item</param>
/// <param name="result">the parsed expression</param>
/// <param name="first">flag indicating whether this is the first item</param>
/// <returns>true if match parsed, false otherwise</returns>
private bool ReadAhead(Token separator, Token terminal, ExpressionMethod meth, out Expression result, ref bool first)
{
Token tok = PeekToken();
result = null;
if (tok == terminal)
{
ReadToken();
return false;
}
if (!first)
{
RequireToken(separator, tok, "Items should be separated by {0}", separator);
ReadToken();
}
else if (first && tok == separator)
throw new ParseException(string.Format("Error: unexpected token {0} at Line: {1}, Position: {2}", tok, tok.linenumber, tok.position));
result = meth();
first = false;
return true;
}
/// <summary>
/// Asserts that the token read is the one expected
/// </summary>
/// <param name="expected">the expected token</param>
/// <param name="actual">the actual token</param>
/// <param name="message">message to use in the exception if expected != actual</param>
private static void RequireToken(Token expected, Token actual, string message, params object[] args)
{
if (actual != expected)
{
message = string.Format(message, args);
throw new ParseException(message + " at Line: " + actual.linenumber + ", Position: " + actual.position + " Expected: " + expected + " got: " + actual);
}
}
/// <summary>
/// Test the token to see if its a quoted string
/// </summary>
/// <param name="tok">the token to test</param>
/// <returns>true if its a quoted string</returns>
private static bool IsQuotedString(Token tok)
{
return tok.type == TokenType.DoubleQuotedString || tok.type == TokenType.SingleQuotedString;
}
/// <summary>
/// Test the token to see if its a keyword
/// </summary>
/// <param name="tok">the token to test</param>
/// <returns>true if its a keyword</returns>
private static bool IsKeyword(Token tok)
{
// include null?
return tok.type == TokenType.Identifier && tok.value == "new";
}
/// <summary>
/// Test the token to see if its an identifier
/// </summary>
/// <param name="tok">the token to test</param>
/// <returns>true if its an identifier</returns>
private static bool IsIdentifier(Token tok)
{
return tok.type == TokenType.Identifier;
}
private bool Equals(Token other)
{
return type == other.type && value == other.value;
}