private bool ExpectIdentifier(string name, out Token token)
{
return ExpectToken(
TokenType.Identifier,
(value) =>
{
return value.Equals(name, StringComparison.OrdinalIgnoreCase);
},
out token);
}
private bool ExpectToken(TokenType type, Func<string, bool> tokenPredicate, out Token token)
{
token = null;
Token testToken = mLexer.Peek();
if (testToken.Type == type && tokenPredicate(testToken.Value))
{
token = mLexer.Next();
}
return (token != null);
}
// Used by the parser to read and consume the next token
public Token Next()
{
// If the next token has already been Peek()'d, return it
if (mNext != null)
{
Token next = mNext;
mNext = null;
return next;
}
if (mCurrentPosition >= mInput.Length)
{
// Already parsed entire input string
return Token.EndOfFile();
}
char c = mInput[mCurrentPosition];
if (Char.IsWhiteSpace(c))
{
return Token.Whitespace(ReadSimpleToken(Char.IsWhiteSpace));
}
else if (Char.IsLetter(c))
{
return Token.Identifier(ReadSimpleToken(Char.IsLetterOrDigit));
}
else if (Char.IsDigit(c))
{
return Token.Number(ReadSimpleToken(Char.IsDigit));
}
else if (IsQuoteChar(c))
{
return Token.String(ReadString(c));
}
else if (!Char.IsControl(c))
{
// Anything that fell through the above checks, and that is not a control character
// is something we'll try to treat as a symbol
string symbol = ReadSymbol();
if (!string.IsNullOrEmpty(symbol))
{
return Token.Symbol(symbol);
}
}
// Failed to match a token
return Token.Error(mInput, mCurrentPosition);
}
// Used by the parser to look at the next token, without consuming it
public Token Peek()
{
// Implement peek by using a cache value for the next token
if (mNext == null)
{
mNext = Next();
}
return mNext;
}
private bool ExpectToken(TokenType type, out Token token)
{
token = null;
Token testToken = mLexer.Peek();
if (testToken.Type == type)
{
token = mLexer.Next();
}
return (token != null);
}
private bool ExpectString(out Token token)
{
return ExpectToken(TokenType.String, out token);
}
private bool ExpectNumber(out Token token)
{
return ExpectToken(TokenType.Number, out token);
}