/// <summary>
/// Skip through a block comment.
/// </summary>
private void SkipBlockComment()
{
// Stop when (Peek == * && PeekNext == /) ---> (Peek != * || PeekNext != /)
// Keep moving through the comment until it reaches */
while ((Peek() != '*' || PeekNext() != '/') && IsAtEnd() == false)
{
// Allow multi-line block comments
if (Peek() == '\n')
{
line++;
}
Advance();
}
// Unterminated comment
if (IsAtEnd())
{
Min.Error(line, "Unterminated block comment.");
return;
}
// Move past the closing comment */
Advance();
Advance();
}
/// <summary>
/// Read a full string between quotes " and add it as a token.
/// </summary>
private void ReadString()
{
// Keep moving through the string until it reaches "
while (Peek() != '"' && IsAtEnd() == false)
{
// Allow multi-line strings
if (Peek() == '\n')
{
line++;
}
Advance();
}
// Unterminated string
if (IsAtEnd())
{
Min.Error(line, "Unterminated string.");
return;
}
// Move past the closing quote (")
Advance();
// Trim the surrounding quotes
string value = source.Substring(start + 1, current - 2 - start);
// TODO: Support escape sequences (unescape them here)
AddToken(TokenType.STRING, value);
}
/// <summary>
/// Report a Parsing Error at a specific token.
/// </summary>
/// <param name="token">The token that encountered an error.</param>
/// <param name="message">The message of the error.</param>
/// <returns>The Parsing Error created as a result.</returns>
private ParseError Error(Token token, string message)
{
Min.Error(token, message);
return(new ParseError());
}
/// <summary>
/// Move through the characters to scan one token and add it to the list of tokens.
/// </summary>
private void ScanToken()
{
char c = Advance();
switch (c)
{
case '(': AddToken(TokenType.LEFT_PAREN); break;
case ')': AddToken(TokenType.RIGHT_PAREN); break;
case '{': AddToken(TokenType.LEFT_BRACE); break;
case '}': AddToken(TokenType.RIGHT_BRACE); break;
case ',': AddToken(TokenType.COMMA); break;
case '.': AddToken(TokenType.DOT); break;
case ';': AddToken(TokenType.SEMICOLON); break;
case '+': AddToken(TokenType.PLUS); break;
case '-': AddToken(TokenType.MINUS); break;
case '*': AddToken(TokenType.STAR); break;
case '?': AddToken(TokenType.QUESTION); break;
case ':': AddToken(TokenType.COLON); break;
case '!': AddToken(Match('=') ? TokenType.BANG_EQUAL : TokenType.BANG); break;
case '=': AddToken(Match('=') ? TokenType.EQUAL_EQUAL : TokenType.EQUAL); break;
case '<': AddToken(Match('=') ? TokenType.LESS_EQUAL : TokenType.LESS); break;
case '>': AddToken(Match('=') ? TokenType.GREATER_EQUAL : TokenType.GREATER); break;
case '&':
if (Match('&'))
{
AddToken(TokenType.AND);
}
else
{
// TODO: Bitwise "&" does not exist yet.
Min.Error(line, $"Unexpected character \"{c}\"");
}
break;
case '|':
if (Match('|'))
{
AddToken(TokenType.OR);
}
else
{
// TODO: Bitwise "|" does not exist yet.
Min.Error(line, $"Unexpected character \"{c}\"");
}
break;
case '/':
// Comment //
if (Match('/'))
{
// A comment goes until the end of the line, keep consuming characters until then.
while (Peek() != '\n' && IsAtEnd() == false)
{
Advance();
}
}
// Block comment /*
else if (Match('*'))
{
SkipBlockComment();
}
// Any other slash /
else
{
AddToken(TokenType.SLASH);
}
break;
case '"':
ReadString();
break;
case ' ':
case '\r':
case '\t':
// Ignore whitespace
break;
case '\n':
line++;
break;
default:
// Have to go through default because bools/methods don't work in switch/case
if (IsDigit(c))
{
ReadNumber();
}
else if (IsAlpha(c))
{
ReadIdentifier();
}
else
{
Min.Error(line, $"Unexpected character \"{c}\"");
}
break;
}
}