private static string ConstructErrorMessage(ScannerErrorState error)
{
string errMsg = string.Empty;
switch (error)
{
case ScannerErrorState.CannotHaveBlankExponent:
errMsg = "Cannot have blank exponent";
break;
case ScannerErrorState.CannotHaveBlankMantissa:
errMsg = "Cannot have blank mantissa";
break;
case ScannerErrorState.InternalErrorCouldNotResolveTokenType:
errMsg = "Internal error could not resolve token type";
break;
case ScannerErrorState.InternalErrorCouldNotTransitionState:
errMsg = "Internal error could not transition scanner state";
break;
case ScannerErrorState.UnexpectedCharacter:
errMsg = "Unexpected character";
break;
case ScannerErrorState.UnexpectedSymbol:
errMsg = "Unexpected symbol";
break;
}
return(errMsg);
}
public ScannerException(ScannerErrorState error, int line, int startPos, int endPos)
: base(line, startPos, endPos, ConstructErrorMessage(error))
{
}
public Token GetNextToken()
{
StringBuilder tokenValue = new StringBuilder();
ScannerState scannerState = ScannerState.Start;
ScannerErrorState scannerError = ScannerErrorState.None;
bool finishedScan = false;
_startPosition = _pos;
while (!finishedScan)
{
bool ignoreCharacter = false;
char nextChar = GetNextRelevantChar();
#region DFA Implementation
switch (scannerState)
{
case ScannerState.Start:
if (char.IsWhiteSpace(nextChar))
{
scannerState = ScannerState.Start;
ignoreCharacter = true;
}
else if (char.IsLetter(nextChar))
{
scannerState = ScannerState.Identifier;
}
else if (char.IsDigit(nextChar))
{
scannerState = ScannerState.Number;
}
else if (IsSymbol(nextChar))
{
#region Scan symbol
switch (nextChar)
{
case '^':
scannerState = ScannerState.Power;
finishedScan = true;
break;
case '+':
scannerState = ScannerState.Plus;
finishedScan = true;
break;
case '-':
scannerState = ScannerState.Minus;
finishedScan = true;
break;
case '*':
scannerState = ScannerState.Multiplication;
finishedScan = true;
break;
case '/':
scannerState = ScannerState.Division;
finishedScan = true;
break;
case '[':
scannerState = ScannerState.OpenBracket;
finishedScan = true;
break;
case ']':
scannerState = ScannerState.CloseBracket;
finishedScan = true;
break;
case '(':
scannerState = ScannerState.OpenParenthesis;
finishedScan = true;
break;
case ')':
scannerState = ScannerState.CloseParenthesis;
finishedScan = true;
break;
case '{':
scannerState = ScannerState.BeginBracket;
finishedScan = true;
break;
case '}':
scannerState = ScannerState.EndBracket;
finishedScan = true;
break;
case '=':
scannerState = ScannerState.Assign;
break;
case '&':
scannerState = ScannerState.AlmostAnd;
break;
case '|':
scannerState = ScannerState.AlmostOr;
break;
case ',':
scannerState = ScannerState.Comma;
finishedScan = true;
break;
case '.':
scannerState = ScannerState.Dot;
finishedScan = true;
break;
case ';':
scannerState = ScannerState.SemiColon;
finishedScan = true;
break;
case '!':
scannerState = ScannerState.Not;
break;
case '<':
scannerState = ScannerState.LessThan;
break;
case '>':
scannerState = ScannerState.GreaterThan;
break;
case '%':
scannerState = ScannerState.Modulus;
finishedScan = true;
break;
default:
finishedScan = true;
scannerError = ScannerErrorState.UnexpectedSymbol;
RestoreChar(nextChar);
break;
}
#endregion
}
else if (nextChar == char.MaxValue)
{
scannerState = ScannerState.EndOfCode;
finishedScan = true;
}
else
{
finishedScan = true;
scannerError = ScannerErrorState.UnexpectedCharacter;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.Identifier:
if (char.IsLetterOrDigit(nextChar))
{
scannerState = ScannerState.Identifier;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.Number:
if (char.IsDigit(nextChar))
{
scannerState = ScannerState.Number;
}
else if (nextChar == '.')
{
scannerState = ScannerState.AlmostDecimal;
}
else if (nextChar == 'E')
{
scannerState = ScannerState.NumberWithExponent;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.AlmostDecimal:
if (char.IsDigit(nextChar))
{
scannerState = ScannerState.Decimal;
}
else
{
finishedScan = true;
scannerError = ScannerErrorState.CannotHaveBlankMantissa;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.Decimal:
if (char.IsDigit(nextChar))
{
scannerState = ScannerState.Decimal;
}
else if (nextChar == 'E')
{
scannerState = ScannerState.NumberWithExponent;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.NumberWithExponent:
if (char.IsDigit(nextChar))
{
scannerState = ScannerState.NumberWithUnsignedExponent;
}
else if (nextChar == '+')
{
scannerState = ScannerState.NumberWithSignedExponent;
}
else if (nextChar == '-')
{
scannerState = ScannerState.NumberWithSignedExponent;
}
else
{
finishedScan = true;
scannerError = ScannerErrorState.CannotHaveBlankExponent;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.NumberWithSignedExponent:
if (char.IsDigit(nextChar))
{
scannerState = ScannerState.NumberWithSignedExponent;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.NumberWithUnsignedExponent:
if (char.IsDigit(nextChar))
{
scannerState = ScannerState.NumberWithUnsignedExponent;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.Assign:
if (nextChar == '=')
{
scannerState = ScannerState.Equality;
finishedScan = true;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.Not:
if (nextChar == '=')
{
scannerState = ScannerState.Inequality;
finishedScan = true;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.LessThan:
if (nextChar == '=')
{
scannerState = ScannerState.LessThanEqualTo;
finishedScan = true;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.GreaterThan:
if (nextChar == '=')
{
scannerState = ScannerState.GreaterThanEqualTo;
finishedScan = true;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.AlmostOr:
if (nextChar == '|')
{
scannerState = ScannerState.Or;
finishedScan = true;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
case ScannerState.AlmostAnd:
if (nextChar == '&')
{
scannerState = ScannerState.And;
finishedScan = true;
}
else
{
finishedScan = true;
RestoreChar(nextChar);
ignoreCharacter = true;
}
break;
default:
scannerError = ScannerErrorState.InternalErrorCouldNotTransitionState;
break;
}
#endregion
if (scannerError != ScannerErrorState.None)
{
RestoreChar(nextChar);
ignoreCharacter = true;
throw new ScannerException(
scannerError,
_line,
_startPosition,
_pos
);
}
else
{
if (!ignoreCharacter)
{
tokenValue.Append(nextChar);
}
}
}
string tokenString = tokenValue.ToString();
Token token = new Token(
ResolveTokenType(scannerState, tokenString),
tokenString,
_line,
_startPosition,
!_haveRestoredChar ? _pos : _pos - 1
);
return(token);
}
