private IToken ScanNumber(int start)
{
bool ParsingFraction = false;
while (Advancable())
{
if (CurrentCharacter.IsNumeric())
{
continue;
}
else if (CurrentCharacter.IsWhiteSpace())
{
return(Add(EToken.Number, start, this));
}
else if (CurrentCharacter != '.')
{
return(Add(EToken.Number, start, Formula.Substring(start - 1, CharPosition-- - start)));
}
else if (ParsingFraction)
{
return(Add(EToken.ScanError, start, this));
}
else
{
ParsingFraction = true;
}
}
return(Add(EToken.Number, start, this));
}
private IToken ScanIdent(int start, Func <char, bool> extraChars)
{
while (Advancable())
{
if (CurrentCharacter.IsAlphanumeric() || extraChars(CurrentCharacter))
{
continue;
}
else if (CurrentCharacter.IsWhiteSpace())
{
return(Add(EToken.Identifier, start, this));
}
else
{
return(Add(EToken.Identifier, start, Formula.Substring(start - 1, CharPosition-- - start)));
}
}
return(Add(EToken.Identifier, start, this));
}
private IToken ScanStringLiteral(int start)
{
while (Advancable())
{
if (CurrentCharacter == '"')
{
if (!Advancable() || CurrentCharacter.IsWhiteSpace())
{
return(Add(EToken.StringLiteral, start, this));
}
else if (CurrentCharacter == '"')
{
continue;
}
else
{
return(Add(EToken.StringLiteral, start, Formula.Substring(start - 1, CharPosition-- - start)));
}
}
}
return(Add(EToken.ScanError, start, this));
}
public IToken Scan()
{
if (CharPosition == 1 && CurrentCharacter == '\'')
{
return(Add(EToken.StringLiteral, 1, Formula));
}
while (Advancable())
{
if (!CurrentCharacter.IsWhiteSpace())
{
var start = CharPosition;
switch (CurrentCharacter)
{
case '!': return(Add(EToken.Bang, start, GetText(start)));
case '=': return(Add(EToken.EqualsOperator, start, GetText(start)));
case ',': return(Add(EToken.Comma, start, GetText(start)));
case ';': return(Add(EToken.Semicolon, start, GetText(start)));
case '+':
case '-':
case '%': return(Add(EToken.UnaryOperator, start, GetText(start)));
case '*':
case '/':
case '&':
case '^': return(Add(EToken.BinaryOperator, start, GetText(start)));
case '<':
case '>': if (IsEOT)
{
break;
}
if (NextCharacterIs('='))
{
CharPosition++;
}
return(Add(EToken.BinaryOperator, start, GetText(start)));
case '(': ParenDepth++; return(Add(EToken.OpenParen, start, GetText(start)));
case ')': ParenDepth--; return(Add(EToken.CloseParen, start, GetText(start)));
case '{': BraceDepth++; return(Add(EToken.OpenBrace, start, GetText(start)));
case '}': BraceDepth--; return(Add(EToken.CloseBrace, start, GetText(start)));
case '#': return(ScanErrorIdent(start));
case '"': return(ScanStringLiteral(start));
case '\'': return(ScanClosedExternalRef(start));
case '[': return(ScanOpenExternalRef(start));
default:
if (CurrentCharacter.IsNumeric())
{
return(ScanNumber(start));
}
if (CurrentCharacter.IsAlpha())
{
return(ScanIdentifier(start));
}
return(Add(EToken.ScanError, start, this));
}
}
}
return(IsEOT ? Add(EToken.EOT, CharPosition, this)
: Add(EToken.ScanError, CharPosition, this));
}
