// This is a very simple parser, that only verifies if the input is correct.
//
public bool ParseExpression(string input)
{
var tokenStream = _tokenizer.CreateTokenStream(input);
if (tokenStream.Peek().TokenType != EExpressionTokenType.Digit &&
tokenStream.Peek().TokenType != EExpressionTokenType.ParenthesesOpen &&
tokenStream.Peek().TokenType != EExpressionTokenType.End)
{
throw new ParseException(EExceptionReason.StartExpressionError, tokenStream.Peek().StartIndex);
}
int parenthesesCounter = 0;
while (tokenStream.IsFinshed == false)
{
var token = tokenStream.Next();
switch (token.TokenType)
{
case EExpressionTokenType.ParenthesesOpen: // next token must be a digit or another paranthesis open
parenthesesCounter++;
{
var peeked = tokenStream.Peek();
if (peeked.TokenType != EExpressionTokenType.Digit && peeked.TokenType != EExpressionTokenType.ParenthesesOpen)
{
throw new ParseException(EExceptionReason.StartExpressionError, token.Data, token.StartIndex);
}
}
break;
case EExpressionTokenType.ParenthesesClose: // next token must be an operator or end or paranthesis close
parenthesesCounter--;
if (parenthesesCounter < 0)
{
throw new ParseException(EExceptionReason.UnmatchedError, token.Data, token.StartIndex); // unmatched )
}
{
var peeked = tokenStream.Peek();
if (peeked.TokenType != EExpressionTokenType.Div && peeked.TokenType != EExpressionTokenType.Mult &&
peeked.TokenType != EExpressionTokenType.Add && peeked.TokenType != EExpressionTokenType.Sub &&
peeked.TokenType != EExpressionTokenType.End && peeked.TokenType != EExpressionTokenType.ParenthesesClose)
{
throw new InvalidTokenException(peeked.Data, token.StartIndex, token.Data);
}
}
break;
case EExpressionTokenType.Digit: // next token must be parantheses close or an operation or end
{
var peeked = tokenStream.Peek();
if (peeked.TokenType != EExpressionTokenType.Add &&
peeked.TokenType != EExpressionTokenType.Sub &&
peeked.TokenType != EExpressionTokenType.Mult &&
peeked.TokenType != EExpressionTokenType.Div &&
peeked.TokenType != EExpressionTokenType.ParenthesesClose &&
peeked.TokenType != EExpressionTokenType.End)
{
throw new InvalidTokenException(peeked.Data, token.StartIndex, token.Data);
}
}
break;
case EExpressionTokenType.Add: // next token must be parantheses or digit
case EExpressionTokenType.Sub:
case EExpressionTokenType.Mult:
case EExpressionTokenType.Div:
{
var peeked = tokenStream.Peek();
if (
peeked.TokenType != EExpressionTokenType.ParenthesesOpen &&
peeked.TokenType != EExpressionTokenType.Digit)
{
throw new ParseException(EExceptionReason.UnmatchedError, token.Data, token.StartIndex);
}
}
break;
}
}
if (parenthesesCounter != 0)
{
throw new ParseException(EExceptionReason.UnmatchedError, "(", input.Length); // unclosed parantheses
}
return(true);
}
// This is a very simple parser, that only verifies if the input is correct.
//
public bool ParseExpression(string input)
{
var tokenStream = _tokenizer.CreateTokenStream(input);
if (tokenStream.Peek().TokenType != EExpressionTokenType.Digit &&
tokenStream.Peek().TokenType != EExpressionTokenType.ParenthesesOpen &&
tokenStream.Peek().TokenType != EExpressionTokenType.End)
{
var peeked = tokenStream.Peek();
throw new ParseException(String.Format("Parser error at position {0}: An expression must start with a digit or \"(\"", peeked.StartIndex + 1)); // unmatched )
}
while (tokenStream.IsFinshed == false)
{
var token = tokenStream.Next();
switch (token.TokenType)
{
case EExpressionTokenType.ParenthesesOpen: // next token must be a digit or another paranthesis open
_parenthesesCounter++;
{
var peeked = tokenStream.Peek();
if (peeked.TokenType != EExpressionTokenType.Digit && peeked.TokenType != EExpressionTokenType.ParenthesesOpen)
{
throw new Exception();
}
}
break;
case EExpressionTokenType.ParenthesesClose: // next token must be an operator or end or paranthesis close
_parenthesesCounter--;
if (_parenthesesCounter < 0)
{
int countClosingParethesis = input.Count(f => f == ')');
int countOpeneninggParethesis = input.Count(f => f == '(');
if (countClosingParethesis != countOpeneninggParethesis)
{
int i = 1;
var peeked = tokenStream.Peek();
string s = input[peeked.StartIndex - i].ToString();
while (s.Equals(" "))
{
s = input[peeked.StartIndex - ++i].ToString();
}
throw new ParseException(String.Format("Parser error at position {0}: unmatched \")\" in expression", peeked.StartIndex - 1)); // unmatched )
}
//int i = 1;
//var peeked = tokenStream.Peek();
//string s = input[peeked.StartIndex - i].ToString();
//while (s.Equals(" "))
//{
// s = input[peeked.StartIndex - ++i].ToString();
//}
//throw new ParseException(String.Format("Unexpected input after \"{0}\" at position {1}: expected \")\",\"+\",\"-\",\"*\",\"\\\" or end of expression but found \"(\". ", s, peeked.StartIndex));
}
{
var peeked = tokenStream.Peek();
if (peeked.TokenType != EExpressionTokenType.Div && peeked.TokenType != EExpressionTokenType.Mult &&
peeked.TokenType != EExpressionTokenType.Add && peeked.TokenType != EExpressionTokenType.Sub &&
peeked.TokenType != EExpressionTokenType.End && peeked.TokenType != EExpressionTokenType.ParenthesesClose)
{
peeked = tokenStream.Peek();
throw new ParseException(String.Format("Parser error at position {0}: unmatched \")\" in expression", peeked.StartIndex)); // unmatched )
}
}
break;
case EExpressionTokenType.Digit: // next token must be parantheses close or an operation or end
{
var peeked = tokenStream.Peek();
if (peeked.TokenType != EExpressionTokenType.Add &&
peeked.TokenType != EExpressionTokenType.Sub &&
peeked.TokenType != EExpressionTokenType.Mult &&
peeked.TokenType != EExpressionTokenType.Div &&
peeked.TokenType != EExpressionTokenType.ParenthesesClose &&
peeked.TokenType != EExpressionTokenType.End)
{
int i = 1;
string s = input[peeked.StartIndex - i].ToString();
while (s.Equals(" "))
{
s = input[peeked.StartIndex - ++i].ToString();
}
throw new ParseException(String.Format("Unexpected input after \"{0}\" at position {1}: expected \")\",\"+\",\"-\",\"*\",\"\\\" or end of expression but found \"(\". ", s, peeked.StartIndex));
}
}
break;
case EExpressionTokenType.Add: // next token must be parantheses or digit
case EExpressionTokenType.Sub:
case EExpressionTokenType.Mult:
case EExpressionTokenType.Div:
{
var peeked = tokenStream.Peek();
if (
peeked.TokenType != EExpressionTokenType.ParenthesesOpen &&
peeked.TokenType != EExpressionTokenType.Digit)
{
throw new Exception();
}
}
break;
}
}
if (_parenthesesCounter != 0)
{
int countClosingParethesis = input.Count(f => f == ')');
int countOpeneninggParethesis = input.Count(f => f == '(');
if (countClosingParethesis != countOpeneninggParethesis)
{
throw new ParseException(String.Format("Parser error at position {0}: unmatched \"(\" in expression", input.Length)); // unclosed parantheses
}
}
return(true);
}
