private static IBoolable BuildExpression(List <Token> tokens)
{
// turn list of tokens into list of BoolExpressionElements
// they are in usual infix notation
// when this is done, their order is changed to Reverse Polish Notation
// meanwhile check, if it all can be represented as simple one negated IBoolable
// finally build BoolExpression
List <IBoolExpressionElement> infixList = new List <IBoolExpressionElement>();
List <Token> currentTokens = new List <Token>();
bool readingFunction = false;
Token previousToken = new Token(TokenType.Null);
// first, merge many tokens into fewer number of IBoolables
foreach (Token tok in tokens)
{
bool actionDone = false;
if (TokenGroups.IsLogicSign(tok.GetTokenType()))
{
if (readingFunction)
{
if (Brackets.AllBracketsClosed(currentTokens))
{
IBoolable ibo = BoolableBuilder.Build(currentTokens);
if (!ibo.IsNull())
{
infixList.Add(ibo);
}
else
{
return(null);
}
currentTokens.Clear();
readingFunction = false;
infixList.Add(new BoolExpressionOperator(GetBEOT(tok.GetTokenType())));
}
else
{
currentTokens.Add(tok);
}
}
else
{
if (currentTokens.Count > 0)
{
IBoolable ibo = BoolableBuilder.Build(currentTokens);
if (!ibo.IsNull())
{
infixList.Add(ibo);
}
else
{
return(null);
}
currentTokens.Clear();
}
infixList.Add(new BoolExpressionOperator(GetBEOT(tok.GetTokenType())));
}
actionDone = true;
}
if (tok.GetTokenType().Equals(TokenType.BracketOn))
{
if (readingFunction)
{
currentTokens.Add(tok);
}
else
{
if (currentTokens.Count == 1 && previousToken.GetTokenType().Equals(TokenType.Variable))
{
currentTokens.Add(tok);
readingFunction = true;
}
else
{
if (currentTokens.Count > 0)
{
IBoolable ibo = BoolableBuilder.Build(currentTokens);
if (!ibo.IsNull())
{
infixList.Add(ibo);
}
else
{
return(null);
}
currentTokens.Clear();
}
infixList.Add(new BoolExpressionOperator(BoolExpressionOperatorType.BracketOn));
}
}
actionDone = true;
}
if (tok.GetTokenType().Equals(TokenType.BracketOff))
{
if (readingFunction)
{
if (Brackets.AllBracketsClosed(currentTokens))
{
IBoolable ibo = BoolableBuilder.Build(currentTokens);
if (!ibo.IsNull())
{
infixList.Add(ibo);
}
else
{
return(null);
}
currentTokens.Clear();
readingFunction = false;
infixList.Add(new BoolExpressionOperator(BoolExpressionOperatorType.BracketOff));
}
else
{
currentTokens.Add(tok);
}
}
else
{
if (currentTokens.Count > 0)
{
IBoolable ibo = BoolableBuilder.Build(currentTokens);
if (!ibo.IsNull())
{
infixList.Add(ibo);
}
else
{
return(null);
}
currentTokens.Clear();
}
infixList.Add(new BoolExpressionOperator(BoolExpressionOperatorType.BracketOff));
}
actionDone = true;
}
if (!actionDone)
{
currentTokens.Add(tok);
}
previousToken = tok;
}
if (currentTokens.Count > 0)
{
IBoolable ibo = BoolableBuilder.Build(currentTokens);
if (!ibo.IsNull())
{
infixList.Add(ibo);
}
else
{
return(null);
}
}
// try to build negation of one boolable
if (infixList.Count == 2 && (infixList[0] is BoolExpressionOperator) && (infixList[1] is IBoolable) &&
(infixList[0] as BoolExpressionOperator).GetOperatorType().Equals(BoolExpressionOperatorType.Not))
{
return(new NegatedBoolable(infixList[1] as IBoolable));
}
// check if value of infixlist can be computed (check order of elements)
if (!CheckExpressionComputability(infixList))
{
throw new SyntaxErrorException("ERROR! Wrong syntax of logic expression.");
}
// if everything is right, finally build BoolExpression in RPN
return(new BoolExpression(ReversePolishNotation(infixList)));
}