private static IArithExpression ParseExpression(Token start, Func <Token, bool> endOfExpression, TokenCursor tokens, bool moveToPrevAtEnd)
{
var current = start;
IArithExpression resultExpr = null;
//while next && end(next).not()
while (current.IsNotNull())
{
resultExpr = ParseToken(current, resultExpr, tokens);
current = tokens.Next();
if (current.IsNotNull() && endOfExpression(current))
{
if (moveToPrevAtEnd)
{
tokens.MovePrev();
}
break;
}
}
return(resultExpr);
//operators precedence:
//- test for multiplicative operator - build one first
//- test for expression group - (....)
//- test for function call - ID(args)
//prevExpression is not applicable in case of ROperand parsing
}
private MultiplicativeOperatorExpression(IArithExpression lOperand, IArithExpression rOperand, bool isDivision) : base(lOperand, rOperand)
{
if (LOperand == null)
{
throw new ParsingException("LOperand is required");
}
IsDivision = isDivision;
}
protected OperatorExpression(IArithExpression lOperand, IArithExpression rOperand)
{
if (rOperand == null)
{
throw new ParsingException("ROperand is required");
}
LOperand = lOperand;
ROperand = rOperand;
}
public static OperatorExpression Create(string op, IArithExpression lOperand, IArithExpression rOperand)
{
switch (op)
{
case "+":
return(AdditiveOperatorExpression.Addition(lOperand, rOperand));
case "-":
return(AdditiveOperatorExpression.Subtraction(lOperand, rOperand));
case "*":
return(MultiplicativeOperatorExpression.Multiplication(lOperand, rOperand));
case "/":
return(MultiplicativeOperatorExpression.Division(lOperand, rOperand));
default:
throw new ParsingException("Unexpected operator " + op);
}
}
private static IArithExpression ParseToken(Token token, IArithExpression prevExpr, TokenCursor tokens)
{
switch (token.Type)
{
case TokenType.Value:
return(ParseValue(token));
case TokenType.AdditiveOperator:
case TokenType.MultiplicativeOperator:
return(ParseOperator(token, prevExpr, tokens));
case TokenType.OParenthesis:
return(ParseGroup(tokens.Next(), tokens));
case TokenType.CParenthesis:
return(prevExpr);
default:
throw new ParsingException("Unexpected token: " + token);
}
}
public static MultiplicativeOperatorExpression Division(IArithExpression lOperand, IArithExpression rOperand)
{
return(new MultiplicativeOperatorExpression(lOperand, rOperand, true));
}
private static IArithExpression ParseOperator(Token operatorToken, IArithExpression lOperand, TokenCursor tokens)
{
var rOperand = ParseRightOperand(tokens.Next(), operatorToken, tokens);
return(OperatorExpression.Create(operatorToken.Value, lOperand, rOperand));
}
public static AdditiveOperatorExpression Subtraction(IArithExpression lOperand, IArithExpression rOperand)
{
return(new AdditiveOperatorExpression(lOperand, rOperand, true));
}
public static AdditiveOperatorExpression Addition(IArithExpression lOperand, IArithExpression rOperand)
{
return(new AdditiveOperatorExpression(lOperand, rOperand, false));
}
private AdditiveOperatorExpression(IArithExpression lOperand, IArithExpression rOperand, bool isSubtraction) : base(lOperand, rOperand)
{
IsSubtraction = isSubtraction;
}
