public ExpressionizeResult GenerateExpression()
{
ExpressionizeResult result = CreateExpression(MinOperatorPrecedence);
if (currentToken != null && currentToken.Type == TokenType.ParenRight)
{
return(ExpressionizeResult.NewError(ErrorInfo.UnexpectRightParen));
}
return(result);
}
ExpressionizeResult CreateExpression(int basePrecedence)
{
Expression single = null;
// Make an atom.
ExpressionizeResult atomResult = CreateAtom();
if (!atomResult.Success)
{
return(atomResult);
}
// Atomizing succeeded.
single = atomResult.CalculatedExpression;
while (true)
{
// After an atom might be an operator, an argument or another expression.
// End of the token list.
if (currentToken == null)
{
break;
}
// Operator after an atom.
if (TokenType.Operator.HasFlag(currentToken.Type))
{
BinaryType binaryType = currentToken.Type.ToBinaryType();
int opPrecedence = binaryType.GetPrecedence();
if (opPrecedence < basePrecedence)
{
break;
}
int nextPrecedence = binaryType.IsLeftAssociative() ? (opPrecedence + 1) : opPrecedence;
GetNextToken();
ExpressionizeResult rightResult = CreateExpression(nextPrecedence);
if (!rightResult.Success)
{
return(rightResult);
}
Expression left = single;
Expression right = rightResult.CalculatedExpression;
single = new BinaryExpression(left, right, binaryType);
}
else
{
// Variable or left parenthesis after an atom,
// connect them with implied multiplication.
if (currentToken.Type == TokenType.Variable || currentToken.Type == TokenType.ParenLeft)
{
BinaryType binaryType = BinaryType.ImpliedMultiply;
int opPrecedence = binaryType.GetPrecedence();
if (opPrecedence < basePrecedence)
{
break;
}
int nextPrecedence = binaryType.IsLeftAssociative() ? (opPrecedence + 1) : opPrecedence;
// No need to consume the operator token.
ExpressionizeResult rightResult = CreateExpression(nextPrecedence);
if (!rightResult.Success)
{
return(rightResult);
}
Expression right = rightResult.CalculatedExpression;
single = new BinaryExpression(single, right, binaryType);
}
else
{
if (currentToken.Type == TokenType.Constant)
{
return(ExpressionizeResult.NewError(ErrorInfo.ExpectOperator));
}
// The current expression ends if we encounter anything else.
break;
}
}
}
return(ExpressionizeResult.NewSuccess(single));
}
ExpressionizeResult CreateAtom()
{
if (currentToken == null)
{
return(ExpressionizeResult.NewError(ErrorInfo.ExpectExpression));
}
if (currentToken.Type == TokenType.Constant)
{
Constant constant = (Constant)currentToken;
GetNextToken();
// Create a new constant expression.
ConstantExpression constantExpression = new ConstantExpression(constant.Value);
return(ExpressionizeResult.NewSuccess(constantExpression));
}
else if (currentToken.Type == TokenType.Variable)
{
Variable variable = (Variable)currentToken;
GetNextToken();
// Create a new argument expression.
VariableExpression argumentExpression = new VariableExpression(variable.Name);
return(ExpressionizeResult.NewSuccess(argumentExpression));
}
else if (TokenType.UnaryOperator.HasFlag(currentToken.Type))
{
UnaryType unaryType = currentToken.Type.ToUnaryType();
GetNextToken();
// Since unary operator is left associative, we add 1 to the base precedence.
ExpressionizeResult childResult = CreateExpression(unaryType.GetPrecedence() + 1);
if (!childResult.Success)
{
return(childResult);
}
Expression childExpression = childResult.CalculatedExpression;
// Create a new unary expression.
UnaryExpression unaryExpression = new UnaryExpression(childExpression, unaryType);
return(ExpressionizeResult.NewSuccess(unaryExpression));
}
else if (currentToken.Type == TokenType.ParenLeft)
{
GetNextToken();
// Try to make a sub-expression enclosed by this left parenthesis.
ExpressionizeResult subResult = CreateExpression(MinOperatorPrecedence);
if (!subResult.Success)
{
return(subResult);
}
Expression subExpression = subResult.CalculatedExpression;
// Expect a matching right parenthesis.
if (currentToken != null && currentToken.Type == TokenType.ParenRight)
{
GetNextToken();
return(ExpressionizeResult.NewSuccess(subExpression));
}
else
{
return(ExpressionizeResult.NewError(ErrorInfo.ExpectRightParen));
}
}
else if (currentToken.Type == TokenType.Function)
{
// A function has two parts:
// - An identifier(name)
// - Its arguments enclosed in a pair of parens.
FunctionHeader functionHeader = (FunctionHeader)currentToken;
List <Expression> argumentsList = new List <Expression>();
GetNextToken();
if (currentToken != null && currentToken.Type == TokenType.ParenLeft)
{
GetNextToken();
// Only create expressions for each argument if the function requires any.
if (functionHeader.ArgumentCount > 0)
{
// NOTE: Handle multiple args here.
ExpressionizeResult argumentResult = CreateExpression(MinOperatorPrecedence);
if (!argumentResult.Success)
{
return(argumentResult);
}
argumentsList.Add(argumentResult.CalculatedExpression);
}
if (currentToken != null && currentToken.Type == TokenType.ParenRight)
{
GetNextToken();
// Create a function expression.
FunctionExpression functionExpression =
new FunctionExpression(
functionHeader.Name,
functionHeader.Target,
argumentsList);
return(ExpressionizeResult.NewSuccess(functionExpression));
}
else
{
return(ExpressionizeResult.NewError(ErrorInfo.ExpectRightParen));
}
}
else
{
return(ExpressionizeResult.NewError(ErrorInfo.ExpectLeftParen));
}
}
return(ExpressionizeResult.NewError(ErrorInfo.ExpectExpression));
}
