private static Nodes.ParseTreeNode CombineBinaryOperators(List<Nodes.ParseTreeNode> operands, List<Token> operators, IBinaryOperatorType operatorType, OperatorAssociativity associativity)
{
if (operators.Count + 1 != operands.Count)
{
throw new InvalidOperationException("You cannot combine binary operators if the number of operands is not equal to the number of operators plus one.");
}
// If there is just one operand, just return it.
if (operands.Count == 1)
{
return operands[0];
}
// If there are just two operands, all associativity rules are equivalent.
if (operands.Count == 2)
{
return new Nodes.BinaryOperatorNode
{
Left = operands[0],
Operator = operators[0],
OperatorType = operatorType,
Right = operands[1],
};
}
// If there are more than two operands and the operator is non-associative, throw a parse error.
if (associativity == OperatorAssociativity.NonAssociative)
{
throw new ParseException("The operator '" + operatorType.Name + "' is non-associative and therefore may not be used in groups of 3 or more without using parentheses for clarification.", operators[2].Span.Start);
}
// Otherwise, build up the tree with the proper associativity.
if (associativity == OperatorAssociativity.LeftAssociative)
{
Nodes.ParseTreeNode accumulator = null;
for (int i = 0; i < operands.Count; i++)
{
if (accumulator == null)
{
accumulator = operands[i];
}
else
{
var thenNode = new Nodes.BinaryOperatorNode
{
Left = accumulator,
Operator = operators[i - 1],
OperatorType = operatorType,
Right = operands[i],
};
accumulator = thenNode;
}
}
return accumulator;
}
else
{
Nodes.ParseTreeNode accumulator = null;
for (int i = operands.Count - 1; i >= 0; i--)
{
if (accumulator == null)
{
accumulator = operands[i];
}
else
{
var thenNode = new Nodes.BinaryOperatorNode
{
Left = operands[i],
Operator = operators[i],
OperatorType = operatorType,
Right = accumulator
};
accumulator = thenNode;
}
}
return accumulator;
}
}
public override ConstraintViolation VisitBinaryOperatorNode(BinaryOperatorNode binNode)
{
return null;
}
public abstract ConstraintViolation VisitBinaryOperatorNode(BinaryOperatorNode binNode);
