private IFormulaOperator InterpretMinusToken(IFormulaToken previousToken, FormulaNodeSubtract minusToken)
{
// change from subtract to negative sign token
if (previousToken == null || previousToken is IFormulaOperator || previousToken is FormulaTokenParameterSeparator)
{
var negativeSignToken = FormulaTreeFactory.CreateNegativeSignNode(null);
SetOrigin(negativeSignToken, minusToken);
return negativeSignToken;
}
return minusToken;
}