I tried to generate a Let statement from the entire block of input for day 8. The function isValidExpression didn't find anything wrong with the expression but it returned a question mark when it was evaluated. The data viewer calculation dialog only allows 30,000 characters so I couldn't work with the full expression (54,000 characters) there. Reducing the size of the expression to several components allowed the expression to succeed so it seems as though the syntax was OK. In any case, there was very little to do to evaluate the code line by line.