The goal of this is to check if the character taken into account is a number or operand and then output it into a list which will be written out to a txt file. I'm wondering which process would be more efficient, whether to do it as I stated above (writing it to a list and then writing that list out into a file) or being writing out into a txt file right from the procedure. I'm new with scheme so I apologize if I am not using the correct terminology (define input '("3" "+" "4")) (define check (if (number? (car input)) (write this out to a list or directly to a file) (check the rest of file))) Another question I had in mind, how can I make it so that the check process is recursive? I know it's a lot of asking but I've getting a little frustrated with checking out the methods that I have found on other sites. I really appreciate the help!