Hey there, I'm just getting started with Lisp/Scheme/Racket and going through HTDP. I'm loving it and learning much along the way. Thank you Matthias, Robert, Matthew, and Shriram for everything you've done here.
Anyways I have a question about exercise 9.5.4; the problem statement being: "Develop the function check-range1?, which consumes a list of temperature measurements (represented as numbers) and checks whether all measurements are between 5*C and 95*C." I have managed to create a working solution as follows: ;; check-range1? : list-of-numbers -> boolean ;; checks whether temperatures in a-list-of-temperatures are between 5*C and 95*C ;; examples: ;; ... ;; ... ;; ... ;; body: (define (check-range1? a-list-of-temperatures) (cond ((empty? a-list-of-temperatures) true) (else (and (and (> (first a-list-of-temperatures) 5) (> 95 (first a-list-of-temperatures))) (check-range1? (rest a-list-of-temperatures)))))) Everything works as it should, except when testing the program against an empty list...it returns true, naturally. However, logically I feel that an empty list should produce false, as it doesn't contain any temperatures between 5*C and 95*C. Am I thinking incorrectly and the program is fine? Or is this logic correct and the program is wrong? I know that if I were to change ((empty? a-list-of-temperatures) true) to ((empty? a-list-of-temperatures) false) then an empty list would produce false, but so would all results as false would recursively traverse the list. Any thoughts will be greatly appreciated! -- hakkum _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
