my base case the function should return a list of words but before returned a single word.
Very good decision. Now take a close look at how you phrased the second condition. According to the design recipe, it should be structured to match the second condition of your data definition for list-of-words. Does it? (define (insert-everywhere/in-single-word s w) (cond [(empty? w) (list s)] *[else (list (list s (first w)) (cons (first w) (insert-everywhere/in-single-word s (rest w))))]))* On Tue, Jul 6, 2010 at 3:14 PM, Sam Griff <sgrif...@gmail.com> wrote: > > Exercise 12.4.2 is notorius. When looking to (list 'a 'b 'c), you should > > exspect 6 distinct permutations. > > Jos > > Thanks for your response but that really doesn't help me much. I'm > focusing on insert-everywhere/in-single-word now. I understand what > arrangements does > and what permutations to expect. > > > My first suggestion is to check the function examples to make sure the > values they expect are consistent with your data definitions. > > Can you explain please? I'm not sure I fully understand. The only > thing I could see was in my base case the function should return a > list of words but before returned a single word. Is that what you > mean? > > (define (insert-everywhere/in-single-word s w) > (cond > [(empty? w) (cons (cons s empty) empty)] > [else ... (first w) ... (insert-everywhere/in-single-word s (rest w))])) > > > Amen. > > > > -- Make sure you truly understand list vs cons. If you have any doubts, > > stick to cons.-- For your template, spell out what each expression > produces > > before you finish the definition.-- Use the examples, especially the ones > > that fail.-- Figure out what you need to combine the pieces.-- Ideally, > > arrange the thing in a table: > > input | (first input) | .... | recursive result | expected result > > > > and keep adding examples until it clicks: i.e., until you know how to > > combine recursive result with some other things to get the expected > result. > > > > And do stick to the design recipe all the way down. > > Thanks! I will try those suggestions and see if they help. > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/users >
_________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
