Just realized that your list was sorted ascending, but for some reason, I latched into 'descending'. In the text below where I said 'smaller' it should say 'bigger'.
"...put a number (x) on the front of a list if (first lst) is BIGGER than x. If (first lst) is not BIGGER..." On Sun, Nov 27, 2016 at 3:13 PM, David Storrs <david.sto...@gmail.com> wrote: > Ben, I'm guessing that this is homework? Unless you have an artificial > constraint stopping it, I would suggest that you take a look at the docs > for Racket's built-in 'sort' function. Also, 'cons'. (See the 'Pairs and > Lists' documentation.) > > As a more general hint, Racket is a functional language with a strong > grounding in recursion. The way recursion works (pardon me if you already > know this, but I'm building to a point) is that you have a function which > can do two things: solve a very trivial problem, or call itself again in > order to get one step closer to that trivial problem. The standard example > is the factorial function: > > (define (factorial n) > (cond [(= n 1) 1] > [else n * (factorial (- n 1))])) > > This function knows how to solve a trivial problem: find the factorial of > 1. If it's given a number other than 1 then it moves one step closer > towards the problem that it knows how to solve, building up its result on > the stack. > > The two procedures you want to write would be good candidates for > recursive solutions. > > The first procedure you've already written. It knows how to solve a > trivial problem: put a number (x) on the front of a list if (first lst) is > smaller than x. If (first lst) is not smaller, then it should do whatever > is necessary to get one step closer to its result. > > The second procedure I don't want to outline too clearly, so I will ask: > what is the definition of a sorted list? How do you sort lists of 0, 1, 2, > and 3 elements? If you can answer those questions then you'll have your > solution. (I suggest answering them in the order I asked them.) > > Good luck! > > Dave > > On Sun, Nov 27, 2016 at 1:31 PM, Jon Zeppieri <zeppi...@gmail.com> wrote: > >> The first question is: what is a list? Forget empty lists for a moment. >> Think about a list with a single real in it. According to your program, >> what does that look like? >> >> You're defining lists in terms of pairs. Okay, so let's say you want a >> list, where the only element in it is the number 1.0. What does that look >> like, in terms of pairs. Maybe you have a pair where the "first" field >> contains 1.0. But what does the "rest" field contain? What is the *rest* of >> a list that only has one thing in it? >> >> >> >> >> > On Nov 27, 2016, at 4:23 PM, Ben Ghanem Anis <ansebio2...@gmail.com> >> wrote: >> > >> >> On Sunday, November 27, 2016 at 10:16:34 PM UTC+1, Jon Zeppieri wrote: >> >> Well, okay, first your program needs to admit the possibility of an >> empty list. But once it does, see my previous message. >> >> >> >>> On Nov 27, 2016, at 3:45 PM, Ben Ghanem Anis <ansebio2...@gmail.com> >> wrote: >> >>> >> >>> Hey guys, >> >>> I need some help .. >> >>> I need to write two procedures .. first one should be able to insert >> a real number in the right position in a list (that is by default sorted >> ascending) made of pairs (make-pair), also i need to use the procedure to >> write another one that is able to sort in an ascending way a whole list of >> real numbers. >> >>> I already did the first step(see included shot) .. but i'm really >> stuck >> >>> Help! >> >>> >> >>> -- >> >>> You received this message because you are subscribed to the Google >> Groups "Racket Users" group. >> >>> To unsubscribe from this group and stop receiving emails from it, >> send an email to racket-users+unsubscr...@googlegroups.com. >> >>> For more options, visit https://groups.google.com/d/optout. >> >>> <Untitled.jpg> >> > And how could i make it accept empty lists ? >> > >> > -- >> > You received this message because you are subscribed to the Google >> Groups "Racket Users" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> an email to racket-users+unsubscr...@googlegroups.com. >> > For more options, visit https://groups.google.com/d/optout. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
