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 <[email protected]> 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 <[email protected]> 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 <[email protected]> >> 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 <[email protected]> >> 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 [email protected]. >> >>> 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 [email protected]. >> > 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 [email protected]. >> 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
