You may wish to read up on the design recipe and the necessity of ‘local’ definitions in HtDP2e:
http://www.ccs.neu.edu/home/matthias/HtDP2e/ > On Feb 13, 2017, at 3:46 PM, Angus Comber <[email protected]> wrote: > > But it has to have the signature maxval lst - it is a homework problem. > > So I thought I would need max in the helper function. Basically to keep an > internal max saved value. Is there another way? > > On 13 February 2017 at 20:38, Matthias Felleisen <[email protected]> wrote: > > Just lift aux out. > > > > On Feb 13, 2017, at 3:18 PM, Angus Comber <[email protected]> wrote: > > > > If I change the code to: > > > > (define (maxval lst) > > (define (aux lst max) > > (cond [(null? lst) max] > > [(> (car lst) max) (aux (cdr lst) (car lst))] > > [#t (aux (cdr lst) max)])) > > (aux lst 0)) > > > > and comment out #lang racket at the top of the file and select Beginning > > Student as the language then I get error: > > > > define: expected only one expression for the function body, but found 1 > > extra part > > > > Is this because there is a 2nd define in the function? Or do I need some > > syntax to indicate to run aux at the end of the definition. > > > > On 12 February 2017 at 21:34, Matthias Felleisen <[email protected]> > > wrote: > > > > > On Feb 12, 2017, at 3:00 PM, Angus <[email protected]> wrote: > > > > > > I am a beginner Racket developer by the way. > > > > > > Here is my maxval function which is supposed to take a list and return > > > the largest integer in the list. > > > > > > (define (maxval lst) > > > (define (aux lst max) > > > (cond [(null? lst) max] > > > [(car lst) > max (aux (cdr lst) (car lst))] > > > [#t (aux (cdr lst) max)])) > > > (aux lst 0)) > > > > > > > > > Using the function always returns the last value in the list > > > > > >> (maxval (list 1 2 3 5 6 1)) > > > 1 > > > > > > The code looks correct to me, but I must be missing something. What have > > > I done wrong? > > > > > > Your code is 100% correct, conceptually. Sadly, it’s suffering from a > > mistake that I saw many many times in the 90s and before. And that’s > > precisely why we get beginners started on Beginning Student Language in > > DrRacket instead of plain Racket. Try it out for your next few exercises or > > even this one, to see whether the error message would have helped. > > > > — Matthias > > > > > > -- 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.
