Thank you Stephen. The code does not work in general. I know how to do it now.
On Thu, Jun 2, 2011 at 7:45 AM, Stephen Bloch <sbl...@adelphi.edu> wrote: > > On Jun 2, 2011, at 9:11 AM, Yingjian Ma wrote: > > > Here is another question. In (lambda (ls), it seems ls took the value > from v. How does Racket know not pass x to ls as the argument? > > "helper" is defined as "(lambda (ls) ...)" > The only place you call "helper", you give it "(vector->list v)"; you don't > pass it x, so it doesn't take x. > > > Does it alway takes the right variable? > > No, it always takes what is explicitly passed in as arguments :-) > > > Also, I want code to keep all the letters that is not a. It does not > work for > > (test 'a #(b c a b a d)). The result is '(c b). If you know how to > generalize it, please let me know. > > > In fact, the program you showed us has quite a number of problems: try > (test 'a #(b)) > (test 'a #(a a)) > (test 'a #(a b a c)) > for example. > > I would fix this program by starting over from scratch: the program as it > stands is not only buggy but too long and complicated. My solution, and the > one I would expect my beginning students to come up with, is about 140 > characters long, not including contract and test cases. > > > Stephen Bloch > sbl...@adelphi.edu > >
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