<div dir="ltr">Daniel, I think it'll be worthwhile to direct your attention to this blog entry which goes into more details about why mutable pairs were removed in the first place. <a href="http://blog.racket-lang.org/2007/11/getting-rid-of-set-car-and-set-cdr.html">http://blog.racket-lang.org/2007/11/getting-rid-of-set-car-and-set-cdr.html</a> </div><div class="gmail_extra"> <div class="gmail_quote">On Wed, Mar 5, 2014 at 4:15 PM, Jens Axel Søgaard <<a href="mailto:jensaxel@soegaard.net" target="_blank">jensaxel@soegaard.net</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">(require compatibility/mlist) (mlist 1 2 3) See <a href="http://docs.racket-lang.org/compatibility/mlists.html?q=mlist#%28def._%28%28lib._compatibility%2Fmlist..rkt%29._mlist%29%29" target="_blank">http://docs.racket-lang.org/compatibility/mlists.html?q=mlist#%28def._%28%28lib._compatibility%2Fmlist..rkt%29._mlist%29%29</a> 2014-03-05 22:06 GMT+01:00 Daniel Carrera <<a href="mailto:dcarrera@gmail.com">dcarrera@gmail.com</a>>: <div><div class="h5">> > On 5 March 2014 19:54, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> wrote: >> >> >> Okay, now see mcons. > > > > Neat... mcons, mcar, mcdr, mpair, set-mcar!, set-mcdr! > > I notice that there is no mlist. Is there a shortcut similar to '(1 2 3) to > quote a list in a way that makes mutable pairs instead of regular pairs? > > Cheers, > Daniel. > > >> >> >> On Mar 5, 2014, at 1:53 PM, Daniel Carrera wrote: >> >> I see. >> >> k is '(42 2 3) while l is '(1 2 3). This is what I expected to happen, but >> it is clearly not what was supposed to happen. I just tried the same example >> with Chicken, and for Chicken both k and l are equal to '(42 2 3). >> >> Thanks for the explanation. >> >> Cheers, >> Daniel. >> >> On 5 March 2014 19:24, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> wrote: >>> >>> >>> Try >>> >>> (define l (list 1 2 3)) >>> (define k l) >>> >>> Now what does (set-car! k 42) do? What should it do? >>> >>> >>> On Mar 5, 2014, at 1:23 PM, Daniel Carrera wrote: >>> >>> But isn't the final effect the same? The pair may be immutable, but I can >>> make a new pair and bind it to the old variable. The main difference that I >>> can see is that what I wrote is a macro, while I believe set-car! is >>> supposed to be a function. That could potentially break code. >>> >>> Cheers, >>> Daniel. >>> >>> >>> On 5 March 2014 19:18, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu">matthias@ccs.neu.edu</a>> wrote: >>>> >>>> >>>> No, set! mutates variable bindings while set-car! mutates cons cells >>>> (the first slot of a data structure). >>>> >>>> >>>> On Mar 5, 2014, at 1:13 PM, Daniel Carrera wrote: >>>> >>>> > Hello, >>>> > >>>> > My understanding is that Racket intentionally does not provide >>>> > set-car! and set-cdr! and that this is one of the ways in which Racket is >>>> > not fully compatible with Scheme. >>>> > >>>> > Am I right to think that it is trivially easy to add these features to >>>> > Racket? Specifically, I'm thinking of: >>>> > >>>> > >>>> > (define-syntax set-car! >>>> > (syntax-rules () >>>> > ((_ l new_car) (set! l (cons new_car (cdr l)))))) >>>> > >>>> > (define-syntax set-cdr! >>>> > (syntax-rules () >>>> > ((_ l new_cdr) (set! l (cons (car l) new_cdr))))) >>>> > >>>> > >>>> > Or did I miss something? >>>> > >>>> > Cheers, >>>> > Daniel. >>>> > -- >>>> > When an engineer says that something can't be done, it's a code phrase >>>> > that means it's not fun to do. >>>> > ____________________ >>>> > Racket Users list: >>>> > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> >>>> >>> >>> >>> >>> -- >>> When an engineer says that something can't be done, it's a code phrase >>> that means it's not fun to do. >>> >>> >> >> >> >> -- >> When an engineer says that something can't be done, it's a code phrase >> that means it's not fun to do. >> >> > > > > -- > When an engineer says that something can't be done, it's a code phrase that > means it's not fun to do. > > ____________________ > Racket Users list: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> > -- </div></div>-- Jens Axel Søgaard <div class="HOEnZb"><div class="h5"> ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </div></div></blockquote></div> </div>