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 <matth...@ccs.neu.edu> 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: > > http://lists.racket-lang.org/users > > > > > -- > When an engineer says that something can't be done, it's a code phrase that > means it's not fun to do.
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