On Thu, Nov 11, 2010 at 1:14 PM, Eli Barzilay <e...@barzilay.org> wrote: >> I got inspired by the #:when form in `for' loops that flattens >> nesting, and wrote a `cond*' macro that allows this instead: >> >> (cond* [... some stuff ...] >> #:with (define m ...) >> [(... something about m ...) (... something using m ...)] >> ... more things referring to m ...) >> >> It's more general, since it doesn't require encoding the condition >> you want to test as a truthiness value. Also, the `define' doesn't >> have to be a `define' - it can be any legal expression. > > So, you advocate eliminating `member' etc for predicates (why I > started with saying that this is much stickier than just adding a > `member?'). So we started with > > (cdr (assq x alist)) > > then Scheme upgraded this to > > (cond [(assq x alist) => cdr] > [else #f]) > > and you suggest continuing with > > (cond #:with (define p (assq x alist)) > [(pair? p) (cdr p)] > [else #f]) > > or, with more well-behaved proper sub lists > > (cond #:with (define p (assq x alist)) > [(not (eq? p #f)) (cadr p)] > [else #f]) > > (Yes, you can still use `pair?' but that would be ugly for the same > reason.) > > I also wonder how many newbies (or people that just want to type less) > will fall into traps like > > (if (member? x l) > (+ 1 (find x l)) > 0) > > My loud "ugh" should be expected now.
(dict-ref x alist) --Carl _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
