But 'list-union' is not a generic operation so it isn't surprising that this didn't work. To do this generically, you'd need to use 'set-union'.
Sam On Aug 22, 2013 7:59 AM, "J. Ian Johnson" <i...@ccs.neu.edu> wrote: > The problem manifested itself when I got an exception that in-list can't > be called on (set), which really confused me. (set? '()) answered true, so > it tried to do (list-union '() (set)), which failed. > Generic sets as they are don't work generically. Some action should be > taken. Either set? means what it once did, or we do some awfully slow > multiple dispatch for set operations. My bias shows. > -Ian > ----- Original Message ----- > From: "Matthew Flatt" <mfl...@cs.utah.edu> > To: "Carl Eastlund" <c...@ccs.neu.edu> > Cc: "J. Ian Johnson" <i...@ccs.neu.edu>, "dev" <dev@racket-lang.org> > Sent: Thursday, August 22, 2013 7:22:25 AM GMT -05:00 US/Canada Eastern > Subject: Re: [racket-dev] Lists aren't sets, but have set-like operations > > How much should we prioritize backward compatibility in this case? > > One possibility is to make `set?' mean `hash-set?', and add > `generic-set?' in place of the current `set?'. That's uglier, > obviously, but it would be better if we want to prioritize backward > compatibility. > > At Wed, 21 Aug 2013 19:14:06 -0400, Carl Eastlund wrote: > > Ah, yes. The set? predicate no longer distinguishes a representation. > > There are several predicates for the original set type, now called "hash > > sets": set-eq?, set-eqv?, set-equal?, set-mutable?, set-immtuable?, and > > set-weak?. I didn't add the basic "hash-set?", but perhaps I should. > It's > > a weird name, since "hash-set" and "hash-set!" are already existing, > > unrelated functions. > > > > Carl Eastlund > > > > > > On Wed, Aug 21, 2013 at 7:08 PM, J. Ian Johnson <i...@ccs.neu.edu> > wrote: > > > > > Okay, I can abide. However, that doesn't really get at my frustration. > I'm > > > using the set constructor, that appears to now be an > immutable-custom-set > > > with make-immutable-hash as its make-table. So what I'm looking for is > not > > > set?, but set-immutable?, as it's a distinct (family of) struct types > that > > > won't clash with the primitive data that I'm otherwise using. > > > -Ian > > > ----- Original Message ----- > > > From: "Carl Eastlund" <c...@ccs.neu.edu> > > > To: "J. Ian Johnson" <i...@ccs.neu.edu> > > > Cc: "dev" <dev@racket-lang.org> > > > Sent: Wednesday, August 21, 2013 6:58:56 PM GMT -05:00 US/Canada > Eastern > > > Subject: Re: [racket-dev] Lists aren't sets, but have set-like > operations > > > > > > > > > Ian, sets are now a generic datatype, like dictionaries. Association > lists > > > are dictionaries, and lists are now sets. They're also streams and > > > sequences. They're not just "set-like". > > > > > > > > > > > > Carl Eastlund > > > > > > > > > On Wed, Aug 21, 2013 at 6:56 PM, J. Ian Johnson < i...@ccs.neu.edu > > > > wrote: > > > > > > > > > I just wasted about 2 hours tracking down a bug that ended up being > due to > > > (set? '()) now evaluating to #t. I have no problems with set-union, > > > intersection, etc. being defined for lists, but to treat lists as sets > > > always is perverse to me. The contracts for set operations should use > > > set-like? for (or/c set? list?) and keep the two constructions > separate. > > > > > > This conflation is almost as bad as treating empty list as false. > > > > > > -Ian > > > _________________________ > > > Racket Developers list: > > > http://lists.racket-lang.org/dev > > > > > > > > > > > > > > _________________________ > > Racket Developers list: > > http://lists.racket-lang.org/dev > _________________________ > Racket Developers list: > http://lists.racket-lang.org/dev >
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