No, it doesn't seem to be using the fallback in this case. ianj@sampson:~/racket/racket/bin$ ./racket -il xrepl Welcome to Racket v5.90.0.8. -> (set-union '() (set)) ; in-list: contract violation ; expected: list? ; given: (set) ; [,bt for context] ->
-Ian ----- Original Message ----- From: "Sam Tobin-Hochstadt" <sa...@cs.indiana.edu> To: "J. Ian Johnson" <i...@ccs.neu.edu>, "Carl Eastlund" <c...@ccs.neu.edu> Cc: dev@racket-lang.org, "Matthew Flatt" <mfl...@cs.utah.edu> Sent: Thursday, August 22, 2013 8:51:30 AM GMT -05:00 US/Canada Eastern Subject: Re: [racket-dev] Lists aren't sets, but have set-like operations Wait, `set-union` of two different set representations doesn't work? Sam On Thu, Aug 22, 2013 at 8:07 AM, J. Ian Johnson <i...@ccs.neu.edu> wrote: > You misunderstand. I used set-union, but single dispatch saw '() and used > list-union for the '() (set) combination. > -Ian > ----- Original Message ----- > From: "Sam Tobin-Hochstadt" <sa...@cs.indiana.edu> > To: "J. Ian Johnson" <i...@ccs.neu.edu> > Cc: dev@racket-lang.org, "Matthew Flatt" <mfl...@cs.utah.edu> > Sent: Thursday, August 22, 2013 8:02:50 AM GMT -05:00 US/Canada Eastern > Subject: Re: [racket-dev] Lists aren't sets, but have set-like operations > > > > 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 _________________________ Racket Developers list: http://lists.racket-lang.org/dev
