[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 <ianj at 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" <cce at ccs.neu.edu>
> > To: "J. Ian Johnson" <ianj at ccs.neu.edu>
> > Cc: "dev" <dev at 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 < ianj at 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
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> >
> >
> >
> >
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