[racket-dev] Lists aren't sets, but have set-like operations

From: Carl Eastlund (cce at ccs.neu.edu)
Date: Wed Aug 21 19:14:06 EDT 2013

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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> http://lists.racket-lang.org/dev
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