[racket-dev] Generics updates

From: J. Ian Johnson (ianj at ccs.neu.edu)
Date: Wed Oct 2 15:31:24 EDT 2013

This means I can't interchange between mutable and immutable sets for my functions that only need to read generic sets, unless we further subdivide and have gen:set-query gen:set-constructor gen:set-mconstruct.

----- Original Message -----
From: "Jay McCarthy" <jay.mccarthy at gmail.com>
To: "Carl Eastlund" <cce at ccs.neu.edu>
Cc: "Racket Developers" <dev at racket-lang.org>
Sent: Wednesday, October 2, 2013 3:23:07 PM GMT -05:00 US/Canada Eastern
Subject: Re: [racket-dev] Generics updates

Regarding a point from RacketCon, I don't like that gen:set includes
functions like set-add! and set-remove!. I think that sets with
mutations are subclass of get:set and we should have a separate
gen:mset (or something) interface for mutable versions.

I dislike that an obvious implementation of sets, hash tables, are not
sets to gen:set, because there are operations that cannot be performed
on them.

I think that "X implements generic G" should imply "All functions of G
work on X". But this is not the case with gen:set and hasheq sets, for


On Tue, Jul 23, 2013 at 9:37 AM, Carl Eastlund <cce at ccs.neu.edu> wrote:
> My work on adding gen:set, and related changes to define-generics and
> gen:dict, is ready for review and (hopefully) to push to the master branch.
> The branch moved in the process of cleaning things up, it's now at:
>   https://github.com/carl-eastlund/racket/tree/generics-from-scratch
> (The "from scratch" just refers to the process of rebuilding the git
> history, I didn't go out of my way to rewrite anything in the code base from
> scratch, although in some places a lot of code did move around.)
> What's new in the branch:
> - Generics now support a few new options
>   - #:fallbacks specifies fallback method implementations for instances with
> no implementation
>   - #:fast-defaults specifies instances on a "fast path", useful for
> built-in types
>   - #:defined-predicate gives a more intuitive and efficient interface than
> #:defined-table
>   - #:derive-property allows generics to piggy-back on existing struct
> properties
> - Sets are now a generic datatype through gen:set
>   - lists are now sets
>   - the built-in set types are now documented as "hash sets"
>   - there are mutable and weak hash sets
>   - you can define new set types quickly with define-custom-set-types
>   - most set operations are now methods with fallbacks
>   - sets now support -copy and -clear operations, plus mutating [!] versions
> of operations
> - Dictionaries have a few changes
>   - new macro define-custom-hash-types [*]
>   - most dict operations are now methods with fallbacks
>   - dicts now support -copy, -clear, -clear!, and -empty? operations
> I've run some benchmarks and performance of the various generic operations
> are comparable to the current HEAD, so there should be no major performance
> changes with this patch.
> [*] I've added define-custom-hash-types and define-custom-set-types rather
> than just adding make-custom-set akin to make-custom-hash because
> make-custom-hash is hard to use.  The documented behavior -- that any custom
> hash is equal to any other created with the same bindings and predicates /
> hash functions -- was never true and can be expensive or at least tricky to
> implement.  It seemed more sensible to just remove the erroneous
> documentation on make-custom-hash, and add the definition form to create
> constructors for new, explicitly-compatible dict and set types.  Both
> definition forms bind predicates and constructors for new (set or dict)
> types with immutable, mutable, and weak variants that inter-operate.
> If there are no serious issues brought up in the next day or two, I'll push
> it to the development branch, since our current release process isn't
> following HEAD.
> Carl Eastlund
> _________________________
>   Racket Developers list:
>   http://lists.racket-lang.org/dev

Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University

"The glory of God is Intelligence" - D&C 93
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