[racket-dev] Generics updates

From: Stephen Chang (stchang at ccs.neu.edu)
Date: Thu Aug 1 18:27:58 EDT 2013

Just played a bit with gen:set. It looks great and in particular the
fallback implementations are very convenient.

One comment: the distinction between "primitive" methods and "derived"
methods confused me somewhat. Can you explain the reasoning for
determining which is which?

For example, when I first read the docs, I thought that if I
implemented the primitives, I would get the derived, but that's not
the case since some of the derived methods depend on each other.
Reading the docs more thoroughly, it sort of seems like there's an
implicit separation along the lines of iterability, ie, derived sets
are "iterable" since many of the derived methods require set->stream,
but that's not exactly right either.

On Thu, Jul 25, 2013 at 1:58 PM, Carl Eastlund <cce at ccs.neu.edu> wrote:
> After some fixes, mostly to contracts and documentation, I've pushed the new
> generics and set features to the master branch.
> Carl Eastlund
> On Tue, Jul 23, 2013 at 11:37 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
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