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Matthew Flatt 2b79ba6d4f add ephemeron hash tables 
Weak hash tables retain keys weakly, but they hold each corresponding
value strongly as long as the key is accessible. As a result, weak
hash tables suffer from the key-in-value problem: if the value refers
to the key, the key cannot become inaccesible and be removed from the
table.

Previously, the way around that problem was to map a key to an
ephemeron that combines the key and value. The extra cost of involving
ephemerons (a constant factor) is why ephemerons storage is not the
default behavior of weak hash tables.[*] Having ephemeron hash tables
as a distinct variant avoids imposing a cost where its not needed, and
compared to using explicit ephemerons, it's easier to drop into a
program that was written to use strong or merely weak hash tables.

For Racket CS, the change is especially straightforward, because
ephemeron tables already exist in Chez Scheme (at least for the Racket
variant, in the case of eqv- and equal-based tables).

[*] Also, non-emphemeron hash tables turn out to be needed for certain
    finalization tasks.
2021-02-27 19:08:05 -07:00
.github ci: build CS for iOS during PR CI 2021-01-19 07:08:27 -05:00
pkgs add ephemeron hash tables 2021-02-27 19:08:05 -07:00
racket add ephemeron hash tables 2021-02-27 19:08:05 -07:00
.gitattributes Don't include git files in archives. 2010-05-12 01:46:05 -04:00
.gitignore Fix typo. 2019-06-21 12:32:37 -05:00
.lgtm.yml Fetch PB to start LGTM build 2020-08-07 12:17:17 +02:00
.mailmap Minor metadata changes. 2019-10-15 08:09:32 -04:00
.makefile add structure-type sealing 2021-02-13 08:46:31 -07:00
build.md build-instruction typos and clarifications 2020-12-27 19:08:19 -07:00
LICENSE update LICENSE to use "CS" and "BC" 2021-01-15 09:32:59 -07:00
Makefile add structure-type sealing 2021-02-13 08:46:31 -07:00
README.md Fix README 2020-09-06 09:03:42 -04:00

README.md

Racket is a general-purpose programming language and an ecosystem for language-oriented programming.

This repository holds the source code for the core of Racket plus some related packages. The rest of the Racket distribution source code is in other repositories, mostly under the Racket GitHub organization.

Quick Start

Pre-built versions of Racket for a variety of operating systems and architectures, as well as convenient source distributions are available at

https://download.racket-lang.org

Racket comes with extensive documentation, including several tutorials. You can read all of this documentation, as well as documentation for third-party packages at

https://docs.racket-lang.org

Building from Source

For information on building Racket from this repository, see the Build Guide.

Contributing

Contribute to Racket by submitting a pull request, joining the development mailing list, or visiting the IRC or Slack channels.

By making a contribution, you are agreeing that your contribution is licensed under the LGPLv3, Apache 2.0, and MIT licenses. Those licenses are available in this repository in the files racket/src/LICENSE-LGPL.txt, racket/src/LICENSE-APACHE.txt, and racket/src/LICENSE-MIT.txt.

See the Racket Build Guide for more guidance on contributing.

The Friendly Environment Policy contains guidelines on expected behavior within the Racket community.

License

Racket is free software; see LICENSE for more details.