nixpkgs/doc/languages-frameworks/chicken.section.md
pennae 052bb41410 doc: assign ids to many headings
without stable ids on headings we cannot generate stable links to these
headings. nrd complains about this, but the current docbook workflow
does not.

a few generated ids remain, mostly in examples and footnotes. most of
the examples are generated by nixdoc (which has since gained MD export
functions, and the MD export does generate IDs).
2023-03-27 22:39:11 +02:00

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# CHICKEN {#sec-chicken}
[CHICKEN](https://call-cc.org/) is a
[R⁵RS](https://schemers.org/Documents/Standards/R5RS/HTML/)-compliant Scheme
compiler. It includes an interactive mode and a custom package format, "eggs".
## Using Eggs {#sec-chicken-using}
Eggs described in nixpkgs are available inside the
`chickenPackages.chickenEggs` attrset. Including an egg as a build input is
done in the typical Nix fashion. For example, to include support for [SRFI
189](https://srfi.schemers.org/srfi-189/srfi-189.html) in a derivation, one
might write:
```nix
buildInputs = [
chicken
chickenPackages.chickenEggs.srfi-189
];
```
Both `chicken` and its eggs have a setup hook which configures the environment
variables `CHICKEN_INCLUDE_PATH` and `CHICKEN_REPOSITORY_PATH`.
## Updating Eggs {#sec-chicken-updating-eggs}
nixpkgs only knows about a subset of all published eggs. It uses
[egg2nix](https://github.com/the-kenny/egg2nix) to generate a
package set from a list of eggs to include.
The package set is regenerated by running the following shell commands:
```
$ nix-shell -p chickenPackages.egg2nix
$ cd pkgs/development/compilers/chicken/5/
$ egg2nix eggs.scm > eggs.nix
```
## Adding Eggs {#sec-chicken-adding-eggs}
When we run `egg2nix`, we obtain one collection of eggs with
mutually-compatible versions. This means that when we add new eggs, we may
need to update existing eggs. To keep those separate, follow the procedure for
updating eggs before including more eggs.
To include more eggs, edit `pkgs/development/compilers/chicken/5/eggs.scm`.
The first section of this file lists eggs which are required by `egg2nix`
itself; all other eggs go into the second section. After editing, follow the
procedure for updating eggs.