78 lines
2.6 KiB
Markdown
78 lines
2.6 KiB
Markdown
# CHICKEN {#sec-chicken}
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[CHICKEN](https://call-cc.org/) is a
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[R⁵RS](https://schemers.org/Documents/Standards/R5RS/HTML/)-compliant Scheme
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compiler. It includes an interactive mode and a custom package format, "eggs".
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## Using Eggs {#sec-chicken-using}
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Eggs described in nixpkgs are available inside the
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`chickenPackages.chickenEggs` attrset. Including an egg as a build input is
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done in the typical Nix fashion. For example, to include support for [SRFI
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189](https://srfi.schemers.org/srfi-189/srfi-189.html) in a derivation, one
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might write:
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```nix
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buildInputs = [
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chicken
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chickenPackages.chickenEggs.srfi-189
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];
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```
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Both `chicken` and its eggs have a setup hook which configures the environment
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variables `CHICKEN_INCLUDE_PATH` and `CHICKEN_REPOSITORY_PATH`.
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## Updating Eggs {#sec-chicken-updating-eggs}
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nixpkgs only knows about a subset of all published eggs. It uses
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[egg2nix](https://github.com/the-kenny/egg2nix) to generate a
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package set from a list of eggs to include.
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The package set is regenerated by running the following shell commands:
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```
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$ nix-shell -p chickenPackages.egg2nix
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$ cd pkgs/development/compilers/chicken/5/
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$ egg2nix eggs.scm > eggs.nix
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```
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## Adding Eggs {#sec-chicken-adding-eggs}
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When we run `egg2nix`, we obtain one collection of eggs with
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mutually-compatible versions. This means that when we add new eggs, we may
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need to update existing eggs. To keep those separate, follow the procedure for
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updating eggs before including more eggs.
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To include more eggs, edit `pkgs/development/compilers/chicken/5/eggs.scm`.
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The first section of this file lists eggs which are required by `egg2nix`
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itself; all other eggs go into the second section. After editing, follow the
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procedure for updating eggs.
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## Override Scope {#sec-chicken-override-scope}
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The chicken package and its eggs, respectively, reside in a scope. This means,
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the scope can be overridden to effect other packages in it.
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This example shows how to use a local copy of `srfi-180` and have it affect
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all the other eggs:
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```nix
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let
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myChickenPackages = pkgs.chickenPackages.overrideScope' (self: super: {
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# The chicken package itself can be overridden to effect the whole ecosystem.
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# chicken = super.chicken.overrideAttrs {
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# src = ...
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# };
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chickenEggs = super.chickenEggs.overrideScope' (eggself: eggsuper: {
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srfi-180 = eggsuper.srfi-180.overrideAttrs {
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# path to a local copy of srfi-180
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src = ...
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};
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});
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});
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in
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# Here, `myChickenPackages.chickenEggs.json-rpc`, which depends on `srfi-180` will use
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# the local copy of `srfi-180`.
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# ...
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```
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