add a generic section on exploring package sets

this removes the hard-coded listing, which can later be replaced by
a dynamic one as for the Python interpreters

doc/languages-frameworks/haskell.section.md

@@ -21,42 +21,15 @@ Many “normal” user facing packages written in Haskell, like `niv` or `cachix
 are also exposed at the top level, and there is nothing Haskell specific to
 installing and using them.
 
-All of these packages are originally defined in the `haskellPackages` package
-set and are re-exposed with a reduced dependency closure for convenience.
-(see `justStaticExecutables` or `separateBinOutput` below)
+All of these packages are originally defined in the `haskellPackages` package set.
+The same packages are re-exposed with a reduced dependency closure for convenience (see `justStaticExecutables` or `separateBinOutput` below).
 
-The `haskellPackages` set includes at least one version of every package from [Hackage](https://hackage.haskell.org/) as well as some manually injected packages.
-Haskell packages can be searched on [search.nixos.org](https://search.nixos.org/packages?query=haskellPackages) or listed on the command line with [`nix-instantiate`](https://nixos.org/manual/nix/stable/command-ref/nix-instantiate).
-
-:::{.example #example-list-haskellPackages}
-
-# List all Haskell packages in Nixpkgs
-
-The follwowing command evaluates a Nix expression that maps names of Haskell packages to their version, and displays the result as a JSON.
-
-```shell-session
-nix-instantiate --strict --eval --json --expr "$(cat << EOF
- with (import <nixpkgs> {}); with lib;
- mapAttrs (k: v: v.version)
- (filterAttrs (k: v: isDerivation v) haskellPackages)
-EOF
-)" | jq . | head -10
-```
-
-```console
-{
- "2captcha": "0.1.0.0",
- "3d-graphics-examples": "0.0.0.2",
- "3dmodels": "0.3.0",
- "4Blocks": "0.2",
- "AAI": "0.2.0.1",
- "ABList": "0.0.3",
- "AC-Angle": "1.0",
- "AC-Boolean": "1.1.0",
- "AC-BuildPlatform": "1.1.0",
-```
+:::{.note}
+See [](#chap-language-support) for techniques to explore package sets.
 :::
 
+The `haskellPackages` set includes at least one version of every package from [Hackage](https://hackage.haskell.org/) as well as some manually injected packages.
+
 The attribute names in `haskellPackages` always correspond with their name on
 Hackage. Since Hackage allows names that are not valid Nix without escaping,
 you need to take care when handling attribute names like `3dmodels`.
@@ -79,68 +52,15 @@ How you can help with that is
 described in [Fixing a broken package](#haskell-fixing-a-broken-package).
 -->
 
-`haskellPackages` is built with our default compiler, but we also provide other
-releases of GHC and package sets built with them. You can list all available
-compilers like this:
-
-```console
-$ nix-env -f '<nixpkgs>' -qaP -A haskell.compiler
-haskell.compiler.ghc810 ghc-8.10.7
-haskell.compiler.ghc90 ghc-9.0.2
-haskell.compiler.ghc925 ghc-9.2.5
-haskell.compiler.ghc926 ghc-9.2.6
-haskell.compiler.ghc927 ghc-9.2.7
-haskell.compiler.ghc92 ghc-9.2.8
-haskell.compiler.ghc945 ghc-9.4.5
-haskell.compiler.ghc946 ghc-9.4.6
-haskell.compiler.ghc947 ghc-9.4.7
-haskell.compiler.ghc94 ghc-9.4.8
-haskell.compiler.ghc963 ghc-9.6.3
-haskell.compiler.ghc96 ghc-9.6.4
-haskell.compiler.ghc98 ghc-9.8.1
-haskell.compiler.ghcHEAD ghc-9.9.20231121
-haskell.compiler.ghc8107Binary ghc-binary-8.10.7
-haskell.compiler.ghc865Binary ghc-binary-8.6.5
-haskell.compiler.ghc924Binary ghc-binary-9.2.4
-haskell.compiler.integer-simple.ghc8107 ghc-integer-simple-8.10.7
-haskell.compiler.integer-simple.ghc810 ghc-integer-simple-8.10.7
-haskell.compiler.native-bignum.ghc90 ghc-native-bignum-9.0.2
-haskell.compiler.native-bignum.ghc902 ghc-native-bignum-9.0.2
-haskell.compiler.native-bignum.ghc925 ghc-native-bignum-9.2.5
-haskell.compiler.native-bignum.ghc926 ghc-native-bignum-9.2.6
-haskell.compiler.native-bignum.ghc927 ghc-native-bignum-9.2.7
-haskell.compiler.native-bignum.ghc92 ghc-native-bignum-9.2.8
-haskell.compiler.native-bignum.ghc928 ghc-native-bignum-9.2.8
-haskell.compiler.native-bignum.ghc945 ghc-native-bignum-9.4.5
-haskell.compiler.native-bignum.ghc946 ghc-native-bignum-9.4.6
-haskell.compiler.native-bignum.ghc947 ghc-native-bignum-9.4.7
-haskell.compiler.native-bignum.ghc94 ghc-native-bignum-9.4.8
-haskell.compiler.native-bignum.ghc948 ghc-native-bignum-9.4.8
-haskell.compiler.native-bignum.ghc963 ghc-native-bignum-9.6.3
-haskell.compiler.native-bignum.ghc96 ghc-native-bignum-9.6.4
-haskell.compiler.native-bignum.ghc964 ghc-native-bignum-9.6.4
-haskell.compiler.native-bignum.ghc98 ghc-native-bignum-9.8.1
-haskell.compiler.native-bignum.ghc981 ghc-native-bignum-9.8.1
-haskell.compiler.native-bignum.ghcHEAD ghc-native-bignum-9.9.20231121
-haskell.compiler.ghcjs ghcjs-8.10.7
-```
+`haskellPackages` is built with our default compiler, but we also provide other releases of GHC and package sets built with them.
+Available compilers are collected under `haskell.compiler`.
 
-Each of those compiler versions has a corresponding attribute set built using
+Each of those compiler versions has a corresponding attribute set `packages` built with
 it. However, the non-standard package sets are not tested regularly and, as a
 result, contain fewer working packages. The corresponding package set for GHC
 9.4.5 is `haskell.packages.ghc945`. In fact `haskellPackages` is just an alias
 for `haskell.packages.ghc964`:
 
-```console
-$ nix-env -f '<nixpkgs>' -qaP -A haskell.packages.ghc927
-haskell.packages.ghc927.a50 a50-0.5
-haskell.packages.ghc927.AAI AAI-0.2.0.1
-haskell.packages.ghc927.aasam aasam-0.2.0.0
-haskell.packages.ghc927.abacate abacate-0.0.0.0
-haskell.packages.ghc927.abc-puzzle abc-puzzle-0.2.1
-…
-```
-
 Every package set also re-exposes the GHC used to build its packages as `haskell.packages.*.ghc`.
 
 ### Available package versions {#haskell-available-versions}

doc/languages-frameworks/index.md

@@ -2,6 +2,56 @@
 
 The [standard build environment](#chap-stdenv) makes it easy to build typical Autotools-based packages with very little code. Any other kind of package can be accommodated by overriding the appropriate phases of `stdenv`. However, there are specialised functions in Nixpkgs to easily build packages for other programming languages, such as Perl or Haskell. These are described in this chapter.
 
+Each supported language or software ecosystem has its own package set named `<language or ecosystem>Packages`, which can be explored in various ways:
+
+- Search on [search.nixos.org](https://search.nixos.org/packages)
+
+ For example, search for [`haskellPackages`](https://search.nixos.org/packages?query=haskellPackages) or [`rubyPackages`](https://search.nixos.org/packages?query=rubyPackages).
+
+- Navigate attribute sets with [`nix repl`](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-repl).
+
+ This technique is generally useful to inspect Nix language data structures.
+
+ :::{.example #example-navigte-nix-repl}
+
+ # Navigate Java compiler variants in `javaPackages` with `nix repl`
+
+ ```shell-session
+ $ nix repl '<nixpkgs>' -I nixpkgs=channel:nixpkgs-unstable
+ nix-repl> javaP<tab>
+ nix-repl> javaPackages
+ nix-repl> javaPackages.<tab>
+ javaPackages.compiler javaPackages.openjfx15 javaPackages.openjfx21 javaPackages.recurseForDerivations
+ javaPackages.jogl_2_4_0 javaPackages.openjfx17 javaPackages.openjfx22
+ javaPackages.mavenfod javaPackages.openjfx19 javaPackages.override
+ javaPackages.openjfx11 javaPackages.openjfx20 javaPackages.overrideDerivation
+ ```
+ :::
+
+- List all derivations on the command line with [`nix-env --query`](https://nixos.org/manual/nix/stable/command-ref/nix-env/query).
+
+ `nix-env` is the only convenient way to do that, as it will skip attributes that fail [assertions](https://nixos.org/manual/nix/stable/language/constructs#assertions), such as when a package is [marked as broken](#var-meta-broken).
+
+ :::{.example #example-list-haskellPackages}
+
+ # List all Python packages in Nixpkgs
+
+ The following command lists all [derivations names](https://nixos.org/manual/nix/stable/language/derivations#attr-name) with their attribute path from the latest Nixpkgs rolling release (`nixpkgs-unstable`).
+
+ ```shell-session
+ $ nix-env -qaP -f '<nixpkgs>' -A pythonPackages -I nixpkgs=channel:nixpkgs-unstable
+ ```
+
+ ```console
+ pythonPackages.avahi avahi-0.8
+ pythonPackages.boost boost-1.81.0
+ pythonPackages.caffe caffe-1.0
+ pythonPackages.caffeWithCuda caffe-1.0
+ pythonPackages.cbeams cbeams-1.0.3
+ …
+ ```
+ :::
+
 ```{=include=} sections
 agda.section.md
 android.section.md