channel changing

channels.nix

let mapAttrs = f: set: builtins.listToAttrs (
      map (attr: { name = attr; value = f attr set.${attr}; })
          (builtins.attrNames set));
    channels = {
      aardvark = "13.10";
      baboon = "14.04";
      caterpillar = "14.12";
      dingo = "15.09";
      emu = "16.03";
      flounder = "16.09";
      gorilla = "17.03";
      hummingbird = "17.09";
      impala = "18.03";
      jellyfish = "18.09";
      koi = "19.03";
      # loris = "19.09";
    };
in mapAttrs (n: v:
     (import (builtins.fetchTarball "https://nixos.org/channels/nixos-${v}/nixexprs.tar.xz") {}).pkgs)
   channels

tests

> $(nix-build channels.nix -A aardvark.hello)/bin/hello
hello: loadlocale.c:129: _nl_intern_locale_data: Assertion `cnt < (sizeof (_nl_value_type_LC_TIME) / sizeof (_nl_value_type_LC_TIME[0]))' failed.
aborted
> $(nix-build channels.nix -A baboon.hello)/bin/hello
hello: loadlocale.c:129: _nl_intern_locale_data: Assertion `cnt < (sizeof (_nl_value_type_LC_TIME) / sizeof (_nl_value_type_LC_TIME[0]))' failed.
aborted
> $(nix-build channels.nix -A caterpillar.hello)/bin/hello
hello: loadlocale.c:129: _nl_intern_locale_data: Assertion `cnt < (sizeof (_nl_value_type_LC_TIME) / sizeof (_nl_value_type_LC_TIME[0]))' failed.
aborted
> $(nix-build channels.nix -A dingo.hello)/bin/hello
Hello, world!
> $(nix-build channels.nix -A emu.hello)/bin/hello
Hello, world!
> $(nix-build channels.nix -A flounder.hello)/bin/hello
Hello, world!
> $(nix-build channels.nix -A gorilla.hello)/bin/hello
Hello, world!
> $(nix-build channels.nix -A hummingbird.hello)/bin/hello
Hello, world!
> $(nix-build channels.nix -A impala.hello)/bin/hello
Hello, world!
> $(nix-build channels.nix -A jellyfish.hello)/bin/hello
Hello, world!
> $(nix-build channels.nix -A koi.hello)/bin/hello
Hello, world!