buildPerlPackage not working

[poperigby]

I'm trying to build this package...

{
    buildPerlPackage,
    ...
}:

buildPerlPackage {
    pname = "indent-changer";
    version = "0.1.0";
    src = ./indent-changer.pl;
}

...but it's failing with this error:

error:
       … while evaluating a branch condition
         at /nix/store/84m9nfg7kamv5va1fkk2iszbn5q2mavh-source/flake.nix:43:15:
           42|             (name: value:
           43|               if isAttrs value then lhs.${name} or { } // value
             |               ^
           44|               else if isList value then lhs.${name} or [ ] ++ value

       … while calling the 'isAttrs' builtin
         at /nix/store/84m9nfg7kamv5va1fkk2iszbn5q2mavh-source/flake.nix:43:18:
           42|             (name: value:
           43|               if isAttrs value then lhs.${name} or { } // value
             |                  ^
           44|               else if isList value then lhs.${name} or [ ] ++ value

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'buildPerlPackage' missing
       at /nix/store/j54hy8ncy0mjxvcq7axmwss4ngpdzhyk-packages/indent-changer/default.nix:6:1:
            5|
            6| pkgs.buildPerlPackage {
             | ^
            7|     pname = "indent-changer";

This is my directory structure:

.
└── packages
    └── indent-changer
        ├── default.nix
        └── indent-changer.pl