anchor.diff:  
         environment.systemPackages = [ cfg.package ];
   
  -      programs.zsh.interactiveShellInit = with builtins; ''
  +      programs.zsh.interactiveShellInit = ''
           # oh-my-zsh configuration generated by NixOS
           export ZSH=${cfg.package}/share/oh-my-zsh
   
  
positive.code:         };
  
          custom = mkOption {
            default = "";
            type = types.str;
            description = ''
              Path to a custom oh-my-zsh package to override config of oh-my-zsh.
            '';
          };
  
  
negative.code: 
          source $ZSH/oh-my-zsh.sh
        '';
  
        assertions = [
          {
            assertion = cfg.custom != null -> cfg.customPkgs == [];
            message = "If `cfg.custom` is set for `ZSH_CUSTOM`, `customPkgs` can't be used!";
          }
        ];
  
      };
    }
  