anchor.diff:        description = "Enable fzf keybinding for Ctrl-r history search.";
       };
   
  +    programs.zsh.enableSyntaxHighlighting = mkOption {
  +      type = types.bool;
  +      default = false;
  +      description = "Enable zsh-syntax-highlighting.";
  +    };
  +
     };
   
     config = mkIf cfg.enable {
  
positive.code:       ${optionalString cfg.enableCompletion "autoload -U compinit && compinit"}
        ${optionalString cfg.enableBashCompletion "autoload -U bashcompinit && bashcompinit"}
  
        # Read system-wide modifications.
        if test -f /etc/zshrc.local; then
          . /etc/zshrc.local
  
negative.code:     environment.systemPackages =
        [ # Include zsh package
          pkgs.zsh
        ] ++ optional cfg.enableCompletion pkgs.nix-zsh-completions
          ++ optional cfg.enableSyntaxHighlighting pkgs.zsh-syntax-highlighting;
  
      environment.loginShell = mkDefault "${shell}/bin/zsh -l";
      environment.variables.SHELL = mkDefault "${shell}/bin/zsh";
  