Motivation for this change

tcltk was switched off for Darwin in R when support for Darwin was added in a225a65.

I have tested this patch on Catalina (10.15) and High Sierra (10.13). R successfully builds and the following program displays a frame

Test done:

nix-shell -p '(import ./. {}).R' --pure --run R

> library(tcltk)
> tkframe(tktoplevel())

Note existence of frame.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @