Mix and match older tools from nixpkgs

shell.nix

{ pkgs ? import <nixpkgs> {} }:

let
  graalvm21_2_0 = import (builtins.fetchGit {
    # Descriptive name to make the store path easier to identify
    name = "graalvm-21.2.0";
    url = "https://github.com/NixOS/nixpkgs";
    ref = "refs/heads/nixpkgs-unstable";
    rev = "e4dda76e6397fb1e30b907abeaf6a72bb055a1e6";
  }) {};
  babashka0_6_5 = import (builtins.fetchGit {
    # Descriptive name to make the store path easier to identify
    name = "babashka0.6.5";
    url = "https://github.com/NixOS/nixpkgs";
    ref = "refs/heads/nixpkgs-unstable";
    rev = "1b323e036ce3bd0816e79c1cdef02eb1ba063f57";
  }) {};
in pkgs.mkShell {
  # nativeBuildInputs is usually what you want -- tools you need to run
  nativeBuildInputs = [ graalvm21_2_0.graalvm11-ce babashka0_6_5.babashka ];
}