{ pkgs, config, ... }: {
  env.GREET = "determinism";

  packages = [ 
    pkgs.ncdu
  ];

  enterShell = ''
    echo hello ${config.env.GREET}
    ncdu --version
  '';
}

$ devenv shell
hello determinism
ncdu 2.3

{
  scripts.nushell-greet = {
    exec = ''
      def greet [name] {
        ["hello" $name]
      }
      greet "world"
    '';
    package = pkgs.nushell;
    binary = "nu";
    description = "Greet in Nu Shell";
  };
}

{ pkgs, ... }: {
  packages = [ 
    pkgs.mkdocs
  ];

  processes = {
    docs.exec = "mkdocs serve";
  };
}

{ pkgs, ... }: {
  services.postgres = {
    enable = true;
    package = pkgs.postgresql_15;
    initialDatabases = [{ name = "mydb"; }];
    extensions = extensions: [
      extensions.postgis
      extensions.timescaledb
    ];
    settings.shared_preload_libraries = "timescaledb";
    initialScript = "CREATE EXTENSION IF NOT EXISTS timescaledb;";
  };
  
  processes.docs.exec = "${pkgs.mkdocs}/bin/mkdocs serve";

  enterTest = ''
    wait_for_port 8000
    curl http://localhost:8000 | grep "Hello, world!"
  '';
}

{ pkgs, ... }: {
  languages.haskell.enable = true;
  languages.haskell.package = 
    pkgs.haskell.compiler.ghc9101;
  
  services.ghcid.myexe = {
    package = "mypackage";
    components = [ "lib" "exe:myexe" ];
    args = [ "serve" ];
    stack.enable = true;
  };
  
  pre-commit.hooks = {
    ormolu.enable = true;
    cabal-fmt.enable = true;
  };
}

executable readme
  main-is:        README.lhs
  build-depends:  base, mylib
  ghc-options:    -pgmL markdown-unlit
  build-tool-depends: markdown-unlit:markdown-unlit