let
  # Recursive fibonacci (not memoized)
  fib = n:
    if n <= 1
    then n
    else fib (n - 1) + fib (n - 2);

  # List operations
  numbers = [1 2 3 4 5 6 7 8 9 10];
  doubled = builtins.map (x: x * 2) numbers;

  # Attrset operations
  base = {
    a = 1;
    b = 2;
    c = 3;
  };
  extended =
    base
    // {
      d = 4;
      e = 5;
    };

  # String operations
  greeting = "Hello";
  message = "${greeting}, World!";
in {
  fibonacci_10 = fib 10;
  inherit doubled extended message;
}