error:
       … computing fib(4)

       … while calling the 'add' builtin
         at /pwd/in.nix:7:8:
            6|       # note: we use builtins.add explicitly because it creates more frames than (+)
            7|       (builtins.add (fib (n - 1)) (fib (n - 2)));
             |        ^
            8| in

       … computing fib(3)

       … computing fib(2)

       … computing fib(1)

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: assertion failed
       at /pwd/in.nix:3:5:
            2|   fib = n:
            3|     assert n > 0;
             |     ^
            4|     builtins.addErrorContext