Nix flake in guide fails

[agj]

Hello! This is my first time trying out Melange and OCaml. I'm following the "getting started" guide, tried the Nix flake, copied and pasted literally, and I get the following error output:

warning: Git tree '/Users/Ale/mydata/personal/interactive/other/userscripts' is dirty
error: builder for '/nix/store/gp5c6abv82fvxgi5xncj0xv7x5dbkp6l-ocaml5.1.1-melange-dev.drv' failed with exit code 1;
       last 10 log lines:
       > Running phase: configurePhase
       > no configure script, doing nothing
       > Running phase: buildPhase
       > File "vendor/dune", lines 39-40, characters 3-54:
       > 39 |    annot
       > 40 |    (:include ../gen/optional_5_2_modules.txt))))
       > Error: The following modules must be listed here as they don't have an
       > implementation:
       > - Value_rec_types
       >
       For full logs, run 'nix log /nix/store/gp5c6abv82fvxgi5xncj0xv7x5dbkp6l-ocaml5.1.1-melange-dev.drv'.
error (ignored): error: cannot unlink '/private/tmp/nix-build-ocaml5.1.1-ocamlc-loc-3.16.0.drv-3/dune-3.16.0/src': Directory not empty
error (ignored): error: cannot unlink '/private/tmp/nix-build-ocaml5.1.1-chrome-trace-3.16.0.drv-3/dune-3.16.0/test/blackbox-tests/test-cases': Directory not empty
error: 1 dependencies of derivation '/nix/store/k9nai3rfzllccw2ah6qbv9jxl9dbzkgh-nix-shell-env.drv' failed to build

System info:

 - system: `"x86_64-darwin"`
 - host os: `Darwin 21.6.0, macOS 10.16`
 - multi-user?: `yes`
 - sandbox: `no`
 - version: `nix-env (Nix) 2.18.8`

Any help would be appreciated! 🙏