These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.99 s (backtrack: 0/20).

[ebuild  N     ] dev-lang/ocaml-5.5.1:0/5.5.1::gentoo  USE="ocamlopt -emacs -flambda -latex -test -xemacs" 6457 KiB
[ebuild  N     ] dev-ml/dune-3.23.1:0/3.23.1::gentoo  USE="-emacs -test" 3624 KiB
[ebuild  N     ] dev-ml/bigarray-compat-1.1.0::gentoo  USE="ocamlopt" 2 KiB
[ebuild  N     ] dev-ml/mmap-1.2.0-r1:0/1.2.0::gentoo  USE="ocamlopt" 15 KiB

Total: 4 packages (4 new), Size of downloads: 10097 KiB