It can happen if you happen to install a recent compiler and that package manager has not done the work(probably changing the bounds) to update in opam repo. >

It can happen if you happen to install a recent compiler and that package manager has not done the work(probably changing the bounds) to update in opam repo. > I don't understand how language developers don't prioritize package management in 2018 As you already know, Ocaml already has a decent package manager opam, this same situation will happen in any language where the packages get stale(e.g. in rust you installed something used nightly features that didn't make it mainstream).