Problem Statement

Rename:

This should be done twice:   once "here", i.e. in the current working directory and once in the filesystem root. It can be assumed that the user has the rights to do so. (In unix-type systems, only the user root would have sufficient permissions in the filesystem root.)

Let's start with the solution:

let () =
  Sys.rename "input.txt" "output.txt";
  Sys.rename "docs" "mydocs";
  Sys.rename "/input.txt" "/output.txt";
  Sys.rename "/docs" "/mydocs";