Problem Statement

Create a directory and any missing parents. This task is named after the posix mkdir -p command, and several libraries which implement the same behavior. Please implement a function of a single path string (for example ./path/to/dir) which has the above side-effect. If the directory already exists, return successfully. Ideally implementations will work equally well cross-platform (on windows, linux, and OS X). It's likely that your language implements such a function as part of its standard library. If so, please also show how such a function would be implemented.

Let's start with the solution:

let rec mkdir_p path perm =
 if path <> "" then
    try Unix.mkdir path perm with
    | Unix.Unix_error (EEXIST, _, _) when Sys.is_directory path -> ()
    | Unix.Unix_error (ENOENT, _, _) ->
      mkdir_p (Filename.dirname path) perm;
      Unix.mkdir path perm