Using OCaml unix library

unix_fun.ml

let (>>) f g a = a |> f |> g

let list_all = Sys.readdir >> Array.to_list >> List.filter Sys.is_directory

let rec read_all handle =
    match Unix.readdir handle with 
    | "." | ".." -> read_all handle 
    |  item -> item :: read_all handle 
    | exception End_of_file -> []


let d  = Unix.getcwd >> Unix.opendir >> read_all

let exec =
    List.filter Sys.is_directory >>
    List.concat_map (fun dir -> 
        dir 
        |> Unix.opendir
        |> read_all
        |> List.map (Filename.concat dir)) >>
    List.iter (fun file -> 
        (*if Filename.check_suffix ".cmo" file then 
            Sys.remove file*)
        print_endline file)