Problems in section: Loops and Recursions

[geohuz]

1. Can't load unix.cma, in code:

#load "unix.cma";;

Cannot find file unix.cma.

I figured out by using "utop -I +unix",

2. Unbound constructor File, in code:

# let rec string_of_filesystem fs =
  match fs with
  | File filename -> filename ^ "\n"
  | Directory fs_list ->
      List.fold_left (^) "" (List.map string_of_filesystem fs_list);;

Error: Unbound constructor File

I can't not find a type definition for File, please somebody review the documentation and fix the errors?

Thanks!