(* not in 4.01 stdlib *)
let list_of_string s =
	let rec los i acc = 
		if i >= String.length s then acc
		else let ch = String.get s i in
		los (i + 1) (ch :: acc)
	in
		List.rev @@ los 0 []
 
let permissions s = list_of_string s
	|> List.map (function 
		| '-' -> 0
		| 'r' | 'w' -> 1
		| _ -> raise @@ Invalid_argument "shit happened")
	|> List.fold_left (fun acc cur -> (acc lsl 1) lor cur) 0
 
let ss = "-rw-rw-r--"
let () = print_endline @@ string_of_int @@ permissions ss

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