I’m playing with a simple char trie and I’m populating it with strings and I would like to get the original strings from the char trie data structure in a string list. I can do it with the strings function below but I don’t like my solution and wonder if the experts have any pointers or tips to improve that function - strings.

```
let uncons str =
(** string -> (char * string) option *)
let len = String.length str in
match len with
| 0 -> None
| 1 -> Some (String.get str 0, "")
| x -> Some (String.get str 0, String.sub str 1 (x - 1))
let getRemainder lst find =
(** 'a list -> ('a -> bool) -> ('a * 'a list) option *)
let rec getRemaindAux lst func =
match lst with
| [] -> None
| hd::tl ->
if (find hd)
then
Some (hd, ((fun () -> func(tl))()))
else
getRemaindAux tl (fun t -> func(hd::t)) in
getRemaindAux lst (fun t -> t)
module Trie =
struct
type trie = Trie of (char * trie) list
let empty = Trie []
let rec add tr str =
let uStr = uncons str in
match uStr with
| None -> tr
| Some (c, s) ->
let Trie lst = tr in
let ans = getRemainder lst (fun (chr, _) -> chr = c) in
match ans with
| None -> Trie ((c, (add empty s))::lst)
| Some ((_, next), rlst) -> Trie ((c, (add next s))::rlst)
let rec find tr str =
let uStr = uncons str in
match uStr with
| None -> Some tr
| Some (c, s) ->
let Trie lst = tr in
let ans = getRemainder lst (fun (chr, _) -> chr = c) in
match ans with
| None -> None
| Some ((_, next), _) -> find next s
let rec display tr =
let Trie lst = tr in
List.iter (fun (chr, nxt) -> print_char chr; display nxt) lst
let strings tr =
(** return original strings *)
let lsts = ref [] in
let rec stringsAux tr str =
let Trie lst = tr in
match lst with
| [] -> ()
| (chr, nxt)::tl ->
stringsAux (Trie tl) str;
let Trie nl = nxt in
let s = (str ^ String.make 1 chr) in
match nl with
| [] -> lsts := s::(!lsts)
| _ -> stringsAux nxt s
in
stringsAux tr ""; List.sort compare (!lsts)
end
let trie =
List.fold_left
(fun a b -> Trie.add a b)
Trie.empty
[
"G4143\n";
"This is the first\n";
"This is the second\n";
"This is the third\n";
"This is the fourth\n";
"That will do\n";
"Here it ends...\n";
]
let () = Trie.display trie
let () = List.iter (fun _ -> print_newline()) [1;2;]
let strs = Trie.strings trie
let () = List.iter (fun s -> print_string s) strs
```