Regard with @nojb’s answer, you might also use to_seq
of_seq
to convert between them
let sort s =
String.to_seq s |> List.of_seq |> List.sort Char.compare |> List.to_seq |> String.of_seq;;
let sort s =
let a = s |> String.to_seq |> Array.of_seq in
Array.sort Char.compare a;
a |> Array.to_seq |> String.of_seq;;