OCaml: Removing duplicates from a list while maintaining order from the right -

i read this thread , find interesting.

i implement remove left function in few minutes:

(*  * remove duplicate left:  * 1 2 1 3 2 4 5 -> 1 2 3 4 5  * *) let rem_from_left lst =   let rec is_member n mlst =     match mlst     | [] -> false     | h::tl ->         begin           if h=n true           else is_member n tl         end   in   let rec loop lbuf rbuf =     match rbuf     | [] -> lbuf     | h::tl ->         begin           if is_member h lbuf loop lbuf tl           else loop (h::lbuf) rbuf         end   in   list.rev (loop [] lst) 

i know implement is_member map or hashtable make faster, in moment that's not concern.

in case of implementing remove right, can implement list.rev:

(*  * remove duplicate right:  * 1 2 1 3 2 4 5 -> 1 3 2 4 5  * *) let rem_from_right lst =   list.rev (rem_from_left (list.rev lst)) 

i'm wondering if can implement in way?

instead of accumulating values on way recursing end, can collect values on way up:

let rem_from_right lst =   let rec is_member n mlst =     match mlst     | [] -> false     | h::tl ->         begin           if h=n true           else is_member n tl         end   in   let rec loop lbuf =     match lbuf     | [] -> []     | h::tl ->         begin         let rbuf = loop tl         in           if is_member h rbuf rbuf           else h::rbuf         end   in   loop lst