Parsing and unparsing has super-linear runtime about libdash HOT 6 OPEN

parse_tilde acc = 
  let ret = if acc = [] then None else Some (implode acc) in
  function
  | [] -> (ret , [])
  ...
  | c::s' -> parse_tilde (acc @ [c]) s'  

let implode l =
  let s = Bytes.create (List.length l) in
  let rec imp i l =
    match l with
    | []  -> ()
    | (c::l) -> (Bytes.set s i c; imp (i+1) l)
  in
  imp 0 l;
  Printf.printf "implode created: %s\n" s;
  Bytes.unsafe_to_string s

/pash/compiler/parser# echo "~lovecraft" | ./parse_to_json.native
implode created: l
implode created: lo
implode created: lov
implode created: love
implode created: lovec
implode created: lovecr
implode created: lovecra
implode created: lovecraf
implode created: lovecraft
["Command",[1,[],[[["T",["Some","lovecraft"]]]],[]]]

and maybe_implode_rev acc =
  if acc = [] then None else Some (implode (List.rev acc))

and parse_tilde acc =
  function
  | [] -> (maybe_implode_rev acc, [])
  (* CTLESC *)
  | '\129'::_ as s -> None, s
  (* CTLQUOTEMARK *)
  | '\136'::_ as s -> None, s
  (* terminal: CTLENDVAR, /, : *)
  | '\131'::_ as s -> maybe_implode_rev acc, s
  | ':'::_ as s -> maybe_implode_rev acc, s
  | '/'::_ as s -> maybe_implode_rev acc, s
  (* ordinary char *)
  (* TODO 2019-01-03 only characters from the portable character set *)
  | c::s' -> parse_tilde (c :: acc) s'

and to_assign v = function
  | [] -> failwith ("Never found an '=' sign in assignment, got " ^ implode (List.rev v))
  | C '=' :: a -> (implode (List.rev v),a)
  | C c :: a -> to_assign (c :: v) a
  | _ -> failwith "Unexpected special character in assignment"