appendable_nlist.ml

type 'a s = private Succ

type ('elt,'size) t =
  | [] : ('elt, 'a -> 'a) t
  | (::): 'elt * ('elt, 'z -> 'k) t -> ('elt, 'z -> 'k s) t

let rec (@): type elt low mid high.
  (elt, mid -> high) t -> (elt, low -> mid) t -> (elt, low -> high) t =
 fun l r ->
 match l with
 | [] -> r
 | a :: q -> a :: (q @ r)


let wrong x y =
   x @ y, x @ 1 :: y

let lit = [1;2]
let ok = lit @ [1], lit @ lit

let lookalike = [1] @ [2]
let wrong_2 = lookalike @ [1], lookalike @ lookalike