map in ocaml

gistfile1.ml

(* batList.ml *)

type 'a mut_list =  {
	hd: 'a; 
	mutable tl: 'a list
}

external inj : 'a mut_list -> 'a list = "%identity"

let map f = function
	| [] -> []
	| h :: t ->
		let rec loop dst = function
		| [] -> ()
		| h :: t ->
			let r = { hd = f h; tl = [] } in
			dst.tl <- inj r;
			loop r t
		in
		let r = { hd = f h; tl = [] } in
		loop r t;
		inj r