portable:ocamlftvb dan$ ls
README.md _build    lib       lib_test  lwt
portable:ocamlftvb dan$ ls -l lib/
total 24
-rw-r--r--  1 dan  staff   754 29 Mar 17:53 ch3.ml
-rw-r--r--  1 dan  staff  2641  7 Apr 13:58 ch4.ml
-rw-r--r--  1 dan  staff  1984  7 Apr 15:19 ch5.ml
portable:ocamlftvb dan$ corebuild lib/ch5.native
+ ocamlfind ocamlc -c -w A-4-33-40-41-42-43-34-44 -strict-sequence -g -bin-annot -short-paths -thread -package core -ppx 'ppx-jane -as-ppx' -I lib -o lib/ch5.cmo lib/ch5.ml
File "lib/ch5.ml", line 94, characters 17-21:
Error: Unbound value take
Command exited with code 2.
Compilation unsuccessful after building 2 targets (1 cached) in 00:00:00.
portable:ocamlftvb dan$ cat lib/ch
ch3.ml  ch4.ml  ch5.ml
portable:ocamlftvb dan$ cat lib/ch5.ml
(* examples and exercises from chapter 5  *)

(* we start with an implementation of the
 * insertionsort algorithmn *)

let rec insert (e : int) (l : int list) =
  match l with
  | [] -> [e]
  | hd :: tl ->
      if e <= hd then
        e :: hd :: tl
      else
        hd :: insert e tl
let rec sort l =
  match l with
  | [] -> []
  | hd :: tl -> insert hd (sort tl)

(* so the time insertionsort above takes to complete
* can be improved with the mergesort algo below *)

(* let's start with the merge part *)

let rec merge x y =
  match x, y with
  | [], l -> l
  | l , [] -> l
  | hx :: tx, hy :: ty ->
      if hx < hy then
        hx :: merge tx (hy :: ty)
      else
        hy :: merge (hx :: tx) ty

(* now the msort part *)
let rec msort l =
  match l with
  | [] -> []
  | [x] -> [x]
  | _ ->
      let left = take (length l / 2) l in
      let rigth = drop (length l / 2) l in
      merge (msort left) (msort rigth)
portable:ocamlftvb dan$