Turn exercise 023 to practice

practice/023/answer/impl.ml

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+let rand_select list n =
+  let rec extract acc n = function
+    | [] -> raise Not_found
+    | h :: t -> if n = 0 then (h, acc @ t) else extract (h :: acc) (n - 1) t
+  in
+  let extract_rand list len =
+    extract [] (Random.int len) list
+  in
+  let rec aux n acc list len =
+    if n = 0 then acc else
+      let picked, rest = extract_rand list len in
+      aux (n - 1) (picked :: acc) rest (len - 1)
+  in
+  let len = List.length list in
+    aux (min n len) [] list len
+

practice/023/answer/test/dune

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+(include_subdirs no)
+(test (name run) (libraries ounit2 ex))

practice/023/answer/test/run.ml

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+module Test = Ex.Make(Ex.Answer)
+
+let () = OUnit2.run_test_tt_main Test.v

practice/023/dune

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+(include_subdirs qualified)
+(library (name ex) (libraries ounit2))

practice/023/dune-project

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+(lang dune 3.7)

practice/023/ex.ml

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+open OUnit2
+
+module type Testable = sig
+  val rand_select : 'a list -> int -> 'a list
+end
+
+module Make(Tested: Testable) : sig val v : test end = struct
+  let v = "rand_select" >::: [
+    "nil" >:: (fun _ -> assert_equal [] (Tested.rand_select [] 0));
+    "cons" >:: (fun _ -> assert_equal ["e"; "c"; "g"] (Tested.rand_select ["a"; "b"; "c"; "d"; "e"; "f"; "g"; "h"] 6));
+  ]
+end
+
+module Work : Testable = Work.Impl
+module Answer : Testable = Answer.Impl

practice/023/work/impl.ml

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+let rand_select _ = failwith "Not yet implemented"

practice/023/work/test/dune

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+(include_subdirs no)
+(test (name run) (libraries ounit2 ex))

practice/023/work/test/run.ml

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+module Test = Ex.Make(Ex.Work)
+
+let () = OUnit2.run_test_tt_main Test.v