Turn exercise 009 into practice #2177 (#2229)

* "Pratice-009-done"

* "Done"

* Update impl.ml

* Update run.ml

* Update impl.ml

* Update ex.ml

* Update dune

* Do not touch irrelevant file

* "Update -lines added"

* "Update -Extra lines deleted"

* "Update -Extra lines deleted"

* Update ex.ml

practice/009/answer/impl.ml

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+let pack list =
+  let rec aux current acc = function
+    | [] -> []    (* Can only be reached if original list is empty *)
+    | [x] -> (x :: current) :: acc
+    | a :: (b :: _ as t) ->
+       if a = b then aux (a :: current) acc t
+       else aux [] ((a :: current) :: acc) t  in
+  List.rev (aux [] [] list);;

practice/009/answer/test/dune

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

practice/009/answer/test/run.ml

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

practice/009/dune

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

practice/009/dune-project

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+(lang dune 3.7)

practice/009/ex.ml

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+open OUnit2
+
+module type Testable = sig
+  val pack : 'a list -> 'a list list 
+end
+
+module Make(Tested: Testable) : sig val v : test end = struct
+  let v = "pack" >::: [
+    "example" >:: (fun _ ->
+      assert_equal
+        [["a"; "a"; "a"; "a"]; ["b"]; ["c"; "c"]; ["a"; "a"]; ["d"; "d"];
+         ["e"; "e"; "e"; "e"]]
+        (Tested.pack ["a"; "a"; "a"; "a"; "b"; "c"; "c"; "a"; "a"; "d"; "d"; "e"; "e"; "e"; "e"]))
+  ]
+end
+
+module Work : Testable = Work.Impl
+module Answer : Testable = Answer.Impl

practice/009/work/impl.ml

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+let pack _ = failwith "Not yet implemented"

practice/009/work/test/dune

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

practice/009/work/test/run.ml

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