mv lab 07 to 06

lectures/09/maybe_monad.ml

@@ -0,0 +1,44 @@
+type bstree = L | N of int * bstree * bstree
+
+let rec insert x t =
+  match t with
+  | L -> N (x, L, L)
+  | N (x', l, r) ->
+    if x < x' then N (x', insert x l, r)
+    else if x > x' then N (x', l, insert x r)
+    else t
+
+let of_list l = List.fold_left (Fun.flip insert) L l
+
+(* val right : bstree -> bstree option *)
+let right t =
+  match t with
+  | L -> None
+  | N (_, _, r) -> Some r
+
+(* val left : bstree -> bstree option *)
+let left t =
+  match t with
+  | L -> None
+  | N (_, l, _) -> Some l
+
+let right_left t =
+  match right t with
+  | None -> None
+  | Some r -> left r
+
+(* maybe monad *)
+let bind mt f =
+  match mt with
+  | None -> None
+  | Some t -> f t
+
+let ( >>= ) = bind
+
+let t = of_list [3;2;7;6;8];;
+t |> right >>= left;;
+t |> right >>= left >>= right >>= left;;
+
+let return t = Some t;;
+
+return t >>= right >>= left;;