mv lab 07 to 06

lectures/09/arithmetic.ml

@@ -0,0 +1,39 @@
+(* monad, mx means monad x *)
+let (>>=) mx f =
+  match mx with
+  | None -> None
+  | Some x -> f x
+
+let return x = Some x
+
+let (/) a b =
+  if b = 0 then None
+  else Some (a / b)
+
+let square x = x * x
+let square' mx = mx >>= fun x -> return (square x)
+
+let (<$>) f mx =
+  match mx with
+  | None -> None
+  | Some x -> Some (f x)
+
+(* functor *)
+let lift f mx = f <$> mx
+
+let (<*>) mf mx =
+  match mf with
+  | None -> None
+  | Some f -> f <$> mx
+
+let add a b = a + b;;
+
+add <$> 4 / 2 <*> Some 1
+
+let lift' f mx my = f <$> mx <*> my
+
+let ( + ) = lift' Stdlib.( + );;
+let ( - ) = lift' Stdlib.( - );;
+let ( * ) = lift' Stdlib.( * );;
+
+Some 1 + (4 / 2) = Some 3;;