# Learn Effects Welcome to a (_fake_) presentation about learning effects in OCaml! {pause up} Effects are introduced by extending the `Effect.t` extensible variant. ```ocaml type _ Effect.t += Hello : unit Effect.t ``` {pause} We can write a new function to _perform_ our effect. ```ocaml let hello () = Effect.perform Hello ``` {pause up} Now it is your turn, complete this effect handler to do _something_ with the `Hello` effect! ```ocaml let custom_handler fn = let open Effect.Deep in try_with fn () { effc = (fun v -> failwith "TODO") } ```