A wrapper for React's useReducer() hook that applies middleware. Written in OCaml.

client_react.ml

let use_reducer ?(middleware=[]) reducer initial =
  (* [middlewared_dispatch] is setup as a reference so we can change it to the
     dispatch function returned by [useReducer]. This way we can insert 
     middleware before the real reducer function runs. *)
  let middlewared_dispatch = React.useRef (fun a ->
    Js.Console.error2 "Dispatch called before reducer hook initialized." a)
  in

  let apply_middleware middleware state action =
    let dispatch = React.Ref.current middlewared_dispatch in

    let rec apply action = function
      | [] -> action
      | hd :: tl -> 
        match hd ~dispatch state action with
        | `Rerun a -> apply a middleware
        | `Next a -> apply a tl
        | `Stop a -> a
    in

    apply action middleware
  in

  let middlewared_reducer state action = 
    action
    |> apply_middleware middleware state
    |> reducer state
  in

  let state, dispatch = React.useReducer middlewared_reducer initial in
  React.Ref.setCurrent middlewared_dispatch dispatch;

  (state, dispatch)