Slaying a UI Anti Pattern in ReasonML

UIPattern.re

/* 
  Slaying a UI Anti Pattern in ReasonML
  Based on Kris Jenkins original writing.
  http://blog.jenkster.com/2016/06/how-elm-slays-a-ui-antipattern.html
*/
type remoteData 'e 'a =
  | NotAsked
  | Loading
  | Failure 'e
  | Success 'a;

type user = {
  id: int,
  name: string
};

type state = {data: remoteData string (list user)};

let se = ReasonReact.stringToElement;

let fetchData () => Success [{id: 1, name: "foo"}, {id: 2, name: "bar"}];

let component = ReasonReact.reducerComponent "View";

let displayData data =>
  ReasonReact.arrayToElement (
    Array.of_list (
      List.map
        (fun {id, name} => <div key=(string_of_int id)> (se name) </div>) data
    )
  );

type action = remoteData string (list user);

/* ReasonReact.NoUpdate */
let make _ => {
  ...component,
  initialState: fun () => {data: NotAsked},
  reducer: fun action state =>
    switch action {
    | NotAsked => ReasonReact.NoUpdate /* If you skip a possible case, you will get a warning not an error */
    | Loading => ReasonReact.Update {...state, data: Loading}
    | Failure msg => ReasonReact.Update {...state, data: Failure msg}
    | Success data => ReasonReact.Update {...state, data: Success data}
    },
  render: fun {state, reduce} =>
    <div>
      (
        switch state.data {
        | NotAsked =>
          <div>
            (se "Not Data Fetched Yet!")
            <button
              onClick=(
                fun _evt => {
                  Js.Global.setTimeout (reduce (fun () => Loading)) 10;
                  Js.Global.setTimeout (reduce fetchData) 2000;
                  ignore ()
                }
              )>
              (se "Fetch Data!")
            </button>
          </div>
        | Loading => <div> (se "Loading Data...") </div>
        | Failure msg => <div> (se ("Some Error: " ^ msg)) </div>
        | Success data => <div> (se "Loaded Users") (displayData data) </div>
        }
      )
    </div>
};

I'm several months late, but in case anyone else finds their way here, you can promote warnings to errors in your bsconfig.json. For example I have this:

  "warnings": {
    "error": "+8+11"
  }

This means that warning codes 8 (missing case in pattern match) and 11 (redundant case in pattern match) are treated as errors at compile time. The full list is here