Spotted Arrow

2018-01-15

Let’s Build a Random Quote Generator in Reason

I finally caved and tried out ReasonML over the weekend. Not because I wanted to but rather because I think ReasonML is a natural progression for web developers coming from JavaScript who want to get into functional programming (FP) using familiar syntax and libraries. If you are looking to shower your code with parenthesis, commas, and semicolons while utilizing FP features like pattern matching look no further than ReasonML. I do enjoy the terseness of Elm and the expressiveness of PureScript but I can’t get away from the elegant paradigm that React inspired. React’s component-based architecture is great and finding an FP language with React bindings that I understand is even better! In this article, I hope to fill in the gaps for those starting out and who need a few code snippets to hit the ground running on their ReasonML journey.

What You Will Need/Want

*I used OPAM **I used Reason Scripts

Step 1 Setup

After installing what you need above you can create a reason-react starter project using yarn:

yarn create react-app <app-name> --scripts-version reason-scripts

Step 2 Dependencies

You will need an external library that implements the fetch API and you will get this from bs-fetch. I think it should be called fetch-bs but what do I know 😁.

yarn add bs-fetch

Then after fetching the data, it will need to be parsed using a decoder. A decoder is a way of transforming a non-reason type into a reason type. The same idea holds for Elm and PureScript. In this case, you are taking JSON and converting it into a reason record.

yarn add bs-json

Modules are not explicitly imported into files like they are in JavaScript. Instead, the modules are automagically 🐇 🎩 imported with the filename as a namespace. However, you have to make the compiler aware of the module in order to use it. This happens in the bsconfig.json file.

"bs-dependencies": [
  "reason-react",
  "bs-jest",
  "bs-fetch",
  "bs-json"
],

Step 3 Setup Component

A basic app component is already setup for you but it doesn’t have everything you need to handle state like you expect in react. Instead you need what is called a reducerComponent along with some other boilerplate.

\[%bs.raw {|require('./app.css')|}\];

type state = { quote: string, author: string };

type action = NoOp;

let component = ReasonReact.reducerComponent("App");

let make = \_children => {
  ...component,
  initialState: () => {
    quote: "Hello, world!",
    author: "Anonymous",
  },
  reducer: (action, \_state) => {
    switch action {
    | NoOp => ReasonReact.NoUpdate;
    }
  },
  render: self =>
    <div className="App">
      <div>(ReasonReact.stringToElement(self.state.quote)) </div>
      <div>{ReasonReact.stringToElement(self.state.author)}</div>
    </div>
};

Let’s have a look at what’s familiar and not so familiar about this. There is initialState, the initial state of the component. I placed some dummy data to start. If you are using a reducerComponent you will be asked to define both state and action types. In this case, the state is simply a record of quote and author both of type string. I added a NoOp action type just to get the component working. Inside of the render function, there is self. The self variable acts as a conduit for this which reason/bucklescript/ocaml has no concept of. What stuck out the most for me was ReasonReact.stringToElement. Remember, these are bindings for react and not the full suite of tools like JSX. That is why functions exist to transform strings into an HTML text representation. If you see a variable with an underscore it means it’s not being used like _children. This helps the compiler to selectively remove data that doesn’t need to be held in memory. Take it out for a spin and see what you find in the browser.

yarn start

Step 4 Fetch Data

Now it’s about to get interesting. Next, you will fetch data. First, let’s create a function that fetches the data. I will call this function fetchQuote.

let make = \_children => {

let fetchQuote = () => {
    Js.Promise.(
      Fetch.fetch("[https://randomquoteapi.glitch.me/funny](https://randomquoteapi.glitch.me/funny)")
      |> then\_(Fetch.Response.text)
      |> then\_(text => {
          Js.log(text);
          Js.Promise.resolve();
        })
    ) |> ignore;
  };

{
  ...component,
  initialState: () => {
    quote: "Hello, world!",
    author: "Anonymous",
  },
  reducer: (action, \_state) => {
    switch action {
    | NoOp => ReasonReact.NoUpdate;
    }
  },
  didMount: (\_self) => {
    fetchQuote();
    ReasonReact.NoUpdate;
  },
  render: self =>
    <div className="App">
      <div>(ReasonReact.stringToElement(self.state.quote)) </div>
      <div>{ReasonReact.stringToElement(self.state.author)}</div>
    </div>
  }
};

Notice that I have another set of curly braces {} surrounding the function. That’s important. Here I am using reason’s Promise implementation and inside that, I have my fetch call.

let fetchQuote = () => {
    Js.Promise.(
      Fetch.fetch("[https://randomquoteapi.glitch.me/funny](https://randomquoteapi.glitch.me/funny)")
      |> then\_(Fetch.Response.text)
      |> then\_(text => {
          Js.log(text);
          Js.Promise.resolve();
        })
    ) |> ignore;
  };

I log the results to the console and resolve the Promise. Keep in mind that reason is compatible with bucklescript and you will see bucklescript helper libraries like Js.Promise and Js.log throughout reason’s documentation. You’ll notice ignore at the tail end of the Promise chain, which does nothing more than informing the compiler that nothing is being returned.

The only other thing I added was a didMount lifecycle method, which is passed self.

didMount: (\_self) => {
  fetchQuote();
  ReasonReact.NoUpdate;
},

Because self is not being used in this instance it is prepended with an underscore. I call the fetchQuote function and if all goes as planned you should see the API response in the console.

Step 5 Update Component State

In order to update component state, you need to transform this string representation of JSON into a reason record. With the help of json-bs, I mean bs-json, you can do this. The decoder will look something like this:

let parseResponse = (json: Js.Json.t) : state =>
  Json.Decode.{
    quote: field("quote", string, json),
    author: field("author", string, json)
  };

Be sure to place this underneath your state and action types. It’s pretty straight forward. Here you are converting the JSON string representation by plucking the quote and author field and placing them into a record. Next let’s parse the JSON string and update component state.

type state = { quote: string, author: string };

type action = NextQuote(state) | NoOp;

let parseResponse = (json: Js.Json.t) : state =>
  Json.Decode.{
    quote: field("quote", string, json),
    author: field("author", string, json)
  };

let component = ReasonReact.reducerComponent("App");

let make = \_children => {

let fetchQuote = (self) => {
    Js.Promise.(
      Fetch.fetch("[https://randomquoteapi.glitch.me/funny](https://randomquoteapi.glitch.me/funny)")
      |> then\_(Fetch.Response.text)
      |> then\_(text => {
          let result = parseResponse(Js.Json.parseExn(text));
          self.ReasonReact.send(NextQuote(result));
          Js.Promise.resolve();
        })
    ) |> ignore;
  };

{
  ...component,
  initialState: () => {
    quote: "Hello, world!",
    author: "Anonymous",
  },
  reducer: (action, \_state) => {
    switch action {
    | NextQuote(result) => ReasonReact.Update(result);
    | NoOp => ReasonReact.NoUpdate;
    }
  },
  didMount: (self) => {
    fetchQuote(self);
    ReasonReact.NoUpdate;
  },
  render: self =>
    <div className="App">
      <div>(ReasonReact.stringToElement(self.state.quote)) </div>
      <div>{ReasonReact.stringToElement(self.state.author)}</div>
    </div>
  }
};

What the hell is going on!? Well, to get the parsed response from the API you also need a helper function called Js.Json.parseExn.

let result = parseResponse(Js.Json.parseExn(text));

From my research, it looks as if buckscript is looking into a more streamlined way of parsing JSON. If you are reading this from the future then be thankful you do not have to deal with encoders/decoders! Any who, after parsing the JSON and making it into a record I send it back to my reducer with the action type of NextQuote.

self.ReasonReact.send(NextQuote(result));

It is an action type which takes a state type.

type action = NextQuote(state) | NoOp;

Inside of my reducer, I use the shorthand way of updating state.

| NextQuote(result) => ReasonReact.Update(result);

It’s the same as writing:

ReasonReact.Update({ quote: result.quote, author: result.author });

There is a quirk, however, and that is this line:

self.ReasonReact.send(NextQuote(result));

You have to use self.ReasonReact.send and not self.send because otherwise, you get an unbound field error. It’s one example of the weirdness of reason-react but it’s not nearly as bad as undefined is not a function so deal with it. Also, notice that I am passing self in from where the fetchQuote is called in didMount.

didMount: (self) => {
  fetchQuote(self);
  ReasonReact.NoUpdate;
},

I knew I couldn’t get anything passed you! If all works as expected you should see a new random quote in your browser on each refresh.

Step 6 Update Quote on User Click Event

Let’s add some interactivity! You will add a button that when clicked will fetch a new random quote. First, add an action type of Click.

type action = NextQuote(state) | Click | NoOp;

Next, add a button that sends a Click action to the reducer.

<div className="App">
  <div>(ReasonReact.stringToElement(self.state.quote)) </div>
  <div>{ReasonReact.stringToElement(self.state.author)}</div>
  <button onClick=(\_event => self.send(Click))>{ReasonReact.stringToElement("Fetch New Quote")}</button>
</div>

Lastly, handle the Click action in the reducer.

| Click => ReasonReact.SideEffects(fetchQuote);

Again, this is shorthand for:

| Click => ReasonReact.SideEffects(self => fetchQuote(self));

If all went well, you should see new random quote after clicking the button!

The code in all it’s glory:

[%bs.raw {|require('./app.css')|}];

type state = { quote: string, author: string };

type action = NextQuote(state) | Click | NoOp;

let parseResponse = (json: Js.Json.t) : state =>
  Json.Decode.{
    quote: field("quote", string, json),
    author: field("author", string, json)
  };

let component = ReasonReact.reducerComponent("App");

let make = \_children => {

let fetchQuote = (self) => {
    Js.Promise.(
      Fetch.fetch("[https://randomquoteapi.glitch.me/funny](https://randomquoteapi.glitch.me/funny)")
      |> then\_(Fetch.Response.text)
      |> then\_(text => {
          let result = parseResponse(Js.Json.parseExn(text));
          self.ReasonReact.send(NextQuote(result));
          Js.Promise.resolve();
        })
    ) |> ignore;
  };

{
  ...component,
  initialState: () => {
    quote: "Hello, world!",
    author: "Anonymous",
  },
  reducer: (action, \_state) => {
    switch action {
    | NextQuote(result) => ReasonReact.Update(result);
    | Click => ReasonReact.SideEffects(fetchQuote);
    | NoOp => ReasonReact.NoUpdate;
    }
  },
  didMount: (self) => {
    fetchQuote(self);
    ReasonReact.NoUpdate;
  },
  render: self =>
    <div className="App">
      <div>(ReasonReact.stringToElement(self.state.quote)) </div>
      <div>{ReasonReact.stringToElement(self.state.author)}</div>
      <button onClick=(\_event => self.send(Click))>{ReasonReact.stringToElement("Fetch New Quote")}</button>
    </div>
  }
};

Step 7 Rejoice!

Wow, you just completed your first reason/reason-react app. Now when you get around the water cooler with your co-workers you will have a pretty cool story to tell! Maybe.

Summary

In this article, you learned how to create a random quote generator in reason with the reason-react UI library. Along the way you installed dependencies, utilized browser APIs, built a reason-react component with lifecycle methods, and created something completely useless 😆. I hope the code snippets above help you on your journey to learning ReasonML. And who knows, maybe it becomes the language that replaces undefined is not a function.

Source Code

https://github.com/arecvlohe/reason-react-medium-example