Spotted Arrow

2017-08-25

Let’s Build a Simon Game in PureScript Pt . 5 The Final Installment

To summarize, in the last post you learned how to create an animation in PureScript using the Pux architecture and some handy tools from the PureScript ecosystem. In this post, you will expand upon the previous lessons and generate an animated sequence that you can then check against user input.

This lesson will probably be the longest of all the other lessons but it will also be the final lesson so it shouldn’t be too bad 😜.

Generate A Random Sequence 🎉

The core of this game is a random series of button presses that users have to repeat in order to win. First, let’s create a button that when pressed starts the game and generates the random sequence for the user and places the sequence in state. Then you can reference that sequence later when you want to check it against user input. Hop on over to the view and add a button to start the game.

import Text.Smolder.HTML (div, button) -- Added button

\-- The other divs are above
button #! onClick (const StartGame ) $ text "Start"

As you probably noticed, StartGame is not a registered tag in your Event tagged union. Head on over to the Events.purs file and make that change.

data Event = UserClick String | ResetColor | StartGame

Now that you have the event, let’s head on over to the Update.purs file and start to think about how to generate the random sequence. Thankfully, you already have a helper built for this called generateRandoSequence which will finally come in handy ✋.

Add a new foldp function and pattern match on the StartGame event.

foldp StartGame state = onlyEffects state
  \[ do
      colors <- liftEff generateRandoSequence
      pure $ Just $ NextSequence colors
  \]

Okay, you know that that generateRandoSequence creates a side-effect of RANDOM. So you will need to update AppEffects to be aware of that type.

import Control.Monad.Eff.Random (RANDOM) -- Added

type AppEffects = (console :: CONSOLE, random :: RANDOM)

You also know that Pux only executes asynchronous effects, which is why you call liftEff on generateRandoSequence, essentially taking a synchronous effect and make it asynchronous.

import Control.Monad.Eff.Class (liftEff) -- Added

And because effects expects a Maybe Event to be returned, here you provide NextSequence with the random colors sequence. That Event, however, is not part of the tagged union. Run on over to Events.purs and fix that.

data Event
  = UserClick String
  | ResetColor
  | StartGame
  | NextSequence (List String)

You will probably get yelled at that type List is not defined. Make sure to import the List type at the top of the file.

import Data.List (List)

Let’s now handle the NextSequence event in the foldp function and update the state. Before doing this, update the State type and the init function.

type State =
  { currentColor :: String
  , sequence :: List String
  }

init :: State
init =
  { currentColor: ""
  , sequence: Nil
  }

You know that the sequence will be a List String so it’s easy to declare that type in state. But what about an empty List. Thankfully there is a type for that called Nil that you can use in the init function. To bring in Nil make sure you updated your Data.List import.

import Data.List (List(..)) -- Changed

Whoah 😅. Okay, everything is now in place to update the state after clicking the start button. Let’s add a bit more logic to the foldp function to get that going. All you have to do is pattern match on the NextSequence event and update the state.

import Control.Monad.Aff.Console (logShow) -- Added

foldp (NextSequence colors ) state =
  { state: state { sequence = colors }
  , effects: \[ logShow colors $> pure Nothing \]
  }

Just for kicks and gigs, you are logging what you have to the console so you can see the output.

At this point I think it’s safe to run pulp server and when you click the start button you should see something in your console.

Generate an Animated Sequence 🎭

Up to this point you have created a random sequence and made it part of state. What you haven’t done is make it animated. This is another core tenant of the game and once this is completed I think it will give you enough momentum to continue on and complete this project without much more assistance.

To understand what an animated sequence entails I think it’s important to first understand what a round is in the Simon game. A round consists of a series of button clicks followed by user input. The button clicks that a user inputs have to align with the same sequence as the original, otherwise the user has to start the round back again, or if in strict mode, start back at 1.

For example, if the series is: “red”, “blue”. The user has to input “red” and “blue” in that order otherwise the user starts back at 2 and this all starts over again. The kick off of a round starts after clicking the start button. Let’s create a function that given a count will animate a sequence to up to that count. This is what I came up with:

You will need some array helpers. So first install:

bower install --save purescript-arrays

Then inside of Update.purs:

\-- Added imports
import Data.Array (range, concatMap)
import Data.List (fromMaybe, index)
import Data.Int (toNumber)

generatePlaySequence :: forall e. Int -> List String -> Array (Aff e (Maybe Event))
generatePlaySequence count sequence =
  range 0 (count - 1) #
  concatMap (\\v ->
    \[ do
        delay $ Milliseconds ((toNumber v + 1.0) \* 1000.0)
        let color = fromMaybe "" $ index sequence v
        pure $ Just $ AnimateColor color
    \]
  )

How does this actually work 🤔? Good question. I have no idea 😊. Just kidding. What I am trying to do here is to create a series of effects that are delayed each by 1 second. I am using concatMap because inside of the concatMap function I have a do block inside of an array. It would be an array of arrays in the end but with concatMap you get one nice flattened array. To get the color from the List I am using fromMaybe. In case a color does not exist in that index it can be safely handled, instead of breaking the browser. And the animate effect at the end is called to actually animate the color. You already have the code for what that entails. You know the process! Add the event in the Event.purs file.

data Event
  = UserClick String
  | ResetColor
  | StartGame
  | NextSequence (List String)
  | AnimateColor String

Then add the pattern match to the foldp function.

This doesn’t quite get you to animating a sequence, yet. Do you know why? Well, first we haven’t called the generatePlaySequence function for starters. Do that inside the NextSequence pattern.

foldp (NextSequence colors ) state =
  { state: state { sequence = colors, count = state.count + 1 }
  , effects: \[ pure $ Just $ PlaySequence \]
  }

Whenever you click the start button a new sequence is created but also the count of the game begins. That’s why you add 1 to count. Oh, and by the way, update the state and init functions to reflect this new state being tracked.

type State =
  { currentColor :: String
  , sequence :: List String
  , count :: Int
  }

init :: State
init =
  { currentColor: ""
  , sequence: Nil
  , count: 0
  }

You probably also noticed that I added a new effect, PlaySequence. That can only mean two things. Update the Event.purs file and then theUpdate.purs foldp function.

data Event
  = UserClick String
  | ResetColor
  | StartGame
  | NextSequence (List String)
  | AnimateColor String
  | PlaySequence

foldp PlaySequence state = onlyEffects state (generatePlaySequence state.count state.sequence)

Given a count and the sequence, the Simon game can now actually do something when you click start. Let’s try it out. Run pulp server and see what happens when you click start.

You could either be saying, “yay!” or “gosh darn it!” at this point. When you clicked the start button a domino effect should have gone off. First a new sequence should have been created. After it’s created PlaySequence effect should have been called. At that point the count is 1 and the sequence, well, is the sequence. The function generatePlaySequence function creates a range between 0 and the count minus 1. Then creates an array of do blocks that are delayed 1 second apart. Each delay entails AnimateColor which given color makes that the currentColor, darkening it on the screen, and after 300 milliseconds, it resets. Whoah, that’s a lot! I am getting dizzy. Let’s keep going!

If you keep hitting the start button the count will continue to get bigger and you will see longer and longer sequences! The sequences will be new random sequences each time as well 😲

Tracking User Input 👩‍💻

The next phase of this post is to track user input. The reason for this is to compare the sequence and make sure the user matches that sequence to the tee. If the user does not match the sequence then the round starts over.

There is already a function that tracks user input. It’s foldp, duh! But the specific pattern is UserClick. I think an easy way to do this is with a let expression and some if/else blocks. To track user clicks it needs to be held in state somewhere. Let’s call it userClicks.

type State =
  { currentColor :: String
  , sequence :: List String
  , count :: Int
  , userClicks :: List String
  }

init :: State
init =
  { currentColor: ""
  , sequence: Nil
  , count: 0
  , userClicks: Nil
  }

Next let’s compare what the user clicks with the current sequence up to the current count of the game. You can start with happy path where user clicks equal the sequence up to that count.

foldp (UserClick color) state =
  let
    nextUserClicks = snoc state.userClicks color
    allMatch = nextUserClicks == (slice 0 (length nextUserClicks) state.sequence)
  in
    if allMatch && (length nextUserClicks) == state.count then
      { state: state { count = state.count + 1, userClicks = Nil }
      , effects:
        \[ pure $ Just $ AnimateColor color
        , pure $ Just PlaySequence
        \]
      }
    else if allMatch then
      { state: state { userClicks = nextUserClicks }
      , effects: \[ pure $ Just $ AnimateColor color \]
      }
    else
      { state: state
      , effects:
        \[ pure $ Just $ AnimateColor color
        , pure $ Just PlaySequence
        \]
      }

For each UserClick you will create what the nextUserClicks will be. If the sequence of nextUserClicks and the sequence up to that point are the same, then you know that the user has input the correct information. There is also a fork here. There is a point when the userClicks is the same length as the count and when it’s not. When it’s not, but allMatch, then you still need to pass back the nextUserClicks. When it is, you need to go to the next round. This is done with adding a new count, and resetting userClicks to Nil. Otherwise, you pass back the state and replay the sequence. Make sense? 🤔

For some more kicks and gigs let’s see this run in the browser. Run pulp server and see what you got.

Summary ✅

You should be proud. You have learned a lot over these past 5 lessons. Now take your knowledge and build out the rest of this Simon game and complete the rest of the user stories. I think I have done my best to give you the momentum to carry this project to fruition, if not, you can take it into an entirely different direction as well. Who knows, you might even write a blog post about it 😁.

Below is what you have accomplished so far and what needs to be added. I am depending on your! 😉

User Stories:

  • ̶I̶ ̶a̶m̶ ̶p̶r̶e̶s̶e̶n̶t̶e̶d̶ ̶w̶i̶t̶h̶ ̶a̶ ̶r̶a̶n̶d̶o̶m̶ ̶s̶e̶r̶i̶e̶s̶ ̶o̶f̶ ̶b̶u̶t̶t̶o̶n̶ ̶p̶r̶e̶s̶s̶e̶s̶
  • ̶E̶a̶c̶h̶ ̶t̶i̶m̶e̶ ̶I̶ ̶i̶n̶p̶u̶t̶ ̶a̶ ̶s̶e̶r̶i̶e̶s̶ ̶o̶f̶ ̶b̶u̶t̶t̶o̶n̶ ̶p̶r̶e̶s̶s̶e̶s̶ ̶c̶o̶r̶r̶e̶c̶t̶l̶y̶,̶ ̶I̶ ̶s̶e̶e̶ ̶t̶h̶e̶ ̶s̶a̶m̶e̶ ̶s̶e̶r̶i̶e̶s̶ ̶o̶f̶ ̶b̶u̶t̶t̶o̶n̶ ̶p̶r̶e̶s̶s̶e̶s̶ ̶b̶u̶t̶ ̶w̶i̶t̶h̶ ̶a̶n̶ ̶a̶d̶d̶i̶t̶i̶o̶n̶a̶l̶ ̶s̶t̶e̶p̶
  • I hear a sound that corresponds to each button when I click the button and when the series of buttons plays
  • If I press the wrong button, I am notified I have done so and ̶t̶h̶e̶ ̶s̶e̶r̶i̶e̶s̶ ̶o̶f̶ ̶b̶u̶t̶t̶o̶n̶ ̶p̶r̶e̶s̶s̶e̶s̶ ̶s̶t̶a̶r̶t̶ ̶o̶v̶e̶r̶
  • I can see how many steps are in the current series
  • If I want to restart, I can hit a button to do so, and I return to a single step
  • I can play strict mode where if I get a button press wrong, the game notifies me and the game restarts the current random series from one
  • I can win the game by getting a series of 20 steps correct. I am notified of my victory and I restart with a new random series of buttons presses

As I have said repeatedly, I recommend looking at the book PureScript by Example as well as the PureScript Documentation to get some background if you haven’t done so already. Also, check out all the library document on Pursuit. If you have any questions check out the Slack or Gitter channels. Until next time, keep hacking!

Part 5 of this project is tagged and can be found on Github here:

If you are wanting to see what a finished product looks like, check this one out: