Game lab

Practice: Wordle

In this lab you will implement the logic for Wordle: a word-guessing game. Each game picks a secret five-letter word, the target. You get six guesses, each one itself a real five-letter word. After every guess, each of its five letters is colored: green if it's in the right spot, yellow if it's in the target but the wrong spot, and gray if it isn't in the target at all. Guess the target exactly, in six guesses or fewer, and you win.

This lab does not depend on the Tic-Tac-Toe or Game of Life labs. You can do it in any order, or on its own.

On the right is a game panel (hidden for now) that will render the board and let you play the game. All of the piping for the game is already in place so you will only be implementing the logic. For any problem, you can test your solution by pressing the Check button, which will run a series of tests on your code. If you get stuck, a reference solution sits collapsed under each problem.

None of it plays real Wordle yet: every guess gets scored all gray, nothing you type can win, and New Game just cycles through five fixed words. Functionality gets added as you go along and code up the functions that make the game work. The final result will be a fully playable Wordle clone.

Six small functions build the whole game: random_target picks the target; score_guess and is_win turn a guess into colored feedback and check whether it won; keyboard_hint colors the on-screen keyboard from your guess history; is_valid_guess rejects a guess that isn't a real word; and count_letter is a small helper for the stretch problem, which fixes a bug in score_guess's handling of repeated letters.

Below you can read some of the important functions and definitions that you will have to use as you code up the solutions to the given functions.

guesses here is a list of pairs, each pairing a guess with its scoring. That scoring is a letter_status array, not a list: we access it by index, and arrays handle that better than lists do. The OCaml manual covers the fuller set of differences between the two. For this game, an array behaves like a list indexed by numbers starting at 0. If scored is a letter_status array, scored.(0) reads the scoring of the guess's first letter, scored.(1) the second, and so on.

Provided: the word list

word_list holds 4,615 real five-letter English words. All valid guesses must be in this list, and the target is always picked from it.

Open the provided game code below and press Run to render the board. You need not read every function, though it is a useful example of idiomatic OCaml. The board starts with minimal functionality and gets built up as you finish the problems.

Problem 1: random_target

Pick today's target uniformly at random from an array of words.

The let () = random_target_ref := random_target line is plumbing that registers your function with the board. A similar line ends most of the problems below; you can ignore it each time.

Problem 2: score_guess, first pass

score_guess target guess scores one guess. Element i of the result describes guess.[i]: Correct if it matches target.[i] exactly, Present if that letter shows up somewhere else in target, Absent if it doesn't appear in target at all.

Problem 3: is_win

Did a scored guess win the game? All five letters Correct means yes.

Problem 4: keyboard_hint

keyboard_hint guesses ch decides what the on-screen key for letter ch should currently show, given every guess submitted so far.

Problem 5: is_valid_guess

Real Wordle only accepts a guess that's itself a real word. Right now this page accepts anything five letters long, including nonsense.

Problem 6: count_letter

A helper for the fix in the Stretch problem below.

Stretch, Hard: score_guess, fix the repeated-letter bug

Rewrite score_guess, same name as Problem 2, so score_guess "batch" "abbey" comes out [| Present; Present; Absent; Absent; Absent |] instead of Problem 2's [| Present; Present; Present; Absent; Absent |]. The rule, precisely:

• Correct: guess.[i] = target.[i]
• Present: guess.[i] occurs in target, but this occurrence isn't Correct
• Absent: guess.[i] doesn't occur in target at all, or all its occurrences are already claimed by other letters in this guess

This let REPLACES Problem 2's score_guess: once your solution above has run, every cell below it (including Problem 2's own hidden test, if it re-runs, and every problem from here on) sees this version. Nothing special makes that happen -- it's the same "later binding of the same name wins" rule this whole page already runs on, just noticed twice in a row for one function.