This is an implementation of the Wordle game written in GNU Prolog. The program tries to guess English or German words and expects updates to the knowledge base about the answers. So it can help you to play a Wordle game (try https://gridgames.app/gridwords/ for Austrian/German words).
Start by consulting the code:
| ?- [wordle].
compiling /Users/stm/prolog-wordle/wordle.pro for byte code...
/Users/stm/prolog-wordle/wordle.pro compiled, 235 lines read - 15126 bytes written, 7 ms
Initialize a new game by calling the play goal with the language to use as parameter. This will load the known words from a file. Currently only the values english and german are supported.
| ?- play(german).
You can list the possible solutions by calling the words goal:
| ?- words.
...
zwick
zwing
zwirn
zwist
zyste
4411 candidates remain.
With the provided list of German words there are more than 4000 possible solutions when the game starts and no additional facts are added to the knowledge base.
Let's start and try the word insel. Maybe this guess tells us the letters i, e and l are yellow and the letters n and s are gray. So we enter this data into the knowledge base:
| ?- yellow(i, 1), gray(n), gray(s), yellow(e, 4), yellow(l, 5).
Now we can look at the remaining possibilities:
| ?- words.
...
ylide
zeile
ziele
zielt
zille
93 candidates
Now only 93 words are left. Let's ask Prolog about the best guess:
| ?- bestguess(Words).
Words = [heilt,hielt,leiht,lieht,tilde]
The program suggests to try one of these words next. It uses the following heuristic:
- prefer words with common letters over words with rarely used letters
- prefer words with distinct letters over words with duplicate letters
Let's go for tilde. Now we might get the feedback, that t and d are gray, i and e are still only yellow but l is green. So we enter the new data into the knowledge base:
| ?- gray(t), yellow(i, 2), green(l, 3), gray(d), yellow(e, 5).
Then we check the remaining solution candidates:
| ?- words.
celli
eklig
oelig
3 candidates remain.
As you can see we are down to only 3 remaining words after two guesses.
You can also use the goal bestguess1(Word) to ask for a single (random) word out of the remaining candidates:
| ?- bestguess1(Word).
Word = oelig
In the following descriptions Position and Number must be an integer between 1 and 5 and Letter must be a single character atom.
play(Language) starts a new game. All known words for the given Language are loaded from a file and established as facts. Currently Language must be the atom english or german to load the list of words.
The goals english or german can be used as a shortcut.
green(Letter, Position) marks Letter as correct on Position.
The clause removes all words that have a different letter on the given position from the knowledge base. So effectively only words that have the letter at this position are kept in the knowledge base for subsequent searches.
yellow(Letter, Position) marks Letter as used in the solution but not on Position.
The clause removes all words from the knowledge base that either do not include Letter at all or have Letter on Position.
gray(Letter, Number) marks Letter as not used in the solution if the letter occurs Number or more times.
The goal removes all words from the knowledge base where Letter occurs Number or more times.
The parameter Number should be instantiated with 1 for a letter that is only tested once and receives the gray mark.
Number should be instantiated with 2 or a higher number to remove all words where the letter occurs more than the given number. This is needed if you try a word where a specific letter is used multiple times and the result shows different colors for the letter (e.g. once yellow and once gray).
words prints a list of remaining words to the terminal.
bestguess(Words) instantiates Words with a list of words that remain as solution candidates. It uses a heuristic that prefers words with common letters.
bestguess1(Word) instantiates Word with a single random word that remain as solution candidates. It uses bestguess(Words) to produce a list of words and selects a random word from that list.
You can compile the program into a native executable using the GNU Prolog compiler:
gplc wordle.pro