Hangman Game in SWI Prolog

Question

I'm trying to make a simple hangman game in SWI Prolog.
Since we made this program run can you help me enchance the program with the following:

1) By keeping up with the letters that have been guessed so far. If the user guesses a letter that has already been guessed, the program should say 'You guessed that!' and just continue the game.

2) Lastly, add a counter that counts the number of incorrect guesses and quits the game when a certain number is reached. The program should tell the user that they lose, display what the phrase really was, and terminate. Duplicate guesses should not be counted as wrong.

I would like to thank everyone who helped me so far. This means a lot to me.

I provide you with the code and comments.

% This top-level predicate runs the game.  It prints a 
% welcome message, picks a phrase, and calls getGuess.

% Ans = Answer
% AnsList = AnswerList

hangman:- 
    getPhrase(Ans), 
    !, 
    write('Welcome to hangman.'),
    nl,
    name(Ans,AnsList), 
    makeBlanks(AnsList, BlankList), 
    getGuess(AnsList,BlankList).

% Randomly returns a phrase from the list of possibilities.

getPhrase(Ans):-
    phrases(L), 
    length(L, X), 
    R is random(X), 
    N is R+1, 
    getNth(L, N, Ans).

% Possible phrases to guess.

phrases(['a_picture_is_worth_a_thousand_words','one_for_the_money','dead_or_alive','computer_science']).

% Asks the user for a letter guess.  Starts by writing the 
% current "display phrase" with blanks, then asks for a guess and
% calls process on the guess.

getGuess(AnsList, BlankList):- 
    name(BlankName, BlankList), 
    write(BlankName), 
    nl,  
    write('Enter your guess, followed by a period and return.'), 
    nl, 
    read(Guess),
    !, 
    name(Guess, [GuessName]), 
    processGuess(AnsList,BlankList,GuessName).

% Process guess takes a list of codes representing the answer, a list of codes representing the current
% "display phrase" with blanks in it, and the code of the letter that was just guessed.  If the guess
% was right, call substitute to put the letter in the display phrase and check for a win.  Otherwise, just
% get another guess from the user.

processGuess(AnsList,BlankList,GuessName):- 
    member(GuessName,AnsList), 
    !,
    write('Correct!'),
    nl, 
    substitute(AnsList, BlankList, GuessName, NewBlanks), 
    checkWin(AnsList,NewBlanks).

processGuess(AnsList, BlankList,_):-
    write('Nope!'),
    nl,
    getGuess(AnsList, BlankList).

% Check to see if the phrase is guessed.  If so, write 'You win' and if not, go back and get another guess.

checkWin(AnsList, BlankList):- 
    name(Ans, AnsList), 
    name(BlankName, BlankList), 
    BlankName = Ans, 
    !, 
    write('You win!').

checkWin(AnsList, BlankList):- 
    !,
    getGuess(AnsList, BlankList).


% getNth(L,N,E) should be true when E is the Nth element of the list L. N will always
% be at least 1.

getNth([H|T],1,H).

getNth([H|T],N,E):-
    N1 is N-1,
    getNth(T,N1,E1),
    E=E1.

% makeBlanks(AnsList, BlankList) should take an answer phrase, which is a list
% of character codes that represent the answer phrase, and return a list
% where all codes but the '_' turn into the code for '*'.  The underscores
% need to remain to show where the words start and end.  Please note that 
% both input and output lists for this predicate are lists of character codes.
% You can test your code with a query like this:
% testMakeBlanks:- name('csc_is_awesome', List), makeBlanks(List, BlankList), name(Towrite, BlankList), write(Towrite). 

makeBlanks(AnsCodes, BlankCodes) :-
  maplist(answer_blank, AnsCodes, BlankCodes).

answer_blank(Ans, Blank) :-
  Ans == 0'_ -> Blank = Ans ; Blank = 0'* .

% substitute(AnsList, BlankList, GuessName, NewBlanks) Takes character code lists AnsList and BlankList, 
% and GuessName, which is the character code for the guessed letter.  The NewBlanks should again be a 
% character code list, which puts all the guesses into the display word and keeps the *'s and _'s otherwise.
% For example, if the answer is 'csc_is_awesome' and the display is 'c*c_**_*******' and the guess is 's', the 
% new display should be 'csc_*s_***s***'.
% You can test your predicate with a query like this:
% testSubstitute:- name('csc_is_awesome', AnsList), name('c*c_**_*******', BlankList), name('s',[GuessName]), substitute(AnsList, BlankList, GuessName, NewBlanks),
%    name(Towrite, NewBlanks), write(Towrite). 

% Also, since the predicate doesn't deal directly with character codes, this should also work:
% substitute(['c','s','c'],['c','*','c'],'s',L).  L should be ['c','s','c'].

substitute(AnsCodes, BlankCodes, GuessName, NewBlanks) :-
     maplist(place_guess(GuessName), AnsCodes, BlankCodes, NewBlanks).

place_guess(Guess, Ans, Blank, Display) :-
    Guess == Ans -> Display = Ans ; Display = Blank.

CapelliC · Accepted Answer

maplist/3 & maplist/4 apply their first argument (a predicate of appropriate arity) against all elements of other arguments lists, then your makeBlanks could be:

makeBlanks(AnsCodes, BlankCodes) :-
  maplist(answer_blank, AnsCodes, BlankCodes).

answer_blank(Ans, Blank) :-
  Ans == 0'_ -> Blank = Ans ; Blank = 0'* .

and substitute:

substitute(AnsCodes, BlankCodes, GuessName, NewBlanks) :-
     maplist(place_guess(GuessName), AnsCodes, BlankCodes, NewBlanks).

place_guess(Guess, Ans, Blank, Display) :-
    Guess == Ans -> Display = Ans ; Display = Blank.

edit:

on additional requests: 1) can be solved with an additional predicate:

alreadyGuessed(Guess, AnsCodes) :-
   memberchk(Guess, AnsCodes).

while regards 2) getGuess and processGuess together make a loop, that will just terminate when no more calls happen. Remove the last rule of checkWin, add an argument as counter to keep track of failed guesses, and extend processGuess to signal failure:

processGuess(AnsList, BlankList, _, CountFailed) :-
  (   CountFailed == 5
  ->  format('Sorry, game over. You didn\'t guess (~s)~n', [AnsList])
  ;   write('Nope!'),
      CountFailed1 is CountFailed + 1,
      getGuess(AnsList, BlankList, CountFailed1)
  ).

Hangman Game in SWI Prolog

Answers (2)

Related Questions