How to fill in predicate parameters by entering in the prolog?

Question

I have the following code:

size(5). black(1,3). black(2,3). black(3,2). black(4,3). black(5,1). black(5,5). words([do,ore,ma,lis,ur,as,po, so,pirus, oker,al,adam, ik]) . :- use_module(library(lists),[nth1/3, select/3]). crossword(Puzzle) :- words(WordList), word2chars(WordList,CharsList), make_empty_words(EmptyWords) , fill_in(CharsList,EmptyWords), word2chars(Puzzle,EmptyWords). word2chars([],[]). word2chars([Word|RestWords] ,[Chars|RestChars] ) :- atom_chars(Word,Chars), word2chars(RestWords,RestChars). fill_in([],[]). fill_in([Word|RestWords],Puzzle) :- select(Word,Puzzle,RestPuzzle), fill_in(RestWords,RestPuzzle). make_empty_words(EmptyWords) :- size(Size), make_puzzle(Size,Puzzle), findall(black(I,J),black(I,J),Blacks) , fillblacks(Blacks,Puzzle), empty_words(Puzzle,EmptyWords). make_puzzle(Size,Puzzle) :- length(Puzzle,Size), make_lines(Puzzle,Size). make_lines([],_). make_lines([L|Ls],Size) :- length(L,Size), make_lines(Ls,Size). fillblacks([],_). fillblacks([black(I,J)|Blacks],Puzzle) :- nth1(I,Puzzle,LineI), nth1(J,LineI,black), fillblacks(Blacks,Puzzle). empty_words(Puzzle,EmptyWords) :- empty_words(Puzzle,EmptyWords,TailEmptyWords), size(Size), transpose(Size,Puzzle,[],TransposedPuzzle), empty_words(TransposedPuzzle,TailEmptyWords,[] ). empty_words([],Es,Es). empty_words([L|Ls],Es,EsTail) :- empty_words_on_one_line(L,Es,Es1) , empty_words(Ls,Es1,EsTail). empty_words_on_one_line([], Tail, Tail). empty_words_on_one_line([V1,V2|L],[[V1,V2|Vars]|R],Tail) :- var(V1), var(V2), !, more_empty(L,RestL,Vars), empty_words_on_one_line(RestL,R,Tail) . empty_words_on_one_line([_| RestL],R, Tail) :- empty_words_on_one_line(RestL,R,Tail) . more_empty([],[],[]). more_empty([V|R],RestL,Vars) :- ( var(V) -> Vars = [V|RestVars], more_empty(R,RestL,RestVars) ; RestL = R, Vars = [] ). transpose(N,Puzzle,Acc,TransposedPuzzle) :- ( N == 0 -> TransposedPuzzle = Acc ; nth_elements(N,Puzzle,OneVert), M is N - 1, transpose(M,Puzzle,[OneVert|Acc], TransposedPuzzle) ). nth_elements(_,[],[]). nth_elements(N,[X|R],[NthX| S]) :- nth1(N,X,NthX), nth_elements(N,R,S). 

It is used to solve the crossword puzzle as follows:

Black squares are placed by default in the code, but I want to find a way to give black squares to the input places when I want to request a crossword puzzle.

something like that:

 black(Y1,X1). black(Y2,X2). black(Y3,X3). black(Y4,X4). black(Y5,X5). black(Y6,X6). crossword(Puzzle,Y1,X1,Y2,X2,...) :- words(WordList), word2chars(WordList,CharsList), make_empty_words(EmptyWords,Size) , fill_in(CharsList,EmptyWords), word2chars(Puzzle,EmptyWords). 

Answer 1

As @lurker mentioned, I tried to rewrite the code and give black squares as input to the program, as shown below:

 :- use_module(library(lists),[nth1/3, select/3]). crossword(Puzzle,Size,Blacks,WordList) :- word2chars(WordList,CharsList), make_empty_words(EmptyWords,Size,Blacks) , fill_in(CharsList,EmptyWords), word2chars(Puzzle,EmptyWords). word2chars([],[]). word2chars([Word|RestWords] ,[Chars|RestChars] ) :- atom_chars(Word,Chars), word2chars(RestWords,RestChars). fill_in([],[]). fill_in([Word|RestWords],Puzzle) :- select(Word,Puzzle,RestPuzzle), fill_in(RestWords,RestPuzzle). make_empty_words(EmptyWords,Size,Blacks) :- make_puzzle(Size,Puzzle), fillblacks(Blacks,Puzzle), empty_words(Puzzle,EmptyWords). make_puzzle(Size,Puzzle) :- length(Puzzle,Size), make_lines(Puzzle,Size). make_lines([],_). make_lines([L|Ls],Size) :- length(L,Size), make_lines(Ls,Size). fillblacks([],_). fillblacks([black(I,J)|Blacks],Puzzle) :- nth1(I,Puzzle,LineI), nth1(J,LineI,black), fillblacks(Blacks,Puzzle). empty_words(Puzzle,EmptyWords) :- empty_words(Puzzle,EmptyWords,TailEmptyWords), transpose(Size,Puzzle,[],TransposedPuzzle), empty_words(TransposedPuzzle,TailEmptyWords,[] ). empty_words([],Es,Es). empty_words([L|Ls],Es,EsTail) :- empty_words_on_one_line(L,Es,Es1) , empty_words(Ls,Es1,EsTail). empty_words_on_one_line([], Tail, Tail). empty_words_on_one_line([V1,V2|L],[[V1,V2|Vars]|R],Tail) :- var(V1), var(V2), !, more_empty(L,RestL,Vars), empty_words_on_one_line(RestL,R,Tail) . empty_words_on_one_line([_| RestL],R, Tail) :- empty_words_on_one_line(RestL,R,Tail) . more_empty([],[],[]). more_empty([V|R],RestL,Vars) :- ( var(V) -> Vars = [V|RestVars], more_empty(R,RestL,RestVars) ; RestL = R, Vars = [] ). transpose(N,Puzzle,Acc,TransposedPuzzle) :- ( N == 0 -> TransposedPuzzle = Acc ; nth_elements(N,Puzzle,OneVert), M is N - 1, transpose(M,Puzzle,[OneVert|Acc], TransposedPuzzle) ). nth_elements(_,[],[]). nth_elements(N,[X|R],[NthX| S]) :- nth1(N,X,NthX), nth_elements(N,R,S). 

Now, using the following input, the code returns the answer to the riddle:

 crossword(Puzzle,5,[black(1,3),black(2,3),black(3,2),black(4,3), black(5,1),black(5,5)],[do,ore,ma,lis,ur,as,pu, so,pirus, uker,al,adam, ik]). 

And the output will be:

 Puzzle = [as,pu,do,ik,ore,ma,ur,lis,adam,so,al,pirus,uker] 

Answer 2

Very nice, +1 to solve it.

In addition, I would like to show you how to use DCG to get predicates with fewer arguments for empty_words/2 and the associated predicates, which makes them easier to understand. In addition, transpose/2 already available as a library predicate in SICStus Prolog and SWI (see Its source code if you are interested in how it is implemented), so I use it instead. Please note that size/1 no longer required.

 :- use_module(library(clpfd)). % for transpose/2 in SWI-Prolog empty_words(Puzzle,EmptyWords) :- phrase(empty_words(Puzzle), EmptyWords, RestEmptyWords), transpose(Puzzle, TransposedPuzzle), phrase(empty_words(TransposedPuzzle), RestEmptyWords). empty_words([]) --> []. empty_words([L|Ls]) --> empty_words_on_one_line(L), empty_words(Ls). empty_words_on_one_line([]) --> []. empty_words_on_one_line([V1,V2|Ls0]) --> { var(V1), var(V2) }, !, [[V1,V2|Vars]], { more_empty(Ls0, Ls, Vars) }, empty_words_on_one_line(Ls) . empty_words_on_one_line([_|Ls]) --> empty_words_on_one_line(Ls). 

Other predicates remain unchanged.

Your fill_in/2 is available as permutation/2 .

maplist/2 can help you in other places, for example:

 maplist(length_list(Size), Puzzle) 

replace make_lines/2 with a short definition of length_list/2 , which I leave as a simple exercise.