Writing Prolog with ChatGPT

ChatGPT successfully generated a SWI Prolog program to solve a chess puzzle placing five pieces on a 4x4 board without attacks, finding all 16 solutions. The experiment suggests LLMs can effectively handle Prolog's syntax and logic for real-world constraint problems.

A few days ago https://www.johndcook.com/blog/2026/06/11/prolog-claude/ I wrote about using Claude to solve a chess puzzle by writing Prolog code. This morning I tried a similar chess puzzle https://www.johndcook.com/blog/2025/05/13/a-crowded-little-chess-puzzle/ with ChatGPT. The task is to place a queen, king, rook, bishop, and knight on a 4 by 4 chessboard so no piece attacks another. Of course there’s not a lot of market demand for solving chess puzzles, but there is demand for solving real-world problems that amount to logic puzzles. Experiments with chess puzzles suggest writing Prolog with LLM help might be pleasant. The syntax of Prolog can be a little odd, but the LLM handles that. And because Prolog has been around so long without changing much, you’d expect LLMs to be good at generating code in it. 1 I gave ChatGPT this prompt: Write a SWI Prolog program to solve the following chess puzzle. Place a queen, king, rook, bishop, and knight on a 4 by 4 chessboard so no piece attacks another. Print all solutions. It produced a file chess4.pl below that I ran with swipl -q -s chess4.pl -g solve -t halt It found all 16 solutions: Solution 1: queen=1-2 king=2-4 rook=3-1 bishop=4-3 knight=4-4 . K . N . . . B Q . . . . . R . Solution 2: queen=1-2 king=4-3 rook=2-4 bishop=3-1 knight=4-1 . R . . . . . K Q . . . . . B N ... Here’s the code. % chess4.pl % Place queen, king, rook, bishop, and knight on a 4x4 board % so that no piece attacks another. :- use module library lists . square X-Y :- between 1, 4, X , between 1, 4, Y . solve :- findall Board, solution Board , Boards , print solutions Boards, 1 , length Boards, Count , format 'Total solutions: ~d~n', Count . solution Board :- Pieces = queen, king, rook, bishop, knight , findall S, square S , Squares , place pieces Pieces, Squares, Board , safe Board . place pieces , , . place pieces Piece | Pieces , Squares, Piece-Square | Board :- select Square, Squares, RemainingSquares , place pieces Pieces, RemainingSquares, Board . safe Board :- safe Board, Board . safe , . safe Piece-Square | Rest , Board :- forall member OtherPiece-OtherSquare, Rest , non attacking Piece-Square, OtherPiece-OtherSquare, Board , safe Rest, Board . non attacking P1-S1, P2-S2, Board :- \+ attacks P1, S1, S2, Board , \+ attacks P2, S2, S1, Board . % Attack rules attacks king, X1-Y1, X2-Y2, :- X1-Y1 \= X2-Y2, DX is abs X1 - X2 , DY is abs Y1 - Y2 , DX =< 1, DY =< 1. attacks knight, X1-Y1, X2-Y2, :- DX is abs X1 - X2 , DY is abs Y1 - Y2 , DX =:= 1, DY =:= 2 ; DX =:= 2, DY =:= 1 . attacks rook, S1, S2, Board :- same rank or file S1, S2 , clear line S1, S2, Board . attacks bishop, S1, S2, Board :- same diagonal S1, S2 , clear line S1, S2, Board . attacks queen, S1, S2, Board :- same rank or file S1, S2 ; same diagonal S1, S2 , clear line S1, S2, Board . same rank or file X1-Y1, X2-Y2 :- X1 =:= X2 ; Y1 =:= Y2 . same diagonal X1-Y1, X2-Y2 :- DX is abs X1 - X2 , DY is abs Y1 - Y2 , DX =:= DY. % For sliding pieces, make sure no piece blocks the path. clear line X1-Y1, X2-Y2, Board :- step X1, X2, SX , step Y1, Y2, SY , NX is X1 + SX, NY is Y1 + SY, clear path NX-NY, X2-Y2, SX-SY, Board . clear path Target, Target, , :- . clear path X-Y, Target, SX-SY, Board :- \+ occupied X-Y, Board , NX is X + SX, NY is Y + SY, clear path NX-NY, Target, SX-SY, Board . step A, B, 0 :- A =:= B. step A, B, 1 :- B A. step A, B, -1 :- B < A. occupied Square, Board :- member -Square, Board . % Printing print solutions , . print solutions Board | Rest , N :- format 'Solution ~d:~n', N , print coordinates Board , print board Board , nl, N1 is N + 1, print solutions Rest, N1 . print coordinates Board :- member queen-Q, Board , member king-K, Board , member rook-R, Board , member bishop-B, Board , member knight-N, Board , format ' queen=~w king=~w rook=~w bishop=~w knight=~w~n', Q, K, R, B, N . print board Board :- forall between 1, 4, Row0 , Y is 5 - Row0, forall between 1, 4, X , piece at X-Y, Board, Symbol , format '~w ', Symbol , nl . piece at Square, Board, Symbol :- member Piece-Square, Board , , piece symbol Piece, Symbol . piece at , , '.' . piece symbol queen, 'Q' . piece symbol king, 'K' . piece symbol rook, 'R' . piece symbol bishop, 'B' . piece symbol knight, 'N' . 1 I’ve played around with generating Prolog and Lean this weekend, and I’ve had better results with Prolog. The problems with Lean haven’t been Lean per se but the Mathlib library. The library is frequently refactored, which makes sense for a young language, but this makes it harder to generate and debug code.