wfc in clingo?

wfc.lp

% Default
#const n = 5.

% define?
cell(1..n, 1..n).

pattern(a).
pattern(b).

dx(0, 1).
dx(1, 0).
dx(I, J) :- dx(-I, -J).

legal(0, 0, P, P) :- pattern(P).

legal(0, 1, a, b).
legal(0, 1, b, a).

legal(1, 0, a, b).
legal(1, 0, b, a).

legal(DX, DY, P1, P2) :- legal(-DX, -DY, P2, P1).

adj(X1, Y1, X2, Y2, DX, DY) :-
  assign(X1, Y1, P1), assign(X2, Y2, P2),
  dx(DX, DY), |X1 - X2|==DX, |Y1 - Y2|==DY.
  
% generate?
1 { assign(X,Y,P):pattern(P) } 1 :- cell(X,Y).

% constraint?
:- adj(X1,Y1,X2,Y2,DX,DY), assign(X1,Y1,P1),
  not 1 { assign(X2,Y2,P2):legal(DX,DY,P1,P2) }.
  
#show assign/3.