% Example for using rational trees for grammars % Adapted from Alain Colmerauer: Prolog and infinite trees %query: q(i). q(X) :- grammar(G), terminal-string(X), produces(G,X). grammar(S) :- equal(S,or(N,and(a,and(S,b)))), equal(N,or(c,and(c,N))). equal(X,X). terminal-string(nil). terminal-string(and(A,X)) :- terminal(A), terminal-string(X). terminal(a). terminal(b). terminal(c). produces(G,X) :- gives(G,X,nil). gives(or(P,Q),X,Y) :- gives(P,X,Y). gives(or(P,Q),X,Y) :- gives(Q,X,Y). gives(and(P,Q),X,Z) :- gives(P,X,Y), gives(Q,Y,Z). gives(A,and(A,X),X) :- terminal(A).
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