Program use recursion to show food chain
Source: Learn prolog now!, 2001, (course available on-line)
Program source code: food_chain.pl
is_digesting(X,Y) :- just_ate(X,Y). is_digesting(X,Y) :- just_ate(X,Z), is_digesting(Z,Y). just_ate(mosquito,blood(john)). just_ate(frog,mosquito). just_ate(stork,frog).