Write a DCG that accepts strings of the form u2v where u and v are strings over the alphabet f0; 1g such that the number of 0’s in u is twice the number of 1’s in v. For example,
| ?- s([0,1,0,1,2,0,0,1,0],L). L=[];
L = [0]; no
Exercise 6.6 in Learn Prolog Now describes a street with
( ) three neighbouring houses that all have a di erent colour, namely red, blue, and green. People of di erent nationalities live in the di erent houses and they all have a di erent pet.
Leaving out all the other constraints mentioned in that exercise, write a DCG that outputs strings
[Col1,Nat1,Pet1, Col2,Nat2,Pet2, Col3,Nat3,Pet3]
satisy ng ( ), where the nationalities are english, spanish, japanese and the pets are jaguar, snail, zebra. For example,
| ?- s([red,english,snail, blue,japanese,jaguar, green,spanish,Z], []).
Z = zebra;
no
Write a DCG that given a non-negative integer Sum, accepts lists of integers 1 that add up to Sum. For example,
?- s(3,L,[]). L = [3];
L = [2,1]; L = [1,2]; L = [1,1,1]; no
It may be useful to write a predicate mkList(+Num,?List) that returns a list List of integers from Num down to 1. For example,
?- mkList(3,L). L = [3,2,1];
no
Be sure you understand how the DCG clauses translate to ordinary Prolog clauses with di erence lists.
