7.3 Exercises
Exercise 7.1 Suppose we are working with the following DCG:
foo --> [choo].
foo --> foo,foo.
bar --> mar,zar.
mar --> me,my.
me --> [i].
my --> [am].
zar --> blar,car.
blar --> [a].
car --> [train].
wiggle --> [toot].
wiggle --> wiggle,wiggle.
Write down the ordinary Prolog rules that correspond to these DCG rules. What are the first three responses that Prolog gives to the query s(X,[]) ?
Exercise 7.2 The formal language a n b n −{ ϵ } consists of all the strings in a n b n except the empty string. Write a DCG that generates this language.
Exercise 7.3 Let a n b 2 n be the formal language which contains all strings of the following form: an unbroken block of a s of length n followed by an unbroken block of b s of length 2n , and nothing else. For example, abb , aabbbb , and aaabbbbbb belong to a n b 2 n , and so does the empty string. Write a DCG that generates this language.
