Lecture 1
Lecture 2
Lecture 3
Lecture 4
Lecture 5

List processing: different termination criteria

Define a predicate add_one(+InList,?OutList): InList is a list of integers and OutList is the list that results from adding 1 to each element of InList.

Define a predicate contains_0(?List) which succeeds of the input list List contains a 0.

The two exercises that you just did illustrate two different conditions for terminating the recursion. In the first case, recursion stops when the empty list is reached. In the second case, Prolog stops recursing down the list when it finds an an element with a certain property (in the example, the element has to be 0).

These are common termination criteria. All the predicates that you had to define in the previous section stop the recursion when the empty list is reached. The predicates trans_a_b and concatenate, which we saw in the lecture, also do so, while the predicate element_of is like contains_0 in that it stops recursion when an element with a particular property has been found.

Back to the practical session of day 3.