Logic Programming 06-25433 Autumn 2012

Lecture 8: Processing lists in Prolog 2 This lecture shows that techniques introduced before (analysing terminating conditions and recursive programming) can be used to develop more complex procedures. This lecture include: writing procedures with one or more terminating or recursive clauses; one/all deletions - deleting one or all instances of an element from a list; the effects of matching v. unification; changing the order in which solutions are presented by changing clause order.

How to prepare   At a general level of list processing (rather than specifically in Prolog), think about how you would: Append two lists to form a third, longer list, e.g: [a,b,c], [1,2,3] → [a,b,c,1,2,3] Delete one instance of a given term from a list, e.g. delete a: [a,b,c,a,b,c,a,b,c] → [b,c,a,b,c,a,b,c] [a,b,c,a,b,c,a,b,c] → [a,b,c,b,c,a,b,c] [a,b,c,a,b,c,a,b,c] → [a,b,c,a,b,c,b,c] Delete either one or all instances of a given term from a list, e.g. delete a: [a,b,c,a,b,c,a,b,c] → [b,c,b,c,b,c] Think about how, in Prolog, you could change the order in which a given term was deleted from a list - so that the instance deepest in the list is the first to be removed: [a,b,c,a,b,c,a,b,c] → [a,b,c,a,b,c,b,c] [a,b,c,a,b,c,a,b,c] → [a,b,c,b,c,a,b,c] [a,b,c,a,b,c,a,b,c] → [b,c,a,b,c,a,b,c]

Video   Recording of the lecture (Vimeo)

Slides   If you really want the slides from the lecture ... 1 slide per page 6 slides per page but don't forget printing the slides is not the same as understanding them.

Summary   Summary and programs with commentary from the lecture

Programs from the lecture   Example 1 - length of a list Example 2 - membership of a list Example 3 - finding the nth member Example 4 - Classifying elements of a list Example 5 - Pairing elements from two lists (faulty) Example 6 - Pairing elements from two lists (corrected) Example 6 - Example 6 with extra demo code Call as pair/3 Example 7 - Delete an element from a list Example 7 - Example 7 with extra demo code Call as delete_1/3 Example 8 - Delete only one element from a list Example 9 - Delete all instances of an element from a list Example 10 - Matching instead of unification Call as delete_1/3 Example 10 - Delete only one element from a list With the order of clauses reversed Example 10 - Example 11 with extra demo code With the order of clauses reversed Call as delete_1/3

Individual study suggestions and further reading   Amongst the less elementary topics on lists to be studied include: multiple uses of procedures; determinism and equality in list processing. Less elementary topics in list processing are covered in: Clocksin & Mellish. Chapter 3, sections 3.7-3.8, pp 62-68. Covington. Chapter 3, sections 3.10-3.11, pp 77-79; Chapter 7, sections 7.6, pp 182-183. Sterling & Shapiro. Chapter 7, pp 129-147. The best source on advanced list processing techniques (i.e. beyond the scope of this lecture) is: O'Keefe. Chapters 4, 5 & 6, pp 113-259.

Assessed work associated with this lecture   Tutorial sheet 4