1 Artificial Intelligence CS370D Prolog programming List operations.

Outline: List operations: - Membership. - Appending. - Reversing. - Select predicate. - Deleting an item from list. - Length of a list. 2

3 Membership operation: A common predicate when manipulating lists is a membership test: Is a given value a member of a list? The member built-in predicate takes two arguments. If the first argument is any term except a variable and the second argument is a list. If the first argument is an variable, it is bound to an element of the list working to find all the elements of a list in turn from left to right. member succeeds if the first argument is a member of the list denoted by the second argument (i.e. one of its list elements).

4 Membership operation examples: Examples: ?-member(maha, [laila,maha,sara]). true ?- member(dog, [cat,[dog,horse]]). false ?- member([apple,orange], [banana,[apple,orange]]). true ?- member(x,[]). false ?- member([1,2,3],[a,b,[1,2,3],c]). true ?- member(X,[a,b,c]). X =a ;X = b ;X = c.

5 Append operation: The append built-in predicate takes three arguments: append(L1,L2,L3). - If the first two arguments L1,L2 are lists and the third argument is an variable, the third argument is bound to a list comprising the first two lists concatenated. - If the all arguments are lists, then the predicate check if the last argument L3 contains all element of L1 and L2 and then return true or false. - If the first two arguments are variables and the last argument is a list then try to divide the list between these variables.

6 Append operation examples: Examples: ?- append([1,2,3,4],[5,6,7,8,9],L). L = [1,2,3,4,5,6,7,8,9] ?- append([],[1,2,3],L). L = [1,2,3] ?- append([[a,b,c],d,e,f],[g,h,[i,j,k]],L). L = [[a,b,c],d,e,f,g,h,[i,j,k]]

7 Append operation examples: (cont) Examples: ?- append([a,b],[c,d],[a,b,c,d]). yes ?- append([a,b],[c,d],[a,b,a,c,d]). no ?- append([],[b,c],[b,c,d]). no ?-append([a,[b,c],d],[a,b],L). L = [a, [b, c], d, a,b].

8 Append operation examples: (cont) Examples: ?- append(L1,L2,[1,2,3]). L1 = [],L2 = [1,2,3] ; default L1 = [1],L2 = [2,3] ; L1 = [1,2],L2 = [3] ; L1 = [1,2,3],L2 = []. ?- L = [1,2,3,4,5], append(L1,[_,_,_],L). L = [1, 2, 3, 4, 5], L1 = [1, 2]

9 Reversing a list: The term reverse the elements in L1 and put them reversed in L2 variable: reverse(L1,L2). If all arguments are lists then check if the second argument reversed from the first then return true of false. reverse(List1,List2).

10 Reversing a list: Examples: ?- reverse([1,2,3,4], What). What=[4,3,2,1] ?- reverse([a,b,c],[c,b,a]). true

11 Select predicate: This predicate check if L2 has the same items in L1 after element removed as the same order. select(element,L1,L2). Examples: ?- select(a,[a,c],[a,d]). false. ?- select(1,[1,2,3],[3,2]). false. Not the same order. ?- select(a,[a,b,c],[b,c]). true. ?- select(a,[b,c],[b,c]). false. The first list does not contain the item.

12 Delete item from list: The term delete the element fromL1 where L2 is equal to L1 with the item X removed delete(L1, element,L2). Examples: ?- delete([a,b,c],a,L). L = [b, c]. ?- delete([a,b,c],g,H). H = [a, b, c]. ?- delete([a,b,a,a],a,L). L = [b].

13 Length of a list: length (List, N) This term used to count the elements in a list List and put the numbers in the N variable. Examples: ?- length([a,b,c],N). N = 3 ?- length([],M). M = 0. ?- length([a,b,c],5). False.

14 Reference: More predicates of SWI prolog lists can found here: