Last Element
Find the last element of a list. Usage example: ?-
my_last(X,[a,b,c,d]).
X = d
Implementation:%base case, if list consist of
only one element%
my_last(X, [X]) :- !.
%other cases, else remove
the head of the list and try the tail%
my_last(X, [_|T]) :-
my_last(X,T).
Second to Last Element
Find the last but one
element of a list. Assume that the list provided contains two or more
elements. Usage example: ?-
second_to_last(X,[a,b,c,d]).
X = c
Implementation:%base case,
list contains 2 elements%
%use built-in function "length"%
second_to_last(X,
[X|T]) :- length(T, 1), !.
%other case, list contains 3 or more
elements, try tail.%
second_to_last(X, [_|T]) :- second_to_last(X,
T).
Kth to Last ElementFind the K'th element of
a list. The first element in the list is number 1. Usage example: ?-
element_at(X,[a,b,c,d,e],3).
X = c
Implementation:%base case,
the element is at position 1, the head of the list%
element_at(X,[X|_],1)
:- !.
%given a list and position K>1, this predicate will iterate
past the first K-1 times in the list%
element_at(X, [H|T], K) :- N
is K-1, element_at(X, T, N).
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