Define the functions in prolog

[aznxhung]

The whole question is define the following predicates in prolog:
1, lastelem(L,X) which is true only when X is the last element in the list L.

2, replast(L,X,M) which is true only when M is the same as L except(possibly) for the last element which is X for M.

3, exchfal(L,M) which is true only when M is the same as L except that the first element of L is the last element of M and vice versa. If either L or M is empty or has length 1, then they should be equal.

Here is a samle session:
| ?-lastelem([1,2,3,4],X).
X = 4 ?;
no

| ?-replast([1,2,3,4],5,Z)
Z =[1,2,3,5] ? ;
no

| ?-exchfal([1,2,3,4],U)
U =[4,2,3,1] ?;
no

| ?-exchfal([1,2,3,4,10],U)
U =[10,2,3,4,1] ? ;
no

 

[pimi]

Hello. No.1 is easy.

lastelem([X], X).
lastelem([_|R], X) :- lastelem(R, X).

 

[pimi]

No2 is ...

%% program %%%

replast([], _, []).
replast([L], X, [X]) :- !.
replast([L1|LS], X, [L1|M]) :- replast(LS, X, M).

%%% sample %%%

?- replast([10, 20, 30], 90, M).
M = [10,20,90] ;
no

?- replast([10], 90, M).
M = [90] ;
no

?- replast([], 90, M).
M = '[]' ;
no

?- replast([10, 20, 30], X, [10, 20, 90]).
X = 90 ;
no

?- replast(X, 90, [10, 20, 90]).
X = [10,20,H120] ;
no

 

[pimi]

And No.3 is ...

exchfal([], []).
exchfal([L1|LS], [W1|W2]) :-
lastelem([L1|LS], W1),
replast(LS, L1, W2).