Hi I have to solve a problem in Prolog, that sounds like this: deletes all the sublists of a list that are increasing. For example the list [1,[2],[3,4],6] becomes [1,6]. So far I have tried this but it's not working. Any help please ?
domains
el=integer
list=el*
element=integer;list
lista=element*
goal
elim([1,[2],[3],4)],L),
write(L).
predicates
elim(lista,lista)
is_increasing(lista)
is_list(lista)
clauses
is_increasing([A,B|T]) :-
B>A,
is_increasing([B|T]).
is_list([_|_]).
is_list([]).
elim([],[]).
elim([E|Es],[E|Ts]) :-
is_list(E),
is_increasing(E),
elim(Es, Ts).
attempt to modularize your code: first write an is_increasing/1. Since it appears that a list of 1 element is increasing, you can do as simply as
is_increasing([A,B|T]) :- B > A, is_increasing([B|T]).
is_increasing([_]).
then you can use it to discard elements while copying . Beware to check that an element is a list before calling. Here is a possible definition
is_list([_|_]).
is_list([]).
edit
there is a bad declaration, as advised by mbratch
element=i(integer);l(list)
should be
element=integer;list
Also, you forgot is_increasing([_]).
, and anyway you're not using at all is_list or is_increasing.
The rule eliminating sublists of course should read
elim([E|Es], Ts) :- is_list(E), is_increasing(E), elim(Es, Ts).
just add the base case and a copy. ie elim is a 3 clauses predicate...
edit apart the rule above, you need only a base case
elim([],[]).
and a copy
elim([E|Es],[E|Ts]) :- elim(Es, Ts).
just try to understand why the order of rules is also important in Prolog...
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.