Trying to break elements which are lists in a list? [closed]
https://softwareengineering.stackexchange.com/questions/207637
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29-09-2020 - |
Question
I am trying to write a program which make the following:
?- g([2,3, [22,[3],9] ,4,[5],99],X).
X= [2,3,22,[3],9 ,4,5,99]
so it searches for lists in the given list and replace it by their elements without brackets [].
so I wrote this program:
The first block just searches for the first element in the list which is list
If there is no such element it returns [there_is_no_list]
.
first_list_in_the_list([],[there_is_no_list]):-!.
first_list_in_the_list([H|_],X):-is_list(H),X=H,!.
first_list_in_the_list([_|T],X):-first_list_in_the_list(T,X).
The first block works in prolog perfectly.
The second block just search in the list for an element X and then split the list into a two lists one is the list of all elements before X and the second is the elements after X.
splite_when_find_element([H|T],H,[],T):-!.
splite_when_find_element([H|T],X,F,G):-
splite_when_find_element(T,X,F1,G),append([H],F1,F).
it also works fine in Prolog.
and the third block is append, and it joins two list together in a new list.
append([],L,L).
append([H|T],L,[H|U1]):- append(T,L,U1).
and the last part is:
gg(L,L):-first_list_in_the_list(L,[there_is_no_list]),!.
gg(L,U):-first_list_in_the_list(L,X),
splite_when_find_element(L,X,F,G),gg(G,R),append(F,X,E),
append(E,R,U).
when I give a query [2,[3],5]
I get also [2,[3],5]
and I really don't understand why it does this.
Solution
Your logic is flawed. Your first_list_in_the_list function looks for an empty list or a list with more than one element. The one element list gets ignored.