# Trying to break elements which are lists in a list? [closed]

I am trying to write a program which make the following:

``````?- g([2,3, [22,,9] ,4,,99],X).

X= [2,3,22,,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,,5]` I get also `[2,,5]` and I really don't understand why it does this.

• why didn't you ask at Stack Overflow? – gnat Aug 8 '13 at 14:19