delete first three and last three elements from list, and save it to list2 in prolog

Question

I am completely new to Prolog, but I have to do this for a homework. I have tried something like this

delete(_,[],[]).  
delete([X,Y,Z],[X,Y,Z|List],Temp) :-  
   reverse(Temp,List).

But can't figure out, how to implement second delete from reversed list. Maybe I'm doing it all wrong, I'm lost, thanks for answers.

You are not only new to Prolog but also new to SO. Before asking questions, get informed by reading [the tour](http://stackoverflow.com/tour). — false, Nov 29 '14 at 14:48
What is expected behavior if 2 < number of elements < 6, say there are 5 or 3 elements in the original list? — Sergii Dymchenko, Nov 29 '14 at 19:03
@SergeyDymchenko It's quite interesting question, i haven't thought about it, because it is not in my task. I think, it would be ok, if it threw "false" or something like that. Please understand, i don't understand prolog at all, this is my first attempt to do something in it. — kristofyk, Nov 30 '14 at 20:08

score 0 · Accepted Answer · answered Nov 29 '14 at 18:39

0

Using append:

delete([A, B, C | End], Middle, [A, B, C, X, Y, Z]) :-
    append(Middle, [X, Y, Z], End).

Test run:

?- delete([1,2,3,4,5,6,7,8], L1, L2).
L1 = [4, 5],
L2 = [1, 2, 3, 6, 7, 8] 

?- delete([1,2,3], L1, L2).
false.

answered Nov 29 '14 at 18:39

Sergii Dymchenko

1

What about `[a, b, c]`: I delete the first 3 (a,b,c) and the last 3 (a,b,c) so I get `[]`. Is it not? – false Nov 29 '14 at 18:54
@false I agree. I'll ask the OP if he cares about cases. – Sergii Dymchenko Nov 29 '14 at 18:58
@false As I answered above, i didn't think about this. But it seems your code works for me. Meanwhile i came with my solution with using only delete, but I think i'll use your code. Anyway thank you for answer. – kristofyk Nov 30 '14 at 20:21

1 Answers1