Using Conc for more list functions

We can write a procedure for deleting elements from within a list

delete( X, List, Result) :-
 conc( L1, [X| L2], List),
 conc( L1, L2, Result).

• To delete X from list, X should be found as the head of the second (or right) part of the List
• This partitions the list into L1 and L2
• Result is then obtained by removing X, and concatenating the remained of L2 to L1

Sample query :

 delete(2, [1,2,3,4], Result) 
 Result = [1,3,4]

Similarly, one can insert elements into the list :

 insert(X, List, Result) :-
   delete(X, Result, List).

How does this work ? Try developing the definition in terms of the conc definition earlier

It is also possible to look for an arbitrary sublist within the list, this can again be achieved by using the conc definition earlier. Hence :

sublist(List, Sublist) :-
 conc(_, L1, List),
 conc( Sublist, _, L1).

A query of the form :

sublist([1,2,3,4,5,6],[3,4,5])
yes

• Sublist works by assigning L1 to be Sublist and something else, note the use of the {anonymous variable)
• List is then constructed by combining L1 with some something else as the left part
• Sublist is therefore the left part of some right segment of List