Added new functions and summary at beginning

Lists.pro

@@ -1,3 +1,36 @@
+% =====================================
+% Operations on Lists:
+% 
+% Iterators:
+% - iter
+% - iter_rev
+% - iter_every_2nd
+% - iter_nth
+% - iter_odd
+% - iter_even
+% 
+% Metadata:
+% - len
+% - count (occurances of element)
+% - indexof
+% - sum (sum list of integers)
+% - member (test if a element is in a list)
+% 
+% Manipulation/Access:
+% - nth (get N-th element) 
+% - remove (remove element by value)
+% - del (remove element at index)
+% - del_last
+% - del_first
+% - insert (insert at index)
+% - add (append)
+% - merge
+% - repeat 
+% 
+% =====================================
+
+% what to do on each iteration
+do_sth(X):-writeln(X).
 
 % iterate over list in sucessive order
 % prints each element
@@ -5,19 +38,19 @@
 % example: iter_nth([1,2,3,4,5,6,7,8,9])
 % output: [1,2,3,4,5,6,7,8,9]
 iter([]).
-iter([H|T]):-writeln(H), iter(T).
+iter([H|T]):-do_sth(H), iter(T).
 
 % iterate over list in reverse order
 % prints each element
 %
 % example: iter_nth([1,2,3,4,5,6,7,8,9])
 % output: [9,8,7,6,5,4,3,2,1]
-iter_rev([A]):-writeln(A).
-iter_rev([H|T]):-iter_rev(T), writeln(H).
+iter_rev([A]):-do_sth(A).
+iter_rev([H|T]):-iter_rev(T), do_sth(H).
 
 % prints every 2nd element from the supplied list
 iter_every_2nd([]).
-iter_every_2nd([_|[H2|T]]):-writeln(H2), iter_every_2nd(T).
+iter_every_2nd([_|[H2|T]]):-do_sth(H2), iter_every_2nd(T).
 
 % iterate over every nth element in the list
 %
@@ -27,7 +60,7 @@ iter_nth([], _, _).
 iter_nth([H|T], E, 0):-
     R is E - 1,
     iter_nth(T, E, R),
-    writeln(H).
+    do_sth(H).
 
 iter_nth([_|T], E, L):-
     R is L - 1,
@@ -83,7 +116,7 @@ nth([_|T], C, O):-
 %
 % example: indexof([0,1,3,4,5,6,7,8,9], 3, X)
 % output: X = 2
-indexof([],_,C):-C is 0.
+indexof([],_,_).
 indexof([H|_],E,C):-
     H == E,
     C is 0.
@@ -91,3 +124,93 @@ indexof([_|T],E,C):-
     indexof(T,E,R),
     C is R + 1.
 
+% removes all elements of Tar from the list
+%
+% example: remove([a,b,c,d], a, X)
+% output: X = [b,c,d]
+remove([],_,[]).
+remove([Head|Tail], Head, Res):-
+    remove(Tail, Head, Res).
+remove([Head|Tail], Tar, [Head|Res]):-
+    remove(Tail, Tar, Res).
+
+% removes the last element
+%
+% example: del_last([1,2,3,4], X)
+% output: X = [1, 2, 3]
+del_last(List, Res):-
+    len(List, Len),
+    Tmp is Len - 1,
+    del(List, Tmp, Res).
+
+% removes the first element
+%
+% example: del_first([1,2,3,4], X)
+% output: X = [2, 3, 4]
+del_first([_|Tail], Tail).
+
+% append an element to the right end of the list
+%
+% example: add([a,b,c,d], a, X)
+% output: X = [a,b,c,d,a]
+add([], Elem, [Elem]).
+add([Head|Tail], Elem, [Head|Tail2]):-
+    add(Tail, Elem, Tail2).
+
+% insert an element into the list at a certain index
+%
+% example: insert([a,b,c,d], k, 2, X)
+% output: X = [a, b, k, c, d]
+insert([], _, _, []).
+insert([Head|Tail], Elem, 0, [Elem|[Head|Tail]]).
+insert([Head|Tail], Elem, Idx, [Head|Res]):-
+    Idx2 is Idx - 1,
+    insert(Tail, Elem, Idx2, Res).
+
+% remove an element at the specified index from the list
+%
+% example: del([a,b,c,d], 2, X)
+% output: X = [a, b, d]
+del([], _, _, []).
+del([_|Tail], 0, Tail).
+del([Head|Tail], Idx, [Head|Res]):-
+    Idx2 is Idx - 1,
+    del(Tail, Idx2, Res).    
+
+% merge to lists together
+%
+% example: merge([a,b], [3,4], X)
+% output: X = [a, b, 3, 4]
+merge(List, [], List).
+merge(List,[Head|Tail],Res):-
+    add(List, Head, Tmp),
+    merge(Tmp, Tail, Res).    
+
+% sum a list of values
+%
+% example: sum([1,2,3,4], X)
+% value: X = 10
+sum([], 0).
+sum([Head|Tail], Res):-
+    sum(Tail, Tmp),
+    Res is Tmp + Head.
+
+% detect whether an elemenz is part of a given list
+%
+% example: member([1,2,3,4], 4)
+% output: true
+%
+% example: member([1,2,3,4], 9)
+% output: false
+member([Elem|_], Elem).
+member([_|Tail], Elem):-member(Tail, Elem).
+
+% repeat sth N-times
+%
+% example: repeat(a, 5, X).
+% output: X = [a,a,a,a,a]
+repeat(_, 0, []).
+repeat(Elem, N, [Elem|Tmp]):-
+    N1 is N - 1,
+    repeat(Elem, N1, Tmp).
+