Adding numbers in a List?

[Netherbeast]

Im new to this language and am having a hard time manipulating atoms in the list.

All im trying to do is add the numbers of a given list, say like add([2, 3, 4], Total).
and the Total = 9.

I can count how many elements are in the list using this code:
len([], 0).
len([CAR|CDR], X) :- len(CDR, X1), X is X1+1.

but getting it to add all the numbers is harder than I thought.

Thanks in advance

 

[LordKinbote]

Try using an accumulator to keep track of the sum so far.

add(Lst,Sum) :- add(Lst,Sum,0).

add([],Sum,Sum).
add([X|Xs],Sum,Acc) :- NewAcc is Sum+Acc,
add(Xs,Sum,NewAcc).

I haven't tested it, but this should do the trick. The add/2 rule sets the accumulating helper to start at 0. Then the helper moves through the list and adds each value to some holder called Acc. When the list is empty, it copies the value currently in Acc into Sum.