Prolog program Write a predicate sumlists(L1, L2, L3) where L1, L2, L3 are lists

Question

Prolog program

Write a predicate sumlists(L1, L2, L3) where L1, L2, L3 are lists of integers. The predicate sumlists succeeds when L3 has a list of integers where each element is the sum of the corresponding elements from L1 and L2. For example sumlists([1,2,3], [3,4,5], L3) should return L3 = [4,6,8]. Handle the case where L1 and L2 are of different lengths (the output list L3 would have the length of the longer input list, and the elements in it after the shorter list ran out would just be equal to the elements in the longer list).

Explanation / Answer

list_sum( [] , [] , [] ) .
list_sum( [] , [Y|Ys] , [Z|Zs] ) :- Z is 0+Y , list_sum( [] , Ys , Zs ) .
list_sum( [X|Xs] , [] , [Z|Zs] ) :- Z is X+0 , list_sum( Xs , [] , Zs ) .
list_sum( [X|Xs] , [Y|Ys] , [Z|Zs] ) :- Z is X+Y , list_sum( Xs , Ys , Zs ) .

The query to execute this is: list_sum([1,2,3],[3,4,5],L3).

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