SWI-Prolog -- plus/3

Documentation
- Reference manual
  - Built-in Predicates
    - Arithmetic
      - Special purpose integer arithmetic
        
        between/3
        
        succ/2
        
        plus/3
        
        divmod/4
        
        nth_integer_root_and_remainder/4
- Packages

Availability:built-in

plus(?Int1, ?Int2, ?Int3)

True if Int3 = Int1 + Int2. At least two of the three arguments must be instantiated to integers.

Examples

?- plus(1,2,X).
X = 3.
?- plus(1,X,3).
X = 2.
?- plus(X,2,3).
X = 1.

Accumulation using foldl/4-7

?- foldl(plus, [1,2,3], 0, N).
N = 6.

Apply predicate to each element in a list

?- maplist(plus(3), [1, X], [Y, 2]).
X = -1,
Y = 4.

Examples for scanl/N

?- scanl(plus, [1,2,3,4,5], 0, Sums).
Sums = [0, 1, 3, 6, 10, 15].

When considering the lists columns of a table, scanl/5 combines the accumulator with each row to produce the next value in the result list. We illustrate this using plus/4 which adds the accumulator with the values from the row to produce the next accumulator. We use trace/2 to illustrate how the values are combined.

plus(A,B,C,Result) :-
    Result is A+B+C.

?- trace(plus/4, exit).
%         plus/4: [exit]
?- scanl(plus, [1,2,3,4,5], [10,20,30,40,50], 0, Sums).
 T Exit: plus(1, 10, 0, 11)
 T Exit: plus(2, 20, 11, 33)
 T Exit: plus(3, 30, 33, 66)
 T Exit: plus(4, 40, 66, 110)
 T Exit: plus(5, 50, 110, 165)
Sums = [0, 11, 33, 66, 110, 165].