+ function computes sum of numbers. It does type conversions for numbers. There is no wraparound in integer numbers - they are arbitrary long. It works for all number types including integer, rational, floating point and complex.

(+ 1 2 3) => 6
(+ 1 2) => 3
(+ 1) => 1
(+) => 0

(+ 1234567890123456789 9876543210987654321) => 11111111101111111110
(+ 1.3 -5) => -3.7
(+ 1.3d0 -5) => -3.7d0
(+ #c(2 4) 1) => #C(3 4)
(+ 3/4 7/9) => 55/36