1
+ => number
successor
1
- => number
predecessor
number--a number.
successor, predecessor--a number.
1+ returns a number that is one more than its argument number. 1- returns a number that is one less than its argument number.
(1+ 99) => 100 (1- 100) => 99 (1+ (complex 0.0)) => #C(1.0 0.0) (1- 5/3) => 2/3
Might signal type-error if its argument is not a number. Might signal arithmetic-error.
(1+ number) == (+ number 1) (1- number) == (- number 1)
Implementors are encouraged to make the performance of both the previous expressions be the same.