1+, 1

1+, 1*− Function*

Syntax:

1+ number → successor

1*− number → predecessor*

Arguments and Values:

number—a number .

successor, predecessor—a number .

Description:

1+ returns a number that is one more than its argument number. 1- returns a number that is one less than its argument number.

Examples:

(1+ 99) → 100 
(1- 100) → 99 
(1+ (complex 0.0)) → #C(1.0 0.0) 
(1- 5/3) → 2/3 

Exceptional Situations:

Might signal type-error if its argument is not a number . Might signal arithmetic-error.

See Also:

incf, decf

Notes:

(1+ number) ≡ (+ number 1)

(1- number) ≡ (- number 1)

Implementors are encouraged to make the performance of both the previous expressions be the same.

Expanded Reference: 1+, 1-

1+ returns the number plus one. 1- returns the number minus one.

(1+ 0)
=> 1
(1+ 99)
=> 100
(1- 100)
=> 99
(1- 1)
=> 0

1+ and 1- preserve the rational type when given a rational argument.

(1+ 1/2)
=> 3/2
(1- 5/3)
=> 2/3
(1+ -1/4)
=> 3/4

When given a float, the result is a float of the same format.

(1+ 0.0)
=> 1.0
(1- 1.0d0)
=> 0.0d0
(1+ -1.5)
=> -0.5

1+ and 1- also work with complex numbers.

(1+ #c(0 1))
=> #C(1 1)
(1- #c(3 4))
=> #C(2 4)
(1+ (complex 0.0))
=> #C(1.0 0.0)

1+ and 1- are equivalent to adding or subtracting 1 with + and -.

(= (1+ 42) (+ 42 1))
=> T
(= (1- 42) (- 42 1))
=> T