negative?, positive?, odd?, even?, flnegative?, flpositive?, flodd?, fleven?, fxnegative?, fxpositive?, fxodd?, fxeven? - numerical predicates

(import (rnrs))                     ;R6RS
(import (rnrs base))                ;R6RS
(import (scheme r5rs))              ;R7RS
(import (scheme base))              ;R7RS
(import (rnrs arithmetic flonums))  ;R6RS
(import (rnrs arithmetic fixnums))  ;R6RS

(negative? x)
(positive? x)
(odd? n)
(even? n)
;; R6RS
(flnegative? fl)
(flpositive? fl)
(flodd? fl)
(fleven? fl)
(fxnegative? fx)
(fxpositive? fx)
(fxodd? fx)
(fxeven? fx)

These numerical predicates test a number object for a particular property, returning #t or #f.

Properties tested

The predicates tests the following properties.

zero?	tests if the number is = to zero
positive?	tests if the number is greater than zero
negative?	tests if the number is less than zero
odd?	tests if the number is odd
even?	tests if the number is even

Flonum variants

These variants restrict their arguments to flonums.

Fixnum variants

These variants restrict their arguments to fixnums.

Unless the number is exact, the results may be unreliable because a small inaccuracy may affect the result.

Returns a single value; a boolean.

(zero? +0.0)        =>  #t
(zero? -0.0)        =>  #t
(zero? +nan.0)      =>  #f
(positive? +inf.0)  =>  #t
(negative? -inf.0)  =>  #t
(positive? +nan.0)  =>  #f
(negative? +nan.0)  =>  #f

These procedures work the same in all Scheme revisions since R2RS.

This procedure can raise exceptions with the following condition types:

&assertion (R6RS)

The wrong number of arguments was passed or an argument was outside its domain.

R7RS

The assertions described above are errors. Implementations may signal an error, extend the procedure's domain of definition to include such arguments, or fail catastrophically.

>(3scm), finite?(3scm)

R4RS, IEEE Scheme, R5RS, R6RS, R7RS

These procedures were first introduced in R2RS. Scheme before then, running on MacLisp, had access to similar predicates: zerop, plusp, minusp, and oddp. LISP 1.5 had a minusp predicate that returned true for negative numbers, including -0. It also had zerop and onep predicates. These were specified to true when the absolute difference between the argument and zero or one, respectively, is less than 3e-6.

This page is part of the scheme-manpages project. It includes materials from the RnRS documents. More information can be found at https://weinholt.se/scheme/manpages/.