negative?(3scm)

💅 negative?(3scm) ✨

okay so this is a page from the Scheme Programmer's Manual and it's literally all about the numerical predicates — the little vibe-check functions that look at a number and go "yeah" or "nope" 🎀

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🌸 NAME

negative?, positive?, odd?, even?, flnegative?, flpositive?, flodd?, fleven?, fxnegative?, fxpositive?, fxodd?, fxeven? — the numerical predicates, periodt 👑

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📚 LIBRARY

here's where you import these besties from, iykyk:

(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

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✨ SYNOPSIS

(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)

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💖 DESCRIPTION

So these are the numerical predicates — they take a number object, check it for one specific property, and hand you back #t or #f. that's it, that's the whole job 🫶

🔍 Properties tested

the predicates check these properties, no cap:

• 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 are picky — they restrict their arguments to flonums only, respectfully 💅

🎀 Fixnum variants

same energy, different lane: these variants restrict their arguments to fixnums.

⚠️ heads up bestie: unless the number is exact, the results may be unreliable, because a tiny little inaccuracy can straight up flip the answer. so like… be careful with your inexact numbers fr fr 😭

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🌈 RETURN VALUES

returns a single value — a boolean. iconic behavior, honestly.

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⭐ EXAMPLES

(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

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🧚 COMPATIBILITY

these procedures work the same in all Scheme revisions since R2RS. consistent queen behavior since day one 👑

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💀 ERRORS

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. 🙈 yeah, catastrophically. not a drill.

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🔥 SEE ALSO

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

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🏆 STANDARDS

R4RS, IEEE Scheme, R5RS, R6RS, R7RS

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🕰️ HISTORY

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 be true when the absolute difference between the argument and zero or one, respectively, is less than 3e-6. so yeah, history was doing its own thing 💜

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👑 AUTHORS

this page is part of the scheme-manpages project. it includes materials from the RnRS documents. more info lives at https://github.com/schemedoc/manpages/.

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🌸 okay that's the whole page!! sourced from the scheme-manpages project, dated 2022-05-10, and honestly? ate. go forth and predicate, bestie 💖✨