or(7scm)

💖 or — the short-circuiting vibe check 💖

okay so this is or(7scm), straight out of the Scheme Programmer's Manual, and bestie it is literally the "first true thing wins" icon we all need. no cap.

✨ LIBRARY ✨

where you gotta import it from, depending on your whole era:

(import (rnrs))                     ;R6RS
(import (rnrs base))                ;R6RS
(import (scheme r5rs))              ;R7RS
(import (scheme base))              ;R7RS

🎀 SYNOPSIS 🎀

(or test ...)

that's it. that's the whole flex. 💅

🦋 DESCRIPTION 🦋

so the test expressions get evaluated left to right — like, in order, bestie, one at a time — until one of them hands back a true value, or until you hit the very last test.

if one of them goes true? the whole or expression returns that value and dips out immediately — the remaining expressions do not get evaluated. gone. not today. 🫶

if none of them go true? then the last expression gets evaluated and its values are what you get back.

and if there are, like, zero tests in there? you get #f. 🫠

💀 IMPLEMENTATION NOTES 💀

some implementations are out here with opinions, and honestly? valid.

• Chez Scheme, Loko Scheme — the source-level optimizer can rewrite code that uses multiple values in one of the test expressions in such a way that the values are no longer in a single-value context. which can mean code that would otherwise raise an exception will run without error, but with possibly unexpected results. this is not a bug, bestie, it's permitted by R6RS. the optimizer is just main character energy. 🙈
• Vicare Scheme — the test expressions are statically checked to see that they return a single value. it's giving strict parent. ⭐

🌸 RETURN VALUES 🌸

returns the value of the first true expression. and remember the golden rule: in Scheme everything is true except for the false value (#f or #false in R7RS). literally everything. a number? true. a list? true. your ex? still true. 😭

also — the last test expression is in tail context if the or expression itself is. 🧚

🌈 EXAMPLES 🌈

look at her go:

(or (= 2 2) (> 2 1))  => #t
(or (= 2 2) (< 2 1))  => #t
(or #f #f #f)         => #f
(or '(b c) (/ 3 0))   => (b c)
(or)                  => #f

that fourth one?? '(b c) is true so the (/ 3 0) never runs. no divide-by-zero meltdown. we love a protective queen. 👑

💅 APPLICATION USAGE 💅

the or syntax is very common in almost all programming languages — lowkey everywhere. sometimes it's called or, other times it's && or something else entirely. it's the move when several expressions should be tested but evaluation should not continue past the first true value.

and hey — when your expressions get more complicated, it's better to use cond(3scm). know when to upgrade, bestie. 💜

⭐ COMPATIBILITY ⭐

the or syntax is widely compatible across Lisp systems. fr fr, it's everywhere.

🔥 ERRORS 🔥

this procedure can raise exceptions with the following condition types:

• &assertion (R6RS) — zero or more than one value was returned by a non-tail test expression. implementations may also handle this in another way, as long as the safety guarantees of R6RS § 5.6 are upheld. iykyk.
• 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. that's the word they used. be careful.

🍓 SEE ALSO 🍓

• and(3scm)
• cond(3scm)
• if(3scm)

the whole conditional friend group. go say hi. 🫶

👑 STANDARDS 👑

R4RS, IEEE Scheme, R5RS, R6RS, R7RS — she's certified across the board. iconic behavior.

🧚 HISTORY 🧚

short-circuiting evaluation was invented in the 1950s by John McCarthy, the creator of Lisp. yes, the 1950s. the original trendsetter. periodt. ✨

💖 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, bestie 🌸 — this little love letter was dated 2020-05-03 and it's or(7scm) all the way down. now go short-circuit something responsibly 💅✨