record-predicate(3scm)

📦 version 0-unstable-2024-02, in nixpkgs unstable

🎀 record-predicate(3scm) 🎀

okay bestie, welcome to the Scheme Programmer's Manual page for record-predicate — this one is lowkey tiny but highkey useful, and it's giving "record type vibe check." 💅

🌸 NAME 🌸

record-predicate — create record predicates. No cap, that's the whole name section. 🫶

🌈 LIBRARY 🌈

okay so you import one of these depending on your setup, and yes, both are R6RS:

(import (rnrs))                     ;R6RS
(import (rnrs records procedural))  ;R6RS

✨ SYNOPSIS ✨

(record-predicate rtd)

💖 DESCRIPTION 💖

So record-predicate returns a procedure. Give that procedure an object obj, and it returns #t if obj is a record of the type represented by rtd, and #f otherwise. That's it — a little yes/no machine for records, and honestly? iconic. 🔥

🦋 RETURN VALUES 🦋

Returns a single value; a procedure. That's the whole return value, bestie — one procedure, no extra baggage. 💅

🍓 EXAMPLES 🍓

here's the exact example, bestie — copy it, run it, live your truth:

(define rtd-user
  (make-record-type-descriptor
    'user #f #f #f #f
    '#((immutable login) (immutable realname))))
(define rcd-user
  (make-record-constructor-descriptor
    rtd-user #f
    (lambda (p)
      (lambda (login realname)
        (p login realname)))))
(define make-user (record-constructor rcd-user))
(define user? (record-predicate rtd-user))

(define lain (make-user 'lain "Lain Iwakura"))
(user? lain)  =>  #t

🧚 APPLICATION USAGE 🧚

These procedures are used together with the procedural record layer. That's the application usage, and it's giving "we ride together, we record together." 🫶

💜 COMPATIBILITY 💜

This procedure is unique to the R6RS record system. An equivalent procedure can be found in SRFI-237. So if you're in R6RS land, you're chilling; if not, SRFI-237 has your back. ✨

⭐ 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. In particular, rtd must be a record-type descriptor. So yeah, don't hand it random nonsense and expect peace, okay? 😭

👑 SEE ALSO 👑

go read these too, bestie:

🌟 STANDARDS 🌟

R6RS. periodt. 💅

🎀 HISTORY 🎀

First appeared in R6RS as part of the new record system. A little origin story, a little lore. 🦋

🌸 AUTHORS 🌸

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

💌 That's a wrap, bestie — source/version: Scheme Programmer's Manual, date: 2023-08-05, page: record-predicate(3scm). Mwah! 🫶

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