hashtabl...function(3scm)

💅 hashtabl...function(3scm) — like, the hashtable inspection girlies ✨

okay so before we even start: welcome to the Scheme Programmer's Manual, bestie 🎀 this particular page is the hashtable inspection trio and honestly? they're the backstage-pass besties of the hashtable world. let's go 🌸

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✨ NAME ✨

hashtable-equivalence-function, hashtable-hash-function, hashtable-mutable? — the hashtable inspection functions, aka the "wait, what's in this thing" girlies 🔍

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📚 LIBRARY 📚

(import (rnrs))                     ;R6RS
(import (rnrs hashtables))          ;R6RS

two ways in, both R6RS, pick your fighter 💖

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🦋 SYNOPSIS 🦋

(hashtable-equivalence-function hashtable)
(hashtable-hash-function hashtable)
(hashtable-mutable? hashtable)

three procedures, one hashtable argument each. iconic, minimal, no notes 🫶

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💫 DESCRIPTION 💫

hashtable-equivalence-function

this one hands you back the equivalence function that hashtable uses to compare keys 👑 and here's the slay: if the hashtable was created by make-eq-hashtable(3scm) or make-eqv-hashtable(3scm), you get the procedure objects eq? and eqv? respectively. literally just hands you the actual function object. no cap 💅

hashtable-hash-function

returns the hash function that hashtable is using. but plot twist 😭 — if the hashtable came from make-eq-hashtable(3scm) or make-eqv-hashtable(3scm), this one returns #f. yeah. #f. that's the whole vibe for those two.

hashtable-mutable?

the vibe check of the group 🌈 returns #t if hashtable is mutable, otherwise #f. that's it. that's the procedure.

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🎁 RETURN VALUES 🎁

all three return a single value — an object as described above. one value, no bundling, we're not doing that here 🎀

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🌸 APPLICATION USAGE 🌸

ngl these procedures are rarely used outside of procedures that print hashtables. that's their whole social circle 🫶 like yes they're serving but they're serving a niche.

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🧚 RATIONALE 🧚

okay so why does hashtable-hash-function be giving #f for the eq/eqv girlies? 👀 because the hash functions for hashtables created by make-eq-hashtable(3scm) or make-eqv-hashtable(3scm) are private to the implementation. and the reason is actually so valid: implementations may use garbage collectors that move objects, and that movement can change the hash value of the affected objects 😭 so yeah, keeping it private is the move. periodt.

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🔥 COMPATIBILITY 🔥

these procedures are unique to R6RS 💜 compatible procedures can sorta be found in SRFI-69, SRFI-125 and SRFI-126. "sorta" is doing a lot of heavy lifting there but we respect it 🫡

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💀 ERRORS 💀

this procedure can raise exceptions with the following condition types:

• &assertion (R6RS) — bestie, the wrong number of arguments was passed, or an argument was outside its domain 😭 in particular, hashtable should be a hashtable. like. that's the bare minimum. please pass a hashtable 🙈

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👀 SEE ALSO 👀

• make-hashtable(3scm) — go read that one next, fr fr

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⭐ STANDARDS ⭐

R6RS 🎀

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🌈 HISTORY 🌈

these procedures first appeared in R6RS's hashtable library, which was based on SRFI-69 — and SRFI-69 also has the first two procedures 💖 so like, they've been around. legacy icons.

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👑 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/ 🦋

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and that's the whole page bestie, tysm for reading 💅✨ mwah 🫶

this lil cutie dropped 2023-01-22 and it lives in the Scheme Programmer's Manual (that's the source/version vibes) — see u in the next manpage, love u, bye 🎀💖