Add Hashable typeclass

Aperta
  • Qualcosa non va?
#188 10 commenti 4 reazioni 0 assegnatari Vedi su GitHub

Nessuno ha ancora preso questa issue.

Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
20/100
Tipo di issue
Funzionalità
Chiarezza
Abbastanza chiara
Stato di attività
Ferma
Ambito
backend

Direzione di ricerca

The issue proposes adding a Hashable typeclass to the prelude and deriving support to the compiler, but names no files or tests. Start by reviewing the existing Eq and Ord typeclasses and the linked purescript-unordered-collections implementation. Done means agreeing on the design and adding the prelude typeclass and compiler deriving support; the thread has had no comment for years, so check whether the proposal is still wanted.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

status: blocked

I would like to add a Hashable typeclass to the prelude and deriving support for it to the compiler. It is intended as an approximation of equality for use in hash-based algorithms and data structures, such as hash maps, not cryptographically secure digests or password hashes.

class Eq a <= Hashable a where
  hash :: a -> Int

There are two reasons for adding it to the prelude instead of having a standalone library:

  1. Dependencies: To be useful in general data structures, as many datatypes as possible should be hashable. Ideally, whenever a datatype is Eq, it should also have Ord and Hashable instances, if possible. Most packages depend on the prelude already.[citation needed] This should make it easier to convince authors to add Hashable instances, because they do not need to add another dependency, all that is required is one more deriving line below the lines for Eq and Ord.
  2. Performance: Usually, the main goal of hashing is to avoid expensive comparisons. One could write a generic hash function in terms of purescript-generics-rep. This would be fine for many applications, but for hash-based data structures etc., the hash function should really be as fast as possible.

I am more than happy to make an initial pull request (based on https://github.com/fehrenbach/purescript-unordered-collections/blob/master/src/Data/Hashable.purs) and work on deriving support.

What do people think?

Lingua principale
PureScript
Stelle
168
Fork
90
Merge medio
3g 1h
PR unite (30g)
1

Preparare l'ambiente

  • Nessun Dockerfile né file Docker Compose
  • Ha un modello di pull request
  • Nessuna guida per i contributori

Come iniziare

  1. Leggi tutta la issue e poi la guida ai contributi del progetto.
  2. Commenta sulla issue per dire che te ne occupi tu — evita che due persone facciano lo stesso lavoro.
  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

Altre issue di purescript/purescript-prelude

Tutte le issue di purescript/purescript-prelude

Issue simili

Altre issue su Backend & API Design

Ricevi le nuove issue nella tua casella

Un breve riepilogo di issue GitHub adatte ai principianti.