Add Hashable typeclass

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#188 10 comentários 4 reações 0 responsáveis Ver no GitHub

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Avaliação

Dificuldade
5/5
Tempo estimado
Mais de uma semana
Facilidade para iniciantes
20/100
Tipo de issue
Funcionalidade
Clareza
Razoavelmente clara
Status de atividade
Estagnada
Domínio
backend

Direção de pesquisa

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.

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Descrição

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?

Linguagem predominante
PureScript
Estrelas
168
Forks
90
Merge médio
3d 1h
PRs com merge (30d)
1

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