Add Hashable typeclass

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#188 10 comentarios 4 reacciones 0 asignados Ver en GitHub

Nadie ha tomado este issue todavía.

Evaluación

Dificultad
5/5
Tiempo estimado
Más de una semana
Aptitud para principiantes
20/100
Tipo de issue
Nueva funcionalidad
Claridad
Bastante claro
Estado de actividad
Estancado
Área
backend

Línea de trabajo

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.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

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?

Lenguaje dominante
PureScript
Estrellas
168
Forks
90
Merge medio
3 d 1 h
PR fusionados (30 d)
1

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  • Tiene una plantilla de pull request
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Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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