typelevel/cats

Add Divisible and Decideable (contravariant Applicative and co.)

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#1,935 opened on Sep 27, 2017

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 (22 comments) (5 reactions) (0 assignees)Scala (5,438 stars) (1,241 forks)batch import
help wanted

Description

https://hackage.haskell.org/package/contravariant-1.4/docs/Data-Functor-Contravariant-Divisible.html

Example use case: divide can be seen as a way of deriving behavior by splitting a "larger" type in two

Contributor guide

Tech stack
scala
Domain
backend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
cats library basicstype classescontravariant functorsscala syntax
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Research the Divisible and Decidable type classes from the Haskell contravariant package (https://hackage.haskell.org/package/contravariant 1.4/docs/Data Functor Contravariant Divisible.html). Study the existing Contravariant type class in cats (e.g., cats core/src/main/scala/cats/Contravariant.scala) to understand the pattern. Define new Divisible and Decidable traits and provide instances for common types. Since the issue has been open long, consider posting a design proposal before implementation to ensure maintainer alignment.