typelevel / typelevel/cats

How should we deal with typeclasses that need particular instances of other typeclasses to be lawful?

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Dominant language
Scala
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Description

See: https://github.com/non/algebra/pull/126#discussion_r45569352

Group[Map[K, V]] needs a vetor space style Eq[Map[K, V]] that considers eqv(Some(0), None)

one proposal is for the dependant typeclass to have as a member the depended typeclass (def eqInst: Eq[Map[K, V]])

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked algebra pull request discussion and the proposal for a dependent typeclass to expose its required instance. No source file or test is named in the issue, so trace the relevant typeclass definitions and instance resolution behavior. Done means agreeing on a lawful, implementable design for dependent instances.

Written by the indexing model from the issue text.

Assessment

Tech stack
scala
Domain
backend-api-design
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
25/100

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