{"id":19711014,"url":"https://github.com/eilvelia/contravariant","last_synced_at":"2026-03-04T22:01:19.874Z","repository":{"id":57206670,"uuid":"157470156","full_name":"eilvelia/contravariant","owner":"eilvelia","description":"Contravariant functors in JavaScript + Flow with correct type 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unexpected eof while reading","robots_txt_status":"success","robots_txt_updated_at":"2025-07-24T06:49:26.215Z","robots_txt_url":"https://github.com/robots.txt","online":false,"can_crawl_api":true,"host_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub","repositories_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories","repository_names_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repository_names","owners_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners"}},"keywords":["fantasy-land","functional-programming"],"created_at":"2024-11-11T22:09:18.729Z","updated_at":"2026-03-04T22:01:19.819Z","avatar_url":"https://github.com/eilvelia.png","language":"JavaScript","funding_links":[],"categories":[],"sub_categories":[],"readme":"# contravariant\n\n[![npm](https://img.shields.io/npm/v/contravariant.svg)](https://www.npmjs.com/package/contravariant)\n[![Build Status](https://travis-ci.org/Bannerets/contravariant.svg?branch=master)](https://travis-ci.org/Bannerets/contravariant)\n\nContravariant functors in JavaScript with [Flow](https://flow.org/).\n\nMainly inspired by haskell [contravariant](https://hackage.haskell.org/package/contravariant).\n\nSee [src/index.js](src/index.js) and [test/index.test.js](test/index.test.js).\n\n## Installation\n\n```console\n$ npm install contravariant\n```\n\n## API\n\n`interface IContravariant\u003c-A\u003e`\n\n- `contramap\u003cB\u003e(fn: B =\u003e A): IContravariant\u003cB\u003e`\n\n---\n\n`class Predicate\u003c-A\u003e`\n\n- `constructor(f: A =\u003e boolean)`\n- `getPredicate(): A =\u003e boolean`\n- `contramap\u003cB\u003e(fn: B =\u003e A): Predicate\u003cB\u003e`\n\n---\n\n`class Comparison\u003c-A\u003e`\n\n- `constructor(f: (A, A) =\u003e number)`\n- `getComparison(): (A, A) =\u003e number`\n- `contramap\u003cB\u003e(fn: B =\u003e A): Comparison\u003cB\u003e`\n\n`function defaultComparison(): Comparison\u003cnumber\u003e`\n\n---\n\n`class Equivalence\u003c-A\u003e`\n\n- `constructor(f: (A, A) =\u003e boolean)`\n- `getEquivalence(): (A, A) =\u003e boolean`\n- `contramap\u003cB\u003e(fn: B =\u003e A): Equivalence\u003cB\u003e`\n\n`function defaultEquivalence\u003cA\u003e(): Equivalence\u003cA\u003e`\n\n---\n\n`class Op\u003c+A, -B\u003e`\n\n- `constructor(f: B =\u003e A)`\n- `getOp(): B =\u003e A`\n- `contramap\u003cBB\u003e(fn: BB =\u003e B): Op\u003cA, BB\u003e`\n\n---\n\n### Profunctors\n\n`interface IProfunctor\u003c-B, +C\u003e`\n\n- `promap\u003cA, D\u003e(fn1: A =\u003e B, fn2: C =\u003e D): IProfunctor\u003cA, D\u003e`\n\n---\n\n`class Arrow\u003c-B, +C\u003e`\n\n- `constructor(f: B =\u003e C)`\n- `getArrow(): B =\u003e C`\n- `promap\u003cA, D\u003e(fn1: A =\u003e B, fn2: C =\u003e D): Arrow\u003cA, D\u003e`\n- `lmap\u003cA\u003e(fn1: A =\u003e B): Arrow\u003cA, C\u003e`\n- `rmap\u003cD\u003e(fn2: C =\u003e D): Arrow\u003cB, D\u003e`\n\n## See also\n\n- https://hackage.haskell.org/package/contravariant-1.5/docs/Data-Functor-Contravariant.html\n- https://gist.github.com/Bannerets/07a71802e3468d252924091a65ac2b3c\n- https://www.schoolofhaskell.com/school/to-infinity-and-beyond/pick-of-the-week/profunctors\n- https://www.fpcomplete.com/blog/2016/11/covariance-contravariance\n- https://hackage.haskell.org/package/profunctors-5.3/docs/Data-Profunctor.html\n- https://github.com/fantasyland/fantasy-land#contravariant\n- https://github.com/fantasyland/fantasy-land#profunctor\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Feilvelia%2Fcontravariant","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Feilvelia%2Fcontravariant","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Feilvelia%2Fcontravariant/lists"}