{"id":23902891,"url":"https://github.com/mtumilowicz/java11-category-theory-reader-functor","last_synced_at":"2025-08-13T19:07:14.162Z","repository":{"id":110876631,"uuid":"163865231","full_name":"mtumilowicz/java11-category-theory-reader-functor","owner":"mtumilowicz","description":"Simple implementation of Reader Functor.","archived":false,"fork":false,"pushed_at":"2019-01-16T16:59:09.000Z","size":66,"stargazers_count":4,"open_issues_count":0,"forks_count":1,"subscribers_count":1,"default_branch":"master","last_synced_at":"2025-04-15T14:14:07.178Z","etag":null,"topics":["category-theory","functors","reader","reader-functor"],"latest_commit_sha":null,"homepage":"","language":"Java","has_issues":true,"has_wiki":null,"has_pages":null,"mirror_url":null,"source_name":null,"license":null,"status":null,"scm":"git","pull_requests_enabled":true,"icon_url":"https://github.com/mtumilowicz.png","metadata":{"files":{"readme":"README.md","changelog":null,"contributing":null,"funding":null,"license":null,"code_of_conduct":null,"threat_model":null,"audit":null,"citation":null,"codeowners":null,"security":null,"support":null,"governance":null,"roadmap":null,"authors":null,"dei":null,"publiccode":null,"codemeta":null,"zenodo":null}},"created_at":"2019-01-02T16:36:19.000Z","updated_at":"2024-11-25T09:22:19.000Z","dependencies_parsed_at":"2023-03-13T13:47:40.119Z","dependency_job_id":null,"html_url":"https://github.com/mtumilowicz/java11-category-theory-reader-functor","commit_stats":null,"previous_names":[],"tags_count":0,"template":false,"template_full_name":null,"purl":"pkg:github/mtumilowicz/java11-category-theory-reader-functor","repository_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/mtumilowicz%2Fjava11-category-theory-reader-functor","tags_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/mtumilowicz%2Fjava11-category-theory-reader-functor/tags","releases_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/mtumilowicz%2Fjava11-category-theory-reader-functor/releases","manifests_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/mtumilowicz%2Fjava11-category-theory-reader-functor/manifests","owner_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/owners/mtumilowicz","download_url":"https://codeload.github.com/mtumilowicz/java11-category-theory-reader-functor/tar.gz/refs/heads/master","sbom_url":"https://repos.ecosyste.ms/api/v1/hosts/GitHub/repositories/mtumilowicz%2Fjava11-category-theory-reader-functor/sbom","host":{"name":"GitHub","url":"https://github.com","kind":"github","repositories_count":270295851,"owners_count":24560351,"icon_url":"https://github.com/github.png","version":null,"created_at":"2022-05-30T11:31:42.601Z","updated_at":"2022-07-04T15:15:14.044Z","status":"online","status_checked_at":"2025-08-13T02:00:09.904Z","response_time":66,"last_error":null,"robots_txt_status":"success","robots_txt_updated_at":"2025-07-24T06:49:26.215Z","robots_txt_url":"https://github.com/robots.txt","online":true,"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":["category-theory","functors","reader","reader-functor"],"created_at":"2025-01-04T22:51:00.037Z","updated_at":"2025-08-13T19:07:14.131Z","avatar_url":"https://github.com/mtumilowicz.png","language":"Java","funding_links":[],"categories":[],"sub_categories":[],"readme":"[![Build Status](https://travis-ci.com/mtumilowicz/java11-category-theory-reader-functor.svg?branch=master)](https://travis-ci.com/mtumilowicz/java11-category-theory-reader-functor)\n\n# java11-category-theory-reader-functor\n_Reference_: https://bartoszmilewski.com/2015/01/20/functors/\n\n# preface\nBasic knowledge and intuition about functors is provided in: \nhttps://github.com/mtumilowicz/java11-category-theory-optional-is-not-functor\n\n**Reader functor**:\n```\nType constructor: (-\u003e a) // curried (-\u003e a b) or equivallent (a -\u003e b)\n\nmap :: (a -\u003e b) -\u003e (r -\u003e a) -\u003e (r -\u003e b)\nmap f g = (.) f g\n```\n\n# proof\n1. `map id = id`\n    ```\n    map id g\n    = { definition of map }\n    (.) id g\n    ```\n1. `map (g . f) = map g . map f`\n    ```\n    map (g . f) h \n    = { definition of map }\n    (.) (g . f) h\n    = { associativity of composition }\n    (.) g (f . h)\n    = { definition of map }\n    map g (f h)\n    = { definition of map }\n    map g (map f h)\n    = { definition of composition }\n    (map g . map f) h\n    ```\n    \n# project description\n* We provide simple implementation of Reader Functor:\n    ```\n    @FunctionalInterface\n    interface Reader\u003cR, A\u003e extends Function\u003cR, A\u003e {\n        default \u003cB\u003e Reader\u003cR, B\u003e map(Function\u003cA, B\u003e f) {\n            return asReader(f.compose(this));\n        }\n        \n        default \u003cX, Y\u003e Reader\u003cX, Y\u003e asReader(Function\u003cX, Y\u003e f) {\n            return f::apply;\n        }\n    }\n    ``` \n* and basic test\n    ```\n    Reader\u003cBigDecimal, Integer\u003e toInteger = BigDecimal::intValue;\n    Reader\u003cBigDecimal, String\u003e mapped = toInteger.map(String::valueOf);\n    \n    assertThat(mapped.apply(BigDecimal.TEN), is(\"10\"));\n    ```\n# additional info\n1. Reader could be extended to monad: \nhttps://github.com/aol/cyclops/blob/master/cyclops-pure/src/main/java/cyclops/control/Reader.java\n1. and used for dependency injection: \nhttps://github.com/aol/cyclops/wiki/Reader-:-functional-dependency-injection","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fmtumilowicz%2Fjava11-category-theory-reader-functor","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fmtumilowicz%2Fjava11-category-theory-reader-functor","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fmtumilowicz%2Fjava11-category-theory-reader-functor/lists"}