eslint-plugin-functype

Custom ESLint rules for functional TypeScript with functype. Encourages idiomatic functype patterns like Option, Either, List, Do notation, and safe data access.

Install

npm install -D eslint-plugin-functype eslint

Usage

// eslint.config.mjs
import functype from "eslint-plugin-functype"

export default [functype.configs.recommended]

Strict mode

import functype from "eslint-plugin-functype"

export default [functype.configs.strict]

Rules

| Rule | Recommended | Strict | Description | | ------------------------------ | :---------: | :----: | -------------------------------------------------------- | | functype/prefer-option | warn | error | Use Option/Some/None instead of null/undefined | | functype/prefer-either | warn | error | Use Either/Right/Left instead of throwing | | functype/prefer-fold | warn | warn | Use fold/match instead of manual unwrapping | | functype/prefer-map | warn | warn | Use map instead of manual option/either checks | | functype/prefer-flatmap | warn | warn | Use flatMap instead of nested map | | functype/no-imperative-loops | warn | warn | Use List methods instead of imperative loops | | functype/prefer-do-notation | warn | warn | Use Do notation for chained operations | | functype/no-get-unsafe | off | error | Disallow unsafe .get() on Option/Either | | functype/prefer-list | off | warn | Use List instead of native arrays |

Combining with eslint-config-functype

For a complete setup with functional rules, TypeScript, Prettier, and import sorting:

npm install -D eslint-config-functype eslint-plugin-functype

import recommended from "eslint-config-functype/recommended"
import testOverrides from "eslint-config-functype/test-overrides"
import functype from "eslint-plugin-functype"

export default [recommended, functype.configs.recommended, testOverrides]

License

MIT