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Merge pull request #55 from buildo/pure-statement
Add no-discarded-pure-expression
2 parents 13a9992 + 597b90f commit 551360f

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‎README.md

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@@ -38,22 +38,48 @@ and enable the rules you want, for example
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}
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```
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If you want to enable rules that require type information (see the table below),
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then you will also need to add some extra info:
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```js
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module.exports = {
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plugins: ["fp-ts"],
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parserOptions: {
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tsconfigRootDir: __dirname,
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project: ["./tsconfig.json"],
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},
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rules: {
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"fp-ts/no-discarded-pure-expression": "error",
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},
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};
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```
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If your project is a multi-package monorepo, you can follow the instructions
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[here](https://github.com/typescript-eslint/typescript-eslint/blob/master/docs/getting-started/linting/MONOREPO.md).
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> ⚠️ Note that you will need to make the ESLint config file a .js file, due to
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> the need of setting `tsconfigRootDir` to `__dirname`. This is necessary to
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> make both editor integrations and the CLI work with the correct path. More
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> info here: https://github.com/typescript-eslint/typescript-eslint/issues/251
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## List of supported rules
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- [fp-ts/no-lib-imports](docs/rules/no-lib-imports.md): Disallow imports from
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'fp-ts/lib' (autofixable 🔧)
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- [fp-ts/no-pipeable](docs/rules/no-pipeable.md): Disallow imports from the
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'pipeable' module (autofixable 🔧)
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- [fp-ts/no-module-imports](docs/rules/no-module-imports.md): Disallow imports
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from fp-ts modules (autofixable 🔧)
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- [fp-ts/no-redundant-flow](docs/rules/no-redundant-flow.md): Remove redundant
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uses of flow (autofixable 🔧)
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- [fp-ts/prefer-traverse](docs/rules/prefer-traverse.md): Replace map + sequence
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with traverse (autofixable 🔧)
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- [fp-ts/prefer-chain](docs/rules/prefer-chain.md): Replace map + flatten with
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chain (autofixable 🔧)
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- [fp-ts/prefer-bimap](docs/rules/prefer-bimap.md): Replace map + mapLeft with
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bimap (autofixable 🔧)
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| Rule | Description | Fixable | Requires type-checking |
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| -------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------ | :-----: | :--------------------: |
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| [fp-ts/no-lib-imports](docs/rules/no-lib-imports.md) | Disallow imports from `fp-ts/lib/` | 🔧 | |
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| [fp-ts/no-pipeable](docs/rules/no-pipeable.md) | Disallow imports from the `pipeable` module | 🔧 | |
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| [fp-ts/no-module-imports](docs/rules/no-module-imports.md) | Disallow imports from fp-ts modules | 🔧 | |
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| [fp-ts/no-redundant-flow](docs/rules/no-redundant-flow.md) | Remove redundant uses of `flow` | 🔧 | |
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| [fp-ts/prefer-traverse](docs/rules/prefer-traverse.md) | Replace `map` + `sequence` with `traverse` | 💡 | |
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| [fp-ts/prefer-chain](docs/rules/prefer-chain.md) | Replace `map` + `flatten` with `chain` | 💡 | |
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| [fp-ts/prefer-bimap](docs/rules/prefer-bimap.md) | Replace `map` + `mapLeft` with `bimap` | 💡 | |
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| [fp-ts/no-discarded-pure-expression](docs/rules/no-discarded-pure-expression.md) | Disallow expressions returning pure data types (like `Task` or `IO`) in statement position | 💡 | 🦄 |
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### Fixable legend:
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🔧 = auto-fixable via `--fix` (or via the appropriate editor configuration)
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💡 = provides in-editor suggestions that need to be applied manually
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## Configurations
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- [fp-ts/no-lib-imports](docs/rules/no-lib-imports.md)
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- [fp-ts/no-pipeable](docs/rules/no-pipeable.md)
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### Recommended requiring type-checking
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We also provide a `recommended-requiring-type-checking` which includes
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recommended rules which require type information.
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This configuration needs to be included _in addition_ to the `recommended` one:
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```
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{
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"extends": [
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"plugin:fp-ts/recommended"
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"plugin:fp-ts/recommended-requiring-type-checking"
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]
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}
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```
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> 👉 You can read more about linting with type information, including
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> performance condideration
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> [here](https://github.com/typescript-eslint/typescript-eslint/blob/master/docs/getting-started/linting/TYPED_LINTING.md)
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### All
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The plugin also defines an `all` configuration which includes every available

‎docs/rules/no-discarded-pure-expression.md

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# Disallow expressions returning pure data types (like `Task` or `IO`) where `void` or `unknown` is expected or in statement position (fp-ts/no-discarded-pure-expression)
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Expressions which return a pure data type, such as `IO`, `Task` and their
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variants, should normally be passed as an argument, returned, or run.
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Failing to do so causes the program represented by `IO` or `Task` to never be
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run, leading to surprising behavior which is normally difficult to debug.
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This rule covers two common scenarios that are common programming errors:
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- returning pure data types where `void` or `unknown` is expected (for instance,
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in event handlers) without running them
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- writing expressions that return pure data types in statement position (without
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returning them or running them)
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**💡 Fixable**: This rule provides in-editor suggested fixes.
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## Rule Details
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Examples of **incorrect** code for this rule:
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```ts
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import { task } from "fp-ts";
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declare const myCommand: (n: number) => Task<string>;
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function woops() {
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myCommand(1); // the task will never run, since is not being run nor returned
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}
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```
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```ts
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declare const MyComponent: (props: { handler: () => void }) => JSX.Element;
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declare const myCommand: (n: number) => Task<string>;
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export function Foo() {
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return (
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<MyComponent
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handler={() => myCommand(1)} // bug, the Task will never execute
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/>;
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)
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}
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```
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```ts
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import { task } from "fp-ts";
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declare function foo(arg1: number, callbackUnknown: () => unknown): void;
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declare const myCommand: (n: number) => Task<string>;
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foo(
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2,
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() => myCommand(1) // bug, the Task will never execute
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);
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```
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Examples of **correct** code for this rule:
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```ts
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import { task } from "fp-ts";
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declare const myCommand: (n: number) => Task<string>;
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function ok() {
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return myCommand(1);
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}
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```
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```ts
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declare const MyComponent: (props: { handler: () => void }) => JSX.Element;
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declare const myCommand: (n: number) => Task<string>;
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export function Foo() {
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return (
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<MyComponent
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handler={() => myCommand(1)()}
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/>;
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)
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}
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```
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```ts
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import { task } from "fp-ts";
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declare function foo(arg1: number, callbackUnknown: () => unknown): void;
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declare const myCommand: (n: number) => Task<string>;
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foo(2, () => myCommand(1)());
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```

‎docs/rules/no-lib-imports.md

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> Note: this change was introduced in fp-ts 2.8.0. If you are using an older
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> version, do not enable this rule
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**Fixable**: This rule is automatically fixable using the `--fix` flag on the
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**🔧 Fixable**: This rule is automatically fixable using the `--fix` flag on the
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command line.
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## Rule Details

‎docs/rules/no-module-imports.md

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The `function` module is an exception and it's allowed nonetheless, since it's
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not exported from fp-ts's index.
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**Fixable**: This rule is automatically fixable using the `--fix` flag on the
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**🔧 Fixable**: This rule is automatically fixable using the `--fix` flag on the
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command line.
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## Rule Details

‎docs/rules/no-pipeable.md

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it will be removed in future versions of fp-ts. It's recommended to import
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`pipe` from the `function` module instead.
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**Fixable**: This rule is automatically fixable using the `--fix` flag on the
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**🔧 Fixable**: This rule is automatically fixable using the `--fix` flag on the
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command line.
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> Note: the autofix is available only when importing `pipe`

‎docs/rules/no-redundant-flow.md

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Suggest removing `flow` when it only has one argument. This can happen after a
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refactoring that removed some combinators from a flow expression.
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**Fixable**: This rule is automatically fixable using the `--fix` flag on the
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command line.
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**💡 Fixable**: This rule provides in-editor suggested fixes.
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## Rule Details
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‎docs/rules/prefer-bimap.md

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Suggest replacing the combination of `map` followed by `mapLeft` (or vice-versa)
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with `bimap`.
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**Fixable**: This rule is automatically fixable using the `--fix` flag on the
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command line.
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**💡 Fixable**: This rule provides in-editor suggested fixes.
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## Rule Details
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‎docs/rules/prefer-chain.md

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Suggest replacing the combination of `map` (or `mapWithIndex`) followed by
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`flatten` with `chain` (or `chainWithIndex`).
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**Fixable**: This rule is automatically fixable using the `--fix` flag on the
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command line.
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**💡 Fixable**: This rule provides in-editor suggested fixes.
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## Rule Details
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‎docs/rules/prefer-traverse.md

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Suggest replacing the combination of `map` (or `mapWithIndex`) followed by
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`sequence` with `traverse` (or `traverseWithIndex`).
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**Fixable**: This rule is automatically fixable using the `--fix` flag on the
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command line.
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**💡 Fixable**: This rule provides in-editor suggested fixes.
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## Rule Details
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‎package.json

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"scripts": {
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"preversion": "yarn lint && yarn test && yarn build",
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"build": "rimraf lib && yarn tsc",
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"pretest": "yarn --cwd tests/fixtures/fp-ts-project install",
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"test": "jest",
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"lint": "eslint src/**/*.ts"
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},

‎src/index.ts

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"no-lib-imports": require("./rules/no-lib-imports").default,
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"no-pipeable": require("./rules/no-pipeable").default,
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"no-module-imports": require("./rules/no-module-imports").default,
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"no-discarded-pure-expression": require("./rules/no-discarded-pure-expression")
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.default,
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};
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const suggestions = {
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"fp-ts/no-pipeable": "error",
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},
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},
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"recommended-requiring-type-checking": {
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plugins: ["fp-ts"],
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rules: {
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"fp-ts/no-discarded-pure-expression": "error",
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},
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},
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all: {
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plugins: ["fp-ts"],
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rules: {

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