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node_modules/date-fns/docs/fp.md

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+# FP Guide
+
+**date-fns** v2.x provides [functional programming](https://en.wikipedia.org/wiki/Functional_programming) (FP)
+friendly functions, like those in [lodash](https://github.com/lodash/lodash/wiki/FP-Guide),
+that support [currying](https://en.wikipedia.org/wiki/Currying).
+
+## Table of Contents
+
+- [Usage](#usage)
+
+- [Using Function Composition](#using-function-composition)
+
+## Usage
+
+FP functions are provided via `'date-fns/fp'` submodule.
+
+Functions with options (`format`, `parse`, etc.) have two FP counterparts:
+one that has the options object as its first argument and one that hasn't.
+The name of the former has `WithOptions` added to the end of its name.
+
+In **date-fns'** FP functions, the order of arguments is reversed.
+
+```javascript
+import { addYears, formatWithOptions } from "date-fns/fp";
+import { eo } from "date-fns/locale";
+import toUpper from "lodash/fp/toUpper"; // 'date-fns/fp' is compatible with 'lodash/fp'!
+
+// If FP function has not received enough arguments, it returns another function
+const addFiveYears = addYears(5);
+
+// Several arguments can be curried at once
+const dateToString = formatWithOptions({ locale: eo }, "d MMMM yyyy");
+
+const dates = [
+  new Date(2017, 0 /* Jan */, 1),
+  new Date(2017, 1 /* Feb */, 11),
+  new Date(2017, 6 /* Jul */, 2),
+];
+
+const formattedDates = dates.map(addFiveYears).map(dateToString).map(toUpper);
+//=> ['1 JANUARO 2022', '11 FEBRUARO 2022', '2 JULIO 2022']
+```
+
+## Using Function Composition
+
+The main advantage of FP functions is support of functional-style
+[function composing](https://medium.com/making-internets/why-using-chain-is-a-mistake-9bc1f80d51ba).
+
+In the example above, you can compose `addFiveYears`, `dateToString` and `toUpper` into a single function:
+
+```javascript
+const formattedDates = dates.map((date) =>
+  toUpper(dateToString(addFiveYears(date))),
+);
+```
+
+Or you can use `compose` function provided by [lodash](https://lodash.com) to do the same in more idiomatic way:
+
+```javascript
+import { compose } from "lodash/fp/compose";
+
+const formattedDates = dates.map(compose(toUpper, dateToString, addFiveYears));
+```
+
+Or if you prefer natural direction of composing (as opposed to the computationally correct order),
+you can use lodash' `flow` instead:
+
+```javascript
+import flow from "lodash/fp/flow";
+
+const formattedDates = dates.map(flow(addFiveYears, dateToString, toUpper));
+```