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Merge branch 'master' of https://github.com/rescript-lang/rescript-lang.org into vlk-v12-doc-restructure
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‎misc_docs/syntax/decorator_as.mdx

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@@ -6,7 +6,10 @@ summary: "This is the `@as` decorator."
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category: "decorators"
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---
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The `@as` decorator is commonly used on record types to alias record field names to a different JavaScript attribute name.
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The `@as` decorator has multiple uses in ReScript.
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## Change runtime name of record field
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The `@as` decorator can be used on record types to alias record field names to a different JavaScript attribute name.
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This is useful to map to JavaScript attribute names that cannot be expressed in ReScript (such as keywords).
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</CodeTab>
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## Change the runtime representation of a variant constructor
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Similarily to changing the runtime name of a record field, you can change the runtime representation of a variant constructor using `@as()`. Only with variants, you have many more options for the runtime representation than for record field names:
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<CodeTab labels={["ReScript", "JS Output"]}>
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```res
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@unboxed
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type pet = | @as("dog") Dog | @as(1) Cat | @as(null) SomethingElse
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let dog = Dog
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let cat = Cat
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let somethingElse = SomethingElse
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```
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```js
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let dog = "dog";
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let cat = 1;
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let somethingElse = null;
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```
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</CodeTab>
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Read more about the [`@as` decorator and variants](variant.md#valid-as-payloads).
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### References
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* [Bind Using ReScript Record](/docs/manual/latest/bind-to-js-object#bind-using-rescript-record)
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* [Constrain Arguments Better](/docs/manual/latest/bind-to-js-function#constrain-arguments-better)
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* [Fixed Arguments](/docs/manual/latest/bind-to-js-function#fixed-arguments)
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* [`@as` decorator and variants](variant.md#valid-as-payloads)

‎misc_docs/syntax/decorator_tag.mdx

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---
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id: "tag-decorator"
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keywords: ["tag", "decorator"]
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name: "@tag"
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summary: "This is the `@tag` decorator."
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category: "decorators"
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---
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The `@tag` decorator is used to customize the discriminator for tagged variants.
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<CodeTab labels={["ReScript", "JS Output"]}>
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```res
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type mood = Happy({level: int}) | Sad({level: int})
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@tag("kind")
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type mood2 = Happy({level: int}) | Sad({level: int})
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let mood: mood = Happy({level: 10})
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let mood2: mood2 = Happy({level: 11})
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```
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```js
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let mood = {
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TAG: "Happy",
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level: 10
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};
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let mood2 = {
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kind: "Happy",
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level: 11
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};
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```
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</CodeTab>
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Notice the different discriminators in the JS output: `TAG` in `mood` vs `kind` in `mood2`.
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Read more about [using `@tag` with variants](variant.md#tagged-variants).
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### References
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* [Using `@tag` with variants](variant.md#tagged-variants)

‎misc_docs/syntax/language_spreads.mdx

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---
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id: "spreads"
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keywords: ["spread", "record", "variant", "polymorphic", "array", "list", "function", "partial"]
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name: "..."
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summary: "This is the `...` syntax."
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category: "languageconstructs"
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---
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A `spread` is three dots in a row: `...`. Spreads have many different uses in ReScript depending on in which context it is used.
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## Record definitions
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> Available in v10+
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Spreads can be used to copy fields from one record definition into another.
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```res
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type a = {
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id: string,
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name: string,
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}
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type b = {
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age: int
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}
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type c = {
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...a,
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...b,
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active: bool
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}
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```
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Read more about [record type spreads here](record.md#record-type-spread).
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## Record immutable update
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Spreads can be used for immutable updates of records:
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```res
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let meNextYear = {...me, age: me.age + 1}
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```
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Read more about [record immutable updates here](record.md#immutable-update).
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## Variant definitions
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> Available in v11+
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Spreads can be used to copy constructors from one variant definition to another.
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```res
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type a = One | Two | Three
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type b = | ...a | Four | Five
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// b is now One | Two | Three | Four | Five
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```
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Read more about [variant type spreads](variant.md#variant-type-spreads) here.
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## Variant pattern matching
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> Available in v12+
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You can refine the type of a variant by spreading compatible a variant when pattern matching:
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```res
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type pets = Cat | Dog
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type fish = Cod | Salmon
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type animals = | ...pets | ...fish
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let isPet = (animal: animals) => {
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switch animal {
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| ...dog => Console.log("A dog!")
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| _ => Console.log("Not a dog...")
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}
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}
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```
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Read more about [variant type spreads in pattern matching](pattern-matching-destructuring.md#match-on-subtype-variants).
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## Polymorphic variant pattern matching
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You can refine compatible polymorphic variants when pattern matching:
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```res
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type red = [#Ruby | #Redwood | #Rust]
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type blue = [#Sapphire | #Neon | #Navy]
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// Contains all constructors of red and blue.
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// Also adds #Papayawhip
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type color = [red | blue | #Papayawhip]
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let myColor: color = #Ruby
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switch myColor {
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| #...blue => Console.log("This blue-ish")
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| #...red => Console.log("This red-ish")
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| other => Console.log2("Other color than red and blue: ", other)
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}
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```
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Read more about [pattern matching and polymorphic variants](polymorphic-variant.md#combine-types-and-pattern-match).
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## List immutable update
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Spreads can be used for immutable updates of lists:
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```res
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let prepended = list{1, ...someOtherList}
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// You can spread several lists, but it's O(n) so avoid it if possible
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let multiple = list{1, ...prepended, ...anotherList}
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```
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Read more about [immutable list updates](array-and-list.md#immutable-prepend) here.
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## List pattern matching
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Spreads can be used when pattern matching on lists:
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```res
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let rec printStudents = (students) => {
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switch students {
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| list{} => () // done
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| list{student} => Console.log("Last student: " ++ student)
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| list{student1, ...otherStudents} =>
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Console.log(student1)
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printStudents(otherStudents)
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}
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}
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printStudents(list{"Jane", "Harvey", "Patrick"})
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```
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Read more about [pattern matching on lists](pattern-matching-destructuring.md#match-on-list).
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## Array immutable update
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> Available in v11+
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You can use spreads to add the contents of one array to another, just like in JavaScript:
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```res
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let firstArray = [1, 2, 3]
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let secondArray = [...firstArray, 4, 5]
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```
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Read more about [array spreads](array-and-list.md#array-spreads).
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## Partial application of functions
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> Available in v11+ (uncurried mode)
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You can partially apply a function using the spread syntax. Partially applying a function will return a new function taking only the arguments that wasn't applied partially.
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```res
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let add = (a, b) => a + b
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let addFive = add(5, ...)
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```
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Read more about [partial application of functions](function.md#partial-application).
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### References
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* [Record type spreads](record.md#record-type-spread)
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* [Record immutable updates](record.md#immutable-update)
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* [Variant type spreads](variant.md#variant-type-spreads)
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* [Variant type spreads in pattern matching](pattern-matching-destructuring.md#match-on-subtype-variants)
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* [Pattern matching and polymorphic variants](polymorphic-variant.md#combine-types-and-pattern-match)
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* [List immutable updates](array-and-list.md#immutable-prepend)
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* [List pattern matching](pattern-matching-destructuring.md#match-on-list)
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* [Array spreads](array-and-list.md#array-spreads)
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* [Partial application of functions](function.md#partial-application)

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