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BinaryPattern => BinaryMatchPattern
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‎experimental/pattern-matching-examples.md

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# AST examples of [Pattern Matching ESTree Proposal](proposal-pattern-matching-estree)
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Note: The `ExpressionStatement` and `Program` is omitted in the examples.
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## 1. Object Match Pattern and "else" Match Clause
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```js
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match (x) {
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when ({ colour: "#000000" }) { "yes" }
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else {
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"no"
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}
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}
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```
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```jsonc
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{
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"type": "MatchExpression",
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"discriminant": { "type": "Identifier", "name": "x" },
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"id": null,
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"clauses": [{
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"type": "MatchClause",
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"test": {
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"type": "ObjectMatchPattern",
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"properties": [{
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"type": "Properties",
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"key": { "type": "StringLiteral", "value": "colour" },
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"value": { "type": "StringLiteral", "value": "#000000" }
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}]
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},
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"consequent": {
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"type": "BlockStatement",
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"body": [{
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"type": "ExpressionStatement",
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"expression": { "type": "StringLiteral", "value": "yes" }
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}]
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},
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"guard": null,
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"id": null
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}, {
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"type": "MatchClause",
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"test": null,
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"consequent": {
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"type": "BlockStatement",
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"body": [{
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"type": "ExpressionStatement",
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"expression": { "type": "StringLiteral", "value": "no" }
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}]
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},
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"guard": null,
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"id": null
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}]
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}
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```
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## 2. Matchable `as` RHS, Array Match Pattern and Null Match Pattern
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```js
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match (f()) as [x, y] {
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when ([_, _, 200]) { "foo"; }
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else {
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process(x, y)
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}
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}
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```
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```jsonc
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{
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"type": "MatchExpression",
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"discriminant": {
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"type": "CallExpression",
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"callee": { "type": "Identifier", "name": "f" },
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"arguments": []
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},
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"id": {
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"type": "ArrayPattern",
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"elements": [
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{ "type": "Identifier", "name": "x" },
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{ "type": "Identifier", "name": "y" }
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]
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},
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"clauses": [{
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"type": "MatchClause",
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"test": {
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"type": "ArrayMatchPattern",
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"elements": [
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{ "type": "NullMatchPattern" },
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{ "type": "NullMatchPattern" },
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{ "type": "Literal", "value": 20 }
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]
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},
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"consequent": {
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"type": "BlockStatement",
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"body": [{
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"type": "ExpressionStatement",
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"expression": { "type": "StringLiteral", "value": "foo" }
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}]
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},
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"guard": null,
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"id": null
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}, {
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"type": "MatchClause",
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"test": null,
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"consequent": {
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"type": "BlockStatement",
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"body": [{
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"type": "CallExpression",
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"callee": { "type": "Identifier", "name": "process" },
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"arguments": [
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{ "type": "Identifier", "name": "x" },
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{ "type": "Identifier", "name": "y" }
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]
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}]
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},
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"guard": null,
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"id": null
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}]
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}
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```
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## 3. Match Clause "as" RHS and guard condition
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```js
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match (x) {
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when (/(?<x>\d+)/) as { groups: { y } } if (isEmpty(y)) {}
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}
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```
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```jsonc
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{
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"type": "MatchExpression",
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"discriminant": { "type": "Identifier", "name": "x" },
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"id": null,
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"clauses": [{
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"type": "MatchClause",
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"test": {
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"type": "Literal",
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"regex": { "pattern": "(?<x>\\d+)", "flags": "" }
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},
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"consequent": {
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"type": "BlockStatement",
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"body": []
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},
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"guard": {
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"type": "CallExpression",
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"callee": { "type": "Identifier", "name": "isEmpty" },
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"arguments": [
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{ "type": "Identifier", "name": "y" }
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]
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},
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"id": {
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"type": "ObjectPattern",
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"properties": [{
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"type": "Property",
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"key": { "type": "Identifier", "name": "groups" },
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"value": {
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"type": "ObjectPattern",
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"properties": [{
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"type": "Property",
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"key": { "type": "Identifier", "name": "y" }
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}]
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}
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}]
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}
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}]
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}
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```
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## 4 "if" Match Clause and Binary Match Pattern
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```js
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match (x) {
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if(isEmpty(x)) {}
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when({ status: 200 | 201 }) {}
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}
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```
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```jsonc
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{
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"type": "MatchExpression",
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"discriminant": { "type": "Identifier", "name": "x" },
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"id": null,
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"clauses": [{
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"type": "MatchClause",
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"test": {
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"type": "Literal",
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"regex": { "pattern": "(?<x>\\d+)", "flags": "" }
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},
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"consequent": {
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"type": "BlockStatement",
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"body": []
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},
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"guard": {
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"type": "CallExpression",
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"callee": { "type": "Identifier", "name": "isEmpty" },
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"arguments": [{ "type": "Identifier", "name": "x" }]
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},
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"id": null,
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}, {
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"type": "MatchClause",
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"test": {
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"type": "ObjectMatchPattern",
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"properties": [{
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"type": "Properties",
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"key": { "type": "StringLiteral", "value": "status" },
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"value": {
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"type": "BinaryMatchPattern",
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"operator": "or",
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"left": { "type": "Literal", "value": 200 },
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"right": { "type": "Literal", "value": 201 }
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}
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}]
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},
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"consequent": {
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"type": "BlockStatement",
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"body": []
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},
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"guard": null,
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"id": null
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}]
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}
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```
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## 5 RegExp as Match Pattern, "with" additional Match Pattern and As Match Pattern
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```js
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match (x) {
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when ({
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input: (/(?<x>\d+(?<d>[NSEW]))/ with [_, 200, _]) as { groups: { d } }
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}) {}
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}
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```
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```jsonc
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{
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"type": "MatchExpression",
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"discriminant": { "type": "Identifier", "name": "x" },
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"id": null,
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"clauses": [{
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"type": "MatchClause",
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"test": {
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"type": "ObjectMatchPattern",
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"properties": [{
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"type": "Properties",
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"key": { "type": "StringLiteral", "value": "input" },
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"value": {
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"type": "AsMatchPattern",
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"test": {
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"type": "BinaryMatchPattern",
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"operator": "with",
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"left": {
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"type": "Literal",
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"regex": { "pattern": "(?<x>\\d+(?<d>[NSEW]))", "flags": "" }
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},
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"right": {
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"type": "ArrayMatchPattern",
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"elements": [
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{ "type": "NullMatchPattern" },
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{ "type": "Literal", "value": 20 },
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{ "type": "NullMatchPattern" }
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]
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}
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},
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"id": {
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"type": "ObjectPattern",
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"properties": [{
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"type": "Property",
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"key": { "type": "Identifier", "name": "groups" },
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"value": {
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"type": "ObjectPattern",
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"properties": [{
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"type": "Property",
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"key": { "type": "Identifier", "name": "d" }
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}]
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}
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}]
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}
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}
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}]
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},
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"consequent": {
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"type": "BlockStatement",
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"body": []
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},
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"guard": null,
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"id": null
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}]
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}
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```
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## 6 Expression Match Pattern
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```js
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match (token) {
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when (^LF | ^CR) {}
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}
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```
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```jsonc
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{
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"type": "MatchExpression",
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"discriminant": { "type": "Identifier", "name": "x" },
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"id": null,
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"clauses": [{
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"type": "MatchClause",
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"test": {
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"type": "BinaryMatchPattern",
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"operator": "or",
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"left": {
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"type": "ExpressionMatchPattern",
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"expression": { "type": "Identifier", "name": "LF" }
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},
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"right": {
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"type": "ExpressionMatchPattern",
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"expression": { "type": "Identifier", "name": "CR" }
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}
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},
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"consequent": {
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"type": "BlockStatement",
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"body": []
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},
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"guard": null,
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"id": null
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}]
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}
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```
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## 7. Expression Match Pattern and computed Object Match Pattern
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```js
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match (action) {
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when (["take", ...{ [computed]: -200 }]) {}
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}
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```
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```jsonc
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{
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"type": "MatchExpression",
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"discriminant": { "type": "Identifier", "name": "action" },
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"id": null,
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"clauses": [{
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"type": "MatchClause",
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"test": {
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"type": "ArrayMatchPattern",
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"elements": [
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{ "type": "Literal", "value": "take" },
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{
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"type": "RestMatchElement",
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"argument": {
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"type": "ObjectMatchPattern",
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"properties": [{
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"type": "Property",
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"key": { "type": "Identifier", "name": "computed" },
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"computed": true,
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"value": {
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"type": "UnaryExpression",
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"operator": "-",
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"prefix": true,
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"argument": { "type": "Literal", "value": 200 }
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}
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}]
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}
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}]
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},
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"consequent": {
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"type": "BlockStatement",
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"body": []
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},
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"guard": null,
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"id": null
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}]
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}
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```
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[proposal-pattern-matching-estree]: https://github.com/JLHwung/estree/proposal-pattern-matching/

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