proposal-pattern-matching VS TypeScript

Note, however, that there is a proposal to add pattern matching to JS.

There's an ECMAScript proposal that is in the works to add this feature to the language! It's going to look something like this.

More importantly, TypeScript typically commits to build things into itself when the proposal in JavaScript reaches Stage 3. The pattern matching proposal in JavaScript is Stage 1, but depends on many other proposals as well that may or may not need to be at Stage 3 as well for it to work. This particular proposal is interested on pattern matching on JavaScript Objects and other primitives, just like Python does with it’s native primitives. These are also dynamic types which helps in some areas, but makes it harder than others. Additionally, the JavaScript type annotations proposal needs to possibly account for this. So it’s going to be awhile. Like many years.

For true™ functional programming in JS, native pattern matching and partial function application are missing (at least for now: 1, 2). For proper OOP, it lacks real interfaces and compile-time dependency injection.

The proposal for pattern matching syntax seems more akin to what they're looking for.

https://github.com/tc39/proposal-pattern-matching

There's a proposal to add something like that to JavaScript but it's been stuck in limbo since 2017 although there are libraries like ts-pattern which implement it already.

I'll admit, it is easy to assert that the TypeScript language should not be involved in the matters of packages but I also wonder if we're moving towards a point where interfaces will be as common as namespaces and whether or not it would be sensible for the language to incorporate such type assertions into the language formally, after all, it already compiles to various forms of JavaScript and there is a stage 1 proposal submitted to the TC39 committee to give JavaScript pattern matching. If adopted, wouldn't it make sense to allow TypeScript to compile a type into a type guard for the native JavaScript pattern matcher?

Both are active tc39 proposals :)

https://github.com/tc39/proposal-pipeline-operator - Stage 2

https://github.com/tc39/proposal-pattern-matching - Stage 1

Hopefully we get both in the next couple of years.

We often add promising TC39 proposals into Civet so people can experiment without waiting.

We've added https://github.com/tc39/proposal-pipeline-operator, a variant of https://github.com/tc39/proposal-pattern-matching, a variant of https://github.com/tc39/proposal-string-dedent and others.

Since our goal is to be 99% compatible with ES we'll need to accommodate any proposals that become standard and pick up anything TC39 leaves on the table (rest parameters in any position, etc.)

Regular expressions are part of the language, so it's not so unreasonable that TypeScript should parse them and take their semantics into account. Indeed, TypeScript 5.5 will include [new support for syntax checking of regular expressions](https://github.com/microsoft/TypeScript/pull/55600), and presumably they'll eventually be able to solve the problem the GP highlighted on top of those foundations.

Dedicated syntax for creating unique subsets of a type that denote a particular refinement is a longstanding ask[2] - and very useful, we've experimented with implementations.[3]

I don't think it has any relation to runtime type checking at all. It's refinement types, [4] or newtypes[5] depending on the details and how you shape it.

[1] https://github.com/microsoft/TypeScript/blob/main/src/compil...

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