But you can use them as evidence that tsc is not working as it "should". Then go ahead and fix tsc Or spec or both as needed.

Without the specs, there is no way to tell if tac is behaving as developers intended it

It's not doing what I expect. Oh? Change the spec

It's not doing what I expect. Oh? Change the code

How is that different from now?

Allows competing implementations and saves TS from MSFT

Right now:

1.It's not doing what I expect.

2.Is it intentional behavior or a bug?

3. Let's ask on github/reddit etc

With Special:

1. It is not doing what I expect

2. Is this a spec issue or code issue?

3. Let's check spec.

4a. "Working as specified". Shit. Hope spec improves in future versions

4b. It is not working as spec says. Let's file a bug on tsc.

And that is the difference.

The real rub is in step 4: it is not always easy to determine what the spec means. And then you're basically back to "let's ask on github/reddit etc."

Just because the comprehensiveness of something is on a spectrum is not a reason to just not bother and have none at all.

Also, when done well a spec is a great way to learn & understand the language too. http://golang.org/ref/spec is so much more usable than Typescript's docs.

I agree that specifications are useful. I also think they're often presented as a panacea. It is important to acknowledge that they're a tool, with pros and cons, like any tool. The existence of a specification does not immediately mean that any and all ambiguities are resolved.

Still doesn’t seem like much a difference. If you run into 4a you still file an issue somewhere.

If an implementation isn't doing what you expect, is it just an issue with that single implementation? A problem with all implementations? A problem with what you expect? If another implementation does do what you expect is it correct or just lucky?

A spec resolves such discrepancies. Indeed, the spec may be where the problem is, but once the spec is corrected then implementations know what they must do. Absent of a spec, who knows?

And such a spec can be

1) a reference implementation,

2) written in natural language, or

3) written as formal semantics

#1 is the same as the current situation. With #2, you might get a bit closer but natural language has many ambiguities and idiosyncrasies that can render it useless in various situations.

You can try to define formal semantics, but that is not only hard to create, it's also hard to translate into an implementation, adding significant overhead in both parts of the process. And there can still be bugs, and there can still be edge cases with undefined behavior.

Code, called implementation here, is a specification written in a certain grammar that is executed.

You want 'evidence' tsc is not working as it should, by writting a duplicated less specifying specification that would sometimes conflict with the typescript one.

It make me remember the people that wanted to specify everything and generate implementation from it: that called a programming language.

Code is meant for machine.

Specification is meant for compiler author. Writing one of them is easier than otht

They are not mutually exclusive. Code identifies a class of language. Specification identifies something that is conveyed through language. Specification can be provided in code.

In fact, while poorly named, what we call testing is actually specification. A test suite specifies for software authors what a program is intended to do and how it is intended to be used. Of course, as a nice side bonus, because the specification is delivered in code the documentation can be validated for truthfulness against an implementation by machine.

But at least formal methods tools can be applied directly to the specification, to show properties like "well, if you carve out this subset of TypeScript, you have something you can safely eval()" or "you can never have type errors with this usage of this construct in this way."

> "well, if you carve out this subset of TypeScript, you have something you can safely eval()" or "you can never have type errors with this usage of this construct in this way."

This kind of certainty is very at odds with TypeScript's design philosophy and the way it (necessarily) works. Because it's overlaid on JavaScript, and JavaScript is wildly dynamic (Proxies, prototype modification, etc), almost nothing is known with absolute certainty. To deal with that, TypeScript makes a lot of "optimistic" assumptions, but holds them lightly (i.e. its assumptions may cause type checks to pass when they shouldn't, but it's not going to lean on them for anything that could really blow up if they're wrong)

IMO it strikes a very good balance given the constraints - not criticizing the designers at all - but TypeScript has to be treated differently than other statically typed languages might be, because nearly everything it knows/says is just a "probably"

> But at least formal methods tools can be applied directly to the specification

What makes you think that? For example for C language it has been significant effort to translate the specification to something analyzable by tools

Neither are programs, tests, or type definitions, but these are generally still valuable things to have.