Type signatures potentially confusing

[paldepind]

I like how the types here are specified in a more Flow/TypeScript way. I think that type notation is a better fit for JavaScript and I think it'll be more friendly to a wider range of JavaScript developers.

However, in one aspect the current types can be confusing to TypeScript/Flow users. In both TypeScript and Flow this notation

(a: A) => B

denotes a function with an argument named a of a type named A that returns a value of type B. If we leave out the A we have this:

(a) => B

This denotes a function with an argument named a but where the type is unspecified (the Flow/TypeScript compiler will try to infer it).

Consider this code from the specification:

Group<T> {
  invert: (T) => T
}

Here the spec wants to say that invert takes an argument of type T and returns an argument of type T. But, in TypeScript/Flow the above syntax actually means that invert takes an argument with name T but it doesn't say anything about the type of the argument to invert. For the above to make more sense for at TypeScript/Flow user we could instead write:

Group<T> {
  invert: (t: T) => T
}

I know the above is a bit more verbose, but it makes more sense to TypeScript/Flow users. I understand that the difference between the two doesn't seem huge but when you're very used to reading TypeScript/Flow types the current types looks "off".

Thank you for your consideration!

[rpominov]

Flow actually allows to omit argument names in function types, e.g. A => B is valid and equivalent to (a: A) => B. And I, for one, always write it as A => B at work where we use Flow, so I kinda used to it.

I don't have a strong opinion on this one too. It makes sense if it'll make signatures more familiar, but will also add a bit of a noise.

[paldepind]

I see. I had no idea. I thought Flow was similar to TypeScript in this regard. Then what I wrote above only applies to TypeScript.

If you feel that changing (A) => B to (a: A) => B adds too much noise then an alternative would be to have small note for TypeScript users that explains the difference.

[rpominov]

Adding a note seems to me like a right move. Done it.