My 5c is that we should avoid reusing that trick. In my view it just makes the code more complicated and hard to follow for little gain.

There are currently about 60 files that use querySelector. Adding a safe version for each element type could result in significant duplication.

Well, using include creates that same duplication in the compiler anyway (include is a copy paste in the compiler). It's not in the ReScript source files, but it'll be the same duplication in the output. And the output will probably be worse and harder to follow.

What about just using functions? Some internal function that takes a classifier or similar for each use case. Then we can just partially apply that same function in all relevant places. If we worry about duplication.

I don't think I mind duplication, but in this case, there is practical side.
I would add about 60 helpers for type safe querySelector access and would need to add those in 60 files.
The include trick makes this that second part easier. Especially if we revisit bindings.

What about just using functions? Some internal function that takes a classifier or similar for each use case. Then we can just partially apply that same function in all relevant places. If we worry about duplication.

Could you give an example maybe?

Just so I understand correctly - you mean each of these 60 files get 60 variations of querySelector? So we have 3600 bindings to queryselector essentially?

Yeah, so you have document.querySelector which returns an element.
In this first example I've added a querySelector_htmlCanvasElement helper to the document module.
But any HTMLElement interface has the querySelector method as well, because of the Element inheritance.

The way it is currently set up is that HTMLButtonElement for example, currently has a @send querySelector taking an htmlButtonElement as first argument. This is to avoid that the user would need to "downcast" the htmlButtonElement to an element before they can use querySelector.

@zth I've added an example to illustrate this in 374f47c