I am not suggesting that the svelte.each() call be moved into a library; I'm proposing that the callsite is trivial to identify in the AST. Svelte compiler could then do the same thing that it does now.

Grammar enforces where a grammar construct is allowed to exist. A custom grammar can be very restrictive (which it is, to great effect, in Svelte's case).

If we reuse JS grammar, then that comes with expectations of what should semantically work. For example something as simple as `$ = svelte.each` might evade a not-sufficiently-smart compiler. Or maybe `console.log(svelte.each(...))` might mis-compile because nobody ever thought to handle that case.

Having used systems with compile-time grammar constructs that look like runtime constructs, I can tell you that having your expectations about semantics being changed from under your feet can be a very frustrating experience.

Just to be clear, I am NOT saying that Svelte needed to do this. But merely suggesting options for discussion and learning.

[1]: https://github.com/jeswin-unmaintained/isotropy-ast-analyzer... - Here's for instance, some code I wrote for analyzing a JS sort expression. You'd think it'd take just a few hours, until you get to it. Btw, it uses an AST analysis framework I wrote called chimpanzee - it has only one user though. :) https://github.com/jeswin/chimpanzee

In such a case, I think it's less confusing at the end of the day to just have a custom DSL for looping so that there's no clashing with its list of arbitrary limitations.