"Powered by WebAssembly": Other languages can compile to WebAssembly as well as other targets. Why is limiting to only one target considered a good thing? What does it buy you? (if it's unique that it has a GC, or if the GC is performant that may be a good reason. Advertise it!).
The vision of bringing ideas from functional/academic languages into the mainstream is noble. But the language features seem very run of the mill? I don't understand what it's referring to.
Comments on the standard library:
* Reference docs should make more clear the differences between Array and List. I assume Array is a fixed size contiguous array of data with constant time get and set? And List is an immutable linked list. But I had to wander around docs and implementation to reach that conclusion.
* Reference docs should probably mention List syntax in the List docs. Ditto for Arrays. You normally expect to see that at the top of the page, vs as a surprising comment "An alias for normal syntactic array access, i.e. array[n].". It's hard to tell what is a library feature vs primitive to the language.
* {Array,List}.append: In most languages I have used append means to append a single element (or in Go's case it is variadic). I would probably rename this to concat and remove the existing concat function.
* What is the benefit to having a separate Stack type vs adding convenience functions to List?
let List.push = (value, list) => list.
let List.pop = (list) => (value, list).