Hmm. Implemented on a custom type that wraps []T, so you have to create a List to get the methods, meaning more boilerplate (a common theme in Go); eager, like JavaScript’s Array methods rather than like the iterator methods in Rust or most/all functional programming languages; and since methods can’t have generics (which really surprised me in the Go generics proposal), Map() can only work on the same type (T → T, rather than T → U), and Reduce()’s output type is a generic parameter on the list, so you can only ever reduce to one type (unless you deconstruct and reconstruct the List) which must be specified at instantiation time.

As one who works mostly in Rust and JavaScript and is passingly familiar with Go (I used it for a couple of projects eight and nine years ago), these seem some pretty severe limitations.

Rust’s trait-based iterator system is delightful, so that you can map, filter, reduce, &c. on any iterator, lazily, and even define an extension trait to define your own methods on any iterator, thereafter accessible by just importing that trait.

In the end, I think the current scope of generics and interfaces won’t be enough to produce any feeling other than “shoehorned” for this functional style in Go. It’s just not a style that works well in all types of programming languages.