I'm very sympathetic to the problem. I'm working on Dark (https://darklang.com) which is a functional language, explicitly because we believe that functional languages are easier to learn, understand and provide great tooling for.
It seems to me there's a lot of focus on syntax, and I don't think they've gotten to a great place. For example:
(this Int).square | Int = this.*(this)
impl Int {
fn square (self) -> Int {
self * self
}
}
In Dark, we use piping heavily to get the benefits of the dot-syntax. In particular, it can be type directed:
8 |> Int::square |> Int::log 2
For the problem of "which parameter" - our IDE shows parameter names when your cursor is in a position to type the next parameter, so you know what you're adding it is. We also show the parameter names when your cursor is in the completed argument so you know what parameter it is. (I couldn't see if Keli did this, it might not be possible in modern editors).