Of course, they're linked list, they have an inherent order. Once you understand how they behave, you understand where the abstraction leaks.
def foo(x, opt1: opt1, opt2: opt2)
Of course, we could then say "let's allow a default value to be given when pattern matching keyword lists". The problem is that no other pattern works like this and it would be inconsistent.
I think optional arguments are fundamentally incompatible with pattern matching (in Elixir). I understand why we would want that but, if we did have it, we would be adding tons of complexity and it would stand out as a sore thumb. I am also wary of going towards the same direction as Ruby and Python which have quite complex argument handling (albeit we have slightly different feature sets).
But i doubt it would be an urgent thing to change.
Tldr: add named arguments (optional). You can call with anon names, in which case it is positional as it is today. If you use named arguments to call, you have to use them in the order they have been declared, just like with positional, but you _can_ omit some. These get the default value.
There are ofc combinations that could be allowed, like anon until the first optional one, whatever.
It was part of this post, but don't it was a solution to a different problem kinda (and kinda not technically) https://faultlore.com/blah/defaults-affect-inference/