> Closures are an implementation detail.
Except when they are not there done properly (cough cough Python), it not so fun doing functional programming.
> Tail call elimination is just the right way to implement tail calls in a strict language.
Well Erlang is not strict and has tail call elimination. Because of lack immutability, recursion is used. Without tail call elimination recursion will blow the stack.
> Variables don't “mutate”, they are substituted with other expressions. What imperative languages have is “assignables”.
Yes they do. X=X+1 -- Variable mutated. Like it or not that is the bread and butter of programming. Unless someone did strictly functional programming and math. Then I can see how they'd be very confused by that statement.
There is also immutable vs mutable data. For example both Erlang and Elixir have immutable data. But Elixir has mutable variable, while Erlang doesn't.
As for assignables, I've never heard that word. I went to the standard 4 year CS program. Seemingly did a regular curriculum. Is that a translation from another langauge or a functional programming terminology?
> Functional programs have plenty of state - which changes over time.
Some have more, some less. Minimizing means making it explicit, passing it around, using immutable data. As opposed to say sticking it in a large object instance in a global singleton and then everything calls 100 something methods to mutate it.
> What (technical!) definition “declarative” are you using?
The point I think is, it is just as technical as "functional" is. It has a bit of a "No True Scotsman" thing going for it.
But as a heuristic think maybe about when you'd use patern matching to destructure something vs say a nested set of if and elses.
