I know naming is hard, but this is getting out of hand. Don't say you're a Lisp when you're clearly not. Say Lisp-inspired. Don't use the term 'modern Lisp', 9/10 it's signaling the wrong thing.
Saying that a language isn't a "real lisp" because it doesn't use cons cells is like saying a map implemented using a red-black tree isn't a "real" map because it doesn't use an array of nodes.
> Is the language somehow less useful
It may in fact be the most generally useful programming system in the world.
But does it have to be misleadingly named?
Would you make a four-wheeled bicycle and call it a "skateboard"?
> saying a map implemented using a red-black tree isn't a "real" map
Rather, it's like writing a map using an array of nodes, and then calling it "red black tree" and using identifiers like rbtree_t and rbtree_node_t all over the code, complete with a rbtree_lower_bound function that calls bsearch, followed by a linear scan to find the lowest duplicate key. Why? Because all the popular maps use red-black trees and the designer doesn't understand what that actually is, believing it to be a synonym for any ordered map.
Lisp is not abstract, like "map"; it started as the name of a concrete computer program with a reference manual describing specific features. It spawned descendant systems and imitations. Those which are too far from the original concept aren't Lisp, simple as that.
"Lisp" is an implementation word, not an abstraction word.
Lisp is a specific implementation of symbolic and list processing with specific shapes of data structures, names of functions and their semantics, treatment of Boolean conditions, syntax, and everything else.
Another implementation of symbolic processing, no matter how well or how badly it works, is something else.
People who make Algol-like languages understand this.
Wirth made some very similar languages yet prudently gave them different names. The result is that anyone who says that Oberon is Pacal or that Pascal is Modula 2 is promptly and correctly regarded as an idiot.
I think it's signalling exactly the right thing. We know exactly what to expect when someone claims they've made a "modern Lisp". That phrase has come to mean "something with parentheses that demonstrates that its author doesn't understand Lisp at all."
# A simple fizz buzz example
(loop [i :range [1 101] :let [fizz (zero? (% i 3)) buzz (zero? (% i 5))]] (print (cond (and fizz buzz) "fizzbuzz" fizz "fizz" buzz "buzz" i)))
Is this not lisp?
Another criteria used is homoiconicity.
I think the argument is about if a language satisfies the historical definition of "Lisp" rathen than being a Lisp-inspired language with parens.
And no, Clojure isn't a Lisp. Perhaps it would be appropriate to say that Janet is "a Clojure".
With that said, the underlying datastructures don't actually deter from the fact that you can quote and unquote what appear to be lists, and it walks and quacks more or less like a lisp (like clojure, as a sibling pointed out), so I don't actually mind.
In fact, Janet just might be my favorite scripting language, even if I haven't had occasion to use it for anything impressive yet.