[ubercow]

Clojure's "killer feature" for me is the by-default persistent data structures.

Are there any other functional languages out there with similar features? Lisp or otherwise.

[lilactown]

Erlang/Elixir also is immutable & persistent by default.

[retrogradeorbit]

It is immutable and persistent, but not with the same performance characteristics. It lacks Bagwell's data structures that allow structural sharing. Take a 10 million item list in elixir and 'change' (return a new) the 5 millionth element. Time how long it takes. Do the same with clojure. Compare.

[ramchip]

That was true a few years ago, but not anymore: https://medium.com/@jlouis666/breaking-erlang-maps-1-31952b8...

(You would have to use a map though, the native lists are still plain old lists)

[mintplant]

In Haskell, data structures are immutable, persistent, and use structural sharing by default.

[pmarreck]

Elixir has that, and you can't even drop into Java/JVM mode to violate it! ;)

Haskell as well, I believe.

[runT1ME]

Scala has a collections library that heavily emphasizes immutable/persistent data sructures. You aren't forces to use them but it is idiomatic Scala to be "pure"/non mutating.