Overview of Clojure Features

### What does it mean that Clojure collections are “persistent”? - [x] Updates return a new value and reuse structure from the old value instead of mutating it in place. - [ ] Collections automatically persist to disk on every update. - [ ] Values cannot be garbage-collected. - [ ] Maps can only use keywords as keys. > **Explanation:** Persistent data structures are immutable. “Persistent” here refers to structural sharing across versions, not persistence to storage. ### What does “functions are first-class” allow you to do? - [x] Pass functions as arguments, return them, and store them in data structures. - [ ] Use functions only at the top level of a file. - [ ] Define functions without namespaces. - [ ] Avoid using collections. > **Explanation:** Treating functions as values is what makes higher-order patterns like `map`, `reduce`, and function composition feel natural. ### What’s the most important difference between a macro and a function? - [x] A macro transforms code forms before evaluation; a function evaluates its arguments and operates on values. - [ ] A macro is always faster than a function. - [ ] A macro can only be used for concurrency. - [ ] A macro cannot call other functions. > **Explanation:** Macros operate on the unevaluated structure of code. Prefer functions first; reach for macros when you truly need a new syntactic shape or control structure.