> > > Traditional hash tables are imperative data structures, and Lisp code (or Scheme code, at least) typically does not use them because of this. Association

> > > Traditional hash tables are imperative data structures, and Lisp code (or Scheme code, at least) typically does not use them because of this. Association lists, which can be represented as literals, are persistent and {snip} > > I don't understand that. > Introducing state into programs makes them harder to reason about, thus Scheme programmers generally discourage the use of mutable data structures when a persistent data structure would have worked. Oh, maybe you typoed and meant to say that traditional hashtables are mutable data structures? In that case, I see what you mean; in Clojure, hashmaps, vectors, sets, and lists are all immutable and persistent. In Scheme, which data structures are persistent, or mutable/immutable? > The way alists are used, only the first pair to contain the desired key is considered. Ok, I see now. The function creates a hashmap from an alist. > I learned that people reach for mutable hash tables far too frequently when there are better options available. {raises hand} They're very easy to work with. In Clojure, I found myself doing extra work to work around the immutability. I'm sure it's a benefit for larger and multithreaded programs, but mine were neither. > What languages even have literal syntax for sets? I can't think of any, but I'd like to know. Clojure and Python. I suppose I could live without literal set syntax, but hashmap/hashtable syntax is extremely handy.