Question

The API Cheatsheet section on Lists seems to indicate that '() is a list constructor, just like (list), but I’ve found that in practice they’re not exactly the same. For example, given:

(def foo "a")
(def bar "b")
(def zip "c")

The following statement:

(apply str '(foo bar zip))

produces the output “foobarzip”, which I wouldn’t expect.

But the supposedly equivalent:

(apply str (list foo bar zip))

produces “abc”, as I’d expect.

What’s going on here? If there’s a “shorthand” for a list in Clojure (like {} for maps and [] for vectors), what is it?

Answer 1

In lisps, ' (like quote) quotes its arguments, i.e. preserves them pretty much exactly as written in their s-exp form, including not evaluating anything within.

To put it another way '(foo bar zip) creates a list containing the symbols foo, bar, zip; while (list foo bar zip) creates a list containing the values of foo, bar, zip. In the first case, str will be converting the symbols themselves to strings and then concatenating them.

As a demonstration of this:

=> (def foo "a")
=> (type (first '(foo)))
clojure.lang.Symbol
=> (type (first (list foo))) 
java.lang.String