Programming Clojure, 2nd Edition

Functions

In Clojure, a function call is simply a list whose first element resolves to a function. For example, this call to str concatenates its arguments to create a string:

(str "hello" " " "world")
-> "hello world"

Function names are typically hyphenated, as in clear-agent-errors. If a function is a predicate, then by convention its name should end with a question mark. As an example, the following predicates test the type of their argument, and all end with a question mark:

(string? "hello")
-> true

(keyword? :hello)
-> true

(symbol? 'hello)
-> true

To define your own functions, use defn:

(defn name doc-string? attr-map? [params*] body)

The attr-map associates metadata with the function’s var. It’s ...