Clojure Koans Walkthrough

1. Introduction
2. Lists
3. Vectors
4. Sets
5. Maps
6. Functions
7. Conditionals
8. Higher Order Functions
9. Runtime Polymorphism
10. Lazy Sequences
11. Sequence Comprehensions
12. Creating Functions
13. Recursion
14. Destructuring
15. Refs
16. Atoms
17. Macros
18. Datatypes
19. Java Interop
20. Partition

Recommended Books

• ← Maps
• Conditionals →

6. Functions - Koans Walkthrough

This video covers functions. Clojure has amazing support for first-class functions, and among the most concise syntax for anonymous functions of any language.

Here is the 06_functions.clj source code:

(defn multiply-by-ten [n]
  (* 10 n))

(defn square [n] (* n n))

(meditations
  "Functions are often defined before they are used"
  (= __ (multiply-by-ten 2))

  "But they can also be defined inline"
  (= __ ((fn [n] (* __ n)) 2))

  "Or using even shorter syntax"
  (= __ (#(* 15 %) __))

  "Short anonymous functions may take multiple arguments"
  (= __ (#(+ %1 %2 %3) 4 5 6))

  "One function can beget another"
  (= __ ((fn []
           ((fn [a b] (__ a b))
            4 5))))

  "Higher-order functions take function arguments"
  (= 25 (___
         (fn [n] (* n n))))

  "But they are often better written using the names of functions"
  (= 25 (___ square)))