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

• ← Refs
• Macros →

16. Atoms - Koans Walkthrough

This video introduces atoms, which are like refs, but provide swap! and compare-and-set! to mutate an atom's value without having to use a dosync transaction.

Here is the 16_atoms.clj source code:

(def atomic-clock (atom 0))

(meditations
  "Atoms are like refs"
  (= __ @atomic-clock)

  "You can change at the swap meet"
  (= __ (do
          (swap! atomic-clock inc)
          @atomic-clock))

  "Keep taxes out of this: swapping requires no transaction"
  (= 5 (do
         __
         @atomic-clock))

  "Any number of arguments might happen during a swap"
  (= __ (do
          (swap! atomic-clock + 1 2 3 4 5)
          @atomic-clock))

  "Atomic atoms are atomic"
  (= __ (do
          (compare-and-set! atomic-clock 100 :fin)
          @atomic-clock))

  "When your expectations are aligned with reality things, proceed that way"
  (= :fin (do
            (compare-and-set! __ __ __)
            @atomic-clock)))