Clojure notes

clojure_notes.md

Nuggets of Clojure

Data Structures

Core data structures are immutable

• Numbers

  43
  6.7

• Strings

  • only double quotes
  • no string interpolation; concat using str

  (println "Lord Voldemort")
  (println "\"He who must not be named\"")
  (println "\"Great cow of Moscow!\" - Hermes Conrad")

• Maps

  • like dictionaries or hashes in other languages

  {:a 3 :b 4 :c 18 }

  • lookup

  (get {:a 3 :b 4 :c 18 } :b )
  ; => 4
  
  (:b {:a 3 :b 4 :c 18 })
  ; => 4
  
  (get mymap {:a 3 :b 4 :c 18 } )
  (:b mymap)
  ; => 4

• Keywords

  • primarily used as keys in maps

  :a
  :spongebob
  :andy

• Vectors

  • similar to an array in that it's a 0-indexed collection

  [3 2 1]
  
  (get [3 2 1] 0)
  ; => 3
  
  ;; Another example of getting by index. Notice as well that vector
  ;; elements can be of any type and you can mix types.
  (get ["a" {:name "Andrew Vida"} "c"] 1)
  ; => {:name "Andrew Vida"}

• Lists

  • similar to vectors in that they're linear collections of values. You can't access their elements in the same way, though:

  ;; Notice the leading single quote
  '(1 2 3 4)
  
  ;; Doesn't work for lists
  (get '(100 200 300 400) 0)
  ;; This does
  (nth `(100 200 300 400) 3)
  ; => 400
  

• Sets

  • Unique sets of values

  #{"Andy" "Jennifer" 3 }
  
  (get #{"Andy" "Jennifer" 3 } 3 )
  ; => 3
  
  ;; If you try to add "Andy" to a set which already contains "Andy",
  ;; the set still only has one "Andy"
  (conj #{"Andy" "Jennifer" 3 } "Andy" )
  ; => #{"Andy" "Jennifer" 3 }
  
  (get #{"Andy" "Jennifer" 3 } :a )
  ; => nil
  

• Symbols

  • Identifiers that are normally used to refer to something. Let's associate a value with a symbol:

  ;; my-family is a symbol
  (def my-family
    [ "me"
      "wife"
      "kids"])