A Taste of Clojure
Now that we have a REPL session, let's explore some core concepts in Clojure- expressions, vars, functions and collections.
Expressions
Calculate 1.4 * 67 :
(* 1.4 67)
Output
Print "Hello, world!":
(println "Hello, world!")
Output
Sort a Vector (Array) of Numbers:
(sort [4.2 10 1 4.5 1 15])
Output
Sum a Vector of Numbers:
(reduce + [4.2 10 1 4.5 1 15])
Output
Increment a Vector of Numbers:
(map inc [4.2 10 1 4.5 1 15])
Output
Variables
Using Variables (a.k.a. "vars")
Define a "var" with string content:
(def my-string-var "Hello, world")
Display the value of the var:
my-string-var
Display the length of the string
(count my-string-var)
Output
Functions
Defining Functions
Define a function that takes two integer arguments, x and y, and returns the product x * y:
(defn my-mult [x y] (* x y))
Invoke the function to multiply two numbers:
(my-mult 10 50)
Output
Collections
Vectors
Define a var that contains a vector of keywords representing states:
(def valid-states [:stopped :stopping :running])
Add elements to the vector:
(conj valid-states :starting :paused)
Return the third element of the vector:
(get valid-states 2)
Output
Maps
Define a var that contains a map which maps states to strings suitable for display in a UI:
(def state-display-vals {:stopped "Stopped" :stopping "Stopping" :running "Running"})
Get the display value for the :stopped state:
(:stopped state-display-vals)
Added a mapping for the :starting state:
(assoc state-display-vals :starting "Starting")
Output
Sets
Define a var that contains a set of keywords for the days of the week:
(def my-set #{:Mon :Tue :Wed :Thu :Fri :Sat :Sun})
Check set membership:
(contains? days-of-week :Sun)
(contains? days-of-week :Fun)
Return a member if it exists, otherwise return nil:
(days-of-week :Sun)
(days-of-week :Fun)
Output
Lists
Define a var that contains a list of days of the week:
(def my-list '(:Mon :Tue :Wed :Thu :Fri :Sat :Sun))
Get the first element in the list:
(first my-list)
Return a new list consisting of all elements in the list except the first:
(rest my-list)
Return a new list consisting of all elements in the list with a new element prepended:
(conj my-list :Fun)
Output
