clojure basics

clojure_basics.clj

;Clojure is compiled language but has a eval function like lisp which allows to run compiler within execution
;Visit https://learnxinyminutes.com/docs/clojure/ for more gists
5                      ; ⇒ 5
"hi"                   ; ⇒ "hi"
[1 2 3]                ; evaluates to the vector `[1 2 3]`
(+ 1 2)                ; evaluates to the sum of 1 and 2
(if true "yes" "no")   ; evaluates to the string "yes"
(println "hello!")     ; evaluates to nil (but also prints "hello!")


(+ 1
   (* 2 3)
   (/ 10 2))   ; ⇒ 1 + (2 * 3) + (10 / 2) = 12

(doc print)
(source print)

(def the-answer 42)

#"^foo\d?$"   ; A regular expression.
:foo          ; A keyword.

;Clojure's keywords are same as symbols in Ruby.


;Keywords are just scalars that evaluate to themselves and are useful where in other languages you might use little strings as identifiers (for example, as the keys in a hashmap).
;create a keyword from a string using the keyword method
(keyword "blues")
(type :blues) ;this is a keyword
::blues ;this is a namespace

(symbol 'foo)
(symbol :foo) ;This won't work as keywords cannot be converted to symbols in clojure

(eval :blues) ;Lisp like eval

;defs are evaluated only once whereas defns (with or without arguments) are evaluated (executed) every time
;defs cannot have any arguments
;defns should have arguments
;type returns type after evaluation
(def blue "color")
(type blue) ;will show java.lang.String
(defn add [a b] (+ a b))
(type add) ;user$add

(type 'tilak')
;clojure.lang.Symbol

(type "tilak")
;java.lang.String

;if statement with if and else branch
(if true "tilak" "patidar")

;do lets you to use multiple lines in if and else branch
(if true
   (do (+ 5 2))
   (do (-5 2))
   )

;when is like if but no else branch
(when true (println "tilak"))

(nil? 1)
;false

(nil? nil)
;true

(= 1 1)
;just single = is a equality operator for any kind of clojure object data type

(or true false)
(and true false)

;clojure does not have assignments with = instead use def to define variable names
(def my-name "tilak")

;clojure does not concat strings with + use str instead
(str "tilak" " " "patidar")

(def a [1,2,3])
(get a 2)
(contains? a 2)

(+ 1 2 3 4)
(* 1 2 3 4)
(first [1 2 3 4])
(last [1 2 3 4])

#{12 3 5} ;hash set
(hash-set 1 2 3); or another way of making a hash set

(inc 1.1)
(map inc [1 2 3])

;number of arguments a function has is it's arity
(defn sum 
   "Adds two numbers" 
   [a b]
  (+ a,b)
)

;functions having multiple arity
(defn sum
   ([a b]
    (println "two args")
    (+ a b)
    )
   ([a b c]
    (println "three args")
    (+ a b c)
      )
)

;anonyoumous functions
(fn [a] (* a 3))
((fn [a] (* a 3)) 8) ;24

;; Function call
(* 8 3)
;; Anonymous function
#(* % 3)

;multiple arguments in anonyoumous function
(#(str %1 " and " %2) "cornbread" "butter beans")

(defn pos-neg-or-zero
  "Determines whether or not n is positive, negative, or zero"
  [n]
  (cond
    (< n 0) "negative"
    (> n 0) "positive"
    :else "zero"))