Clojure introduction

intro.clj

; Why Clojure?
;
; * Interactive
; * Succinct
; * Consistent
; * Java interoperability

; Try Clojure is an online "repl", where you can try out Clojure expressions.
; http://tryclj.com/

; Simple values are echoed back from the repl.
1
;> 1

[1 2 3]
;> [1 2 3]

; Wrapping an expression in ()s causes a function to be invoked.
(+ 1 2)
;> 3
  
; The function is always comes in first position.
(- 2 1)
;> 1

(* 3 4)
;> 12

(* 3 (+ 2 2))
;> 12

; Exercise - try out some arithmetical expressions.
; Exercise - what does (doc +) do?

; We can define our own values.
(def age 99)
;> #'sandbox15110/age

age
;> 99

; Exercise - define pi.

; We can define our own functions.
(def plus-one (def [x] (+ x 1))
;> #'sandbox15110/plus-one

plus-one
;> #'sandbox15110/plus-one

(plus-one 2)
;> 3

; Exercise - define your own minus-one function.
; Exercise - define your own area function.
; Exercise - extract square into its own function.

; We can write out lists.
[1 2 3]
;> [1 2 3]

; There are library functions that work on lists.
(first [1 2 3])
;> 1

(take 2 [1 2 3])
;> [1 2]

(drop 1 [1 2 3])
;> [2 3]

; Exercise - define an xth function that returns the xth element of a list.
;             (xth 0 [1 2 3]) should return the same as (first [1 2 3])
;
; Hint: you can write it in terms of first and drop.           

; Some functions return boolean values.
(= 3 4)
;> false

(< 2 3)
;> true

; We can use if to branch.
(if (= 4 5) "goodbye" "hello")
;> "hello"

(if (> 3 2) "goodbye" "hello")
;> "goodbye"

; Exercise - write a maximum function, the greater of its two arguments.
; Exercise - write an absolute function, that returns 3 if given 3, and 4 if given -4.