number23

user=> (type [])
clojure.lang.PersistentVector
user=> (type '())
clojure.lang.PersistentList$EmptyList
user=> (type [1])
clojure.lang.PersistentVector
user=> (type '(1))
clojure.lang.PersistentList
user=> (= [] '())
true

number23

(defn prime? [n]
  (cond
   (== 1 n) false
   (== 2 n) true
   (even? n) false
   :else (->> (range 3 (inc (Math/sqrt n)) 2)
              (filter #(zero? (rem n %))) empty?)))

(time (prime? 1125899906842679)) 
; "Elapsed time: 2181.014 msecs" 

number23

'x 
;= x

'(+ x x)
;= (+ x x)
 
(list? '(+ x x)) 
;= true

(list '+ 'x 'x) 

number23

Literal syntax                 Numeric type

42, 0xff, 2r111, 040           long (64-bit signed integer)
3.14, 6.0221415e23             double (64-bit IEEE floating point decimal)
42N                            clojure.lang.BigInt (arbitrary-precision integera)
0.01M                          java.math.BigDecimal (arbitrary-precision signed floating point decimal)
22/7                           clojure.lang.Ratio

number23

user=> (try (/ 1 0) true (catch Exception e false))
false
user=> (try (/ 1 1) true (catch Exception e false))
true

number23

Shell:~ >: cat t.clj
(ns t)

(defn -main [& args]
  (println "Hello world"))
Shell:~ >: java -cp ".:.clojure/clojure.jar" clojure.main -m t
Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF-8
Hello world
Shell:~ >: 

number23

(use '[clojure.inspector :only (inspect inspect-tree)])
(inspect-tree (System/getProperties))
(inspect-tree {:clojure {:creator "Rich" :runs-on-jvm true}})

number23

user=> (for [file "ABCDEFGH" rank (range 1 9)] (format "%c%d" file rank))
("A1" "A2" "A3" "A4" "A5" "A6" "A7" "A8" "B1" "B2" "B3" "B4" "B5" "B6" "B7" "B8" "C1" "C2" "C3" "C4" "C5" "C6" "C7" "C8" "D1" "D2" "D3" "D4" "D5" "D6" "D7" "D8" "E1" "E2" "E3" "E4" "E5" "E6" "E7" "E8" "F1" "F2" "F3" "F4" "F5" "F6" "F7" "F8" "G1" "G2" "G3" "G4" "G5" "G6" "G7" "G8" "H1" "H2" "H3" "H4" "H5" "H6" "H7" "H8")
user=> (for [rank (range 1 9) file "ABCDEFGH"] (format "%c%d" file rank))
("A1" "B1" "C1" "D1" "E1" "F1" "G1" "H1" "A2" "B2" "C2" "D2" "E2" "F2" "G2" "H2" "A3" "B3" "C3" "D3" "E3" "F3" "G3" "H3" "A4" "B4" "C4" "D4" "E4" "F4" "G4" "H4" "A5" "B5" "C5" "D5" "E5" "F5" "G5" "H5" "A6" "B6" "C6" "D6" "E6" "F6" "G6" "H6" "A7" "B7" "C7" "D7" "E7" "F7" "G7" "H7" "A8" "B8" "C8" "D8" "E8" "F8" "G8" "H8")


from: http://stackoverflow.com/questions/10966142/what-is-the-difference-between-while-and-when-in-clojure
 
:when iterates over the bindings, but only evaluates the body of the loop when the condition is true. 
:while iterates ov

number23

(declare my-odd? my-even?)

(defn my-odd? [n]
  (if (= n 0)
    false
    #(my-even? (dec n))))

(defn my-even? [n]
  (if (= n 0)
    true

number23

#!/bin/sh

echo "SYSTEM Backup start at `date`!"

cd /
tar -czpf - --exclude=/proc \
        --exclude=/sys \
        --exclude=/mnt \
        --exclude=/media \
        --exclude=/dev \