Clojure 101

clojure101.clj

;; Add dependencies live on lein repl
;; ------------------------------

; in project.clj, add to dependencies vector: [com.cemerick/pomegranate "0.3.0"]
[com.cemerick/pomegranate "0.3.1"]

; example adding deps via repl 
(cemerick.pomegranate/add-dependencies
 :coordinates '[[midje "1.8.2"]]
 :repositories (merge cemerick.pomegranate.aether/maven-central 
                       {"clojars" "http://clojars.org/repo"}))



;; Stuart Sierra's System: 
;; ------------------------------

; reloaded.repl is best practice workflow working with System.
; It provides small function which working around 2 var: system and initializer

(set-init! init-fn) ;; alter initializer to init-fn in first arg 
(init) ;; call component/stop if system not nil then call (init) saved to system
(start) ;; save system with result of component/start 
(stop) ;; save system with result of component/stop 
(go) ;; call (init) followed by (start) 
(clear) ;; stop the system and save nil to system
(reset) ;; call (clear) followed by (clojure.tools.namespace.repl/refresh :after go)


;; Using clj-wallhack to access privates
;; ------------------------------

(wall.hack/field org.httpkit.BytesInputStream :buf __obj)  ;; => byte-array

; Note: In cider, inspect on object instance will reveals all its fields, 
; whereas inspecting on class will show all public methods.


;; Runtime reflection / meta programming
;; ------------------------------

; Symbol:  'parse, `parse
; Var:  #'parse, (var parse), (resolve 'parse)

; `resolve` run on runtime whereas `var` is used during compilation, e.g. #'parse is expanded as (var parse)

; Clojure call function via its string: 
(-> "+" symbol resolve deref (apply (range 10)))


;; Evaluating protocol will result a map which contains useful information of the protocol itself. 
;; ------------------------------


;; Find out symbols defined in an ns
;; ------------------------------

(-> 'cemerick.pomegranate find-ns ns-publics keys)