tiensonqin

(def v [[1 2] [1 1] [2 1] [2 4]])

(partition-by #(first %) v)
;; => (([1 2] [1 1]) ([2 1] [2 4]))

(group-by #(first %) v)
;; => {1 [[1 2] [1 1]], 2 [[2 1] [2 4]]}

;; ruby version
;; v.group_by{|v| v[0]}

tiensonqin

--langdef=Clojure
--langmap=Clojure:.clj
--regex-clojure=/\([ \t]*create-ns[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/n,namespace/
--regex-clojure=/\([ \t]*def[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/d,definition/
--regex-clojure=/\([ \t]*defn[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/f,function/
--regex-clojure=/\([ \t]*defn-[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/p,private function/
--regex-clojure=/\([ \t]*defmacro[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/m,macro/
--regex-clojure=/\([ \t]*definline[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/i,inline/
--regex-clojure=/\([ \t]*defmulti[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/a,multimethod definition/
--regex-clojure=/\([ \t]*defmethod[ \t]+([-[:alnum:]*+!_:\/.?]+)/\1/b,multimethod instance/

tiensonqin

My efforts to port http://www.youtube.com/watch?v=f6kdp27TYZs to Clojure.

A boring function (6:22)

func boring(msg string) {
  for i := 0; ; i++ {
    fmt.Println(msg, i)
    time.Sleep(time.Second)
 }

tiensonqin

FallVelocity = fun(Distance) ->
                       math:sqrt(2 * 9.8 * distance)
               end.

(defn fall-velocity
  [distance]
  (sqrt (* 2 9.8 distance))

tiensonqin

;; Clojure vs Erlang on counter recursion

;; Clojure version
(ns count)

(defn down
  [x]
  (if (zero? x) (prn "blastoff!")
      (do
        (prn x)

tiensonqin

-module(pascal).
-export([triangle/1]).

triangle(Rows) ->
  triangle([[0,1,0]],1,Rows).

triangle(List, Count, Rows) when Count >= Rows -> lists:reverse(List);

triangle(List, Count, Rows) ->
  [Previous | _] = List,

tiensonqin

%% erlang pattern matching and list comprehension vs clojure destructure and hof
-module(shop).
-export([total/1]).

cost(oranges) -> 5;
cost(newspaper) -> 8;
cost(apples) -> 2;
cost(pears) -> 9;
cost(milk) -> 7.

tiensonqin

(ns example.errors)

(defn clean-address [params]
  "Ensure (params :address) is present"
  (if (empty? (params :address))
    [nil "Please enter your address"]
    [params nil]))

(defn clean-email [params]
  "Ensure (params :email) matches *@*.*"

tiensonqin

-module(math).
-compile(export_all).

%% erlang version
pow(_X, 0) ->
  1;
pow(X, N) ->
  X * pow(X, N-1).

%% clojure version

tiensonqin

%% clojure version, recursion is all you need
(defn take
 "Returns a lazy sequence of the first n items in coll, or all items if
  there are fewer than n."
  {:added "1.0"
   :static true}
 [n coll]
   (lazy-seq
           (when (pos? n)
                 (when-let [s (seq coll)]