jwhiteman

sudo apt-get update
sudo apt-get install vim

# generate keys and copy them over
ssh-copy-id -i id_rsa.pub vagrant@hnclient # move node ssh key to the client
# update /etc/hosts on each node to know at least the master; the master about the slave nodes
# make sure master can ssh into localost
cat .ssh/id_rsa.pub >> .ssh/authorized_keys

# re-read: http://stackoverflow.com/questions/8872807/hadoop-datanodes-cannot-find-namenode

jwhiteman

require 'httparty'
include HTTParty

('aa'..'zz').select { |r| 
  sleep 0.20
  puts "trying #{r}"
  self.class.head("https://twitter.com/#{r}").code == 404
}

# => ['me', 'oh']

jwhiteman

Gotcha with Erlang

➜  v-kserl-v-02-code  erl
Erlang R16B03-1 (erts-5.10.4) [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Eshell V5.10.4  (abort with ^G)
1> VALUE = fun() -> io:format("I have value!~n") end.
#Fun<erl_eval.20.80484245>
2> K = mykey.
mykey

jwhiteman

Y = fun(C) ->
  (fun(H) ->
     H(H)
   end)(
     fun(F) ->
       C(fun(X) -> (F(F))(X) end)
     end
   )
end.

jwhiteman

(define y2
  (lambda (c)
    ((lambda (h)
       (h h))
     (lambda (f)
       (c (lambda (x y)
            ((f f) x y)))))))

(define make-rember
  (y2 (lambda (f)

jwhiteman

def daemonize_app
  if RUBY_VERSION < "1.9"
    exit if fork     # jettison the terminal
    Process.setsid   # establish a new group & session leader (can only be done as a child process)
    exit if fork     # jettison the group leader. now it can't be interrupted from another group or session going down.
    Dir.chdir "/"    # change dir to root to make sure that the dir won't go away during the process run

    # as a demon we won't be needing these...
    STDIN.reopen  "/dev/null"
    STDOUT.reopen "/dev/null", 'a'

jwhiteman

defmodule MyList do

  # version 1: continuation passing style
  def flatten(l), do: flatten(l, fn (result) -> result end)
  def flatten([], col), do: col.([])
  def flatten([h|t], col) when not is_list(h) do
    flatten(t, fn (acc) -> col.([h | acc]) end)
  end
  def flatten([h|t], col) do
    col.(

jwhiteman

% Andrea Leopardi's list parser
% http://andrealeopardi.com/posts/tokenizing-and-parsing-in-elixir-using-leex-and-yecc/
Nonterminals list elems elem.
Terminals '[' ']' ',' int atom.

Rootsymbol list.

list ->
  '[' ']' : [].
list ->

jwhiteman

defmodule Ring do
  def node(name, next_pid) do
    receive do
      1 -> 
        send next_pid, 1
      n when is_number(n) ->
        send next_pid, n
        node(name, next_pid)
    end
  end

jwhiteman

;; letrec practice
;; fold
;; map
;; filter
;; mapcat

(define (fold fold-f acc l)
  (letrec
      ((FOLD (lambda (acc l)
                (cond