marshall-lee

sqrti x = (truncate . sqrt . fromInteger) x
primes = filter (\n -> all (\y -> n `mod` y /= 0) [2..sqrti(n)]) [2..]
isPrime x = elem x (takeWhile (<= x) primes)
 
-- ghci> take 10 primes
-- [2,3,5,7,11,13,17,19,23,29]
-- ghci> take 8 (drop 2 primes)
-- [5,7,11,13,17,19,23,29]
-- ghci> take 100500 primes
-- ...

marshall-lee

require 'benchmark'
 
# returns lazy enumerator
def primes_lazy_but_stupid
  (2..Float::INFINITY).lazy.reject{ |i| (2..Math.sqrt(i)).any?{ |j| i % j == 0 } }
end
 
# returns just array of primes <= n
def primes_just_stupid(n)
  (2..n).reject{ |i| (2..Math.sqrt(i)).any?{ |j| i % j == 0 } }

marshall-lee

-module(sleep_sort).

-export([sort/1, sort_better/1]).

sort(List) ->
    Self = self(),
    lists:foreach(fun(X) -> spawn(fun() -> timer:sleep(X), Self ! X end) end, List),
    [receive X -> X end || _ <- lists:seq(1, length(List))].

sort_better(List) ->

marshall-lee

PromiseSort = {
    pivotIndexMedian: function (ary, pred, startIndex, endIndex) {
        var midIndex = Math.floor((startIndex + endIndex) / 2),
            indexes = [startIndex, midIndex, endIndex];
        return indexes.sort(function (i, j) {
            return pred(ary[i], ary[j]);
        })[1]; // return median index
    },
    pivotIndexRandom: function (_ary, _pred, startIndex, endIndex) {
        return Math.floor(Math.random() * (endIndex - startIndex + 1)) + startIndex;

marshall-lee

# this is a rewriter class for adding `null: true` to timestamps migrations when upgrading to Rails 4.2 or higher.
# calling `timestamps` without specifying `null: false|true` is now deprecated, so it must be fixed in all of your db migrations
# 
# script uses this approach: http://whitequark.org/blog/2013/04/26/lets-play-with-ruby-code/
# to run:
# gem install parser
# ruby-rewrite -l timestamps_fix.rb -m ~/code/my_rails_app/db/migrate
# (c) Vladimir Kochnev 2014

class TimestampsFix < Parser::Rewriter

marshall-lee

str = "abc"
1000.times do
  action = [:upcase, :downcase, :reverse].sample
  str = str.send action
end
puts str

# What is the probability that "CBA" will be output?
# Какова вероятность, что будет выведена строка "CBA"?

marshall-lee

# put this to lib/capistrano/tasks/leye.rake
namespace :leye do
  desc "Show leye information"
  task :info do
    on roles(:app) do
      within current_path do
        with fetch(:leye_env) do
          if execute :leye, 'load'
            puts capture(:leye, 'info')
          end

marshall-lee

# Online (non-blocking) ActiveRecord migrations using pt-online-schema-change utility from Percona Toolkit.
#
# In your Rails app put it as lib/online_change_table.rb
# Now you can use it in your migration file:
#
#    require 'online_change_table'
#
#    class AddSomethingToSomethings < ActiveRecord::Migration
#      def up
#        online_change_table :somethings do |t|

marshall-lee

#!/usr/bin/env ruby

require 'open-uri'

url = ARGV[0]
$stderr.puts 'URL not specified' and exit 1 unless url
uri = URI.parse url
$stderr.puts 'This should be 9gag.com URL' and exit 1 if uri.host != '9gag.com'
m = uri.path.match %r{^/gag/(\w+)$}
$stderr.puts 'Malformed URL!' and exit 1 unless m

marshall-lee

h = { [] => :ok }
p h[[]] # ok

h = { [:lol] => :ok }
p h[[:lol]] # ok

h = { [] => :ok }
h.first.first << :lol

p h[[:lol]] # nil