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A before-and-after guide to Ruby's Enumerable module

Basics

each

Ruby's for keyword is an anti pattern! In fact, it's actually slower than each and uses each in the background.

Before

for n in [1, 2, 3, 4]
 puts n

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package main

import(
  "bufio"
  "fmt"
  "log"
  "os"
  "regexp"
)

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mapSum :: Num a => (a -> a) -> [a] -> a
mapSum f xs = sum $ map f xs

nestedSum :: Num a => [a] -> [a] -> (a -> a -> a) -> a
nestedSum xs ys f = mapSum (\ x -> mapSum (f x) ys) xs

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package main

import (
  "os"
  "fmt"
)

func main() {
  for _, pair := range os.Environ() {
    fmt.Println(pair)

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Go benchmark: Various methods of loading maps

This benchmark was used for run.

Running

go test -bench=.

Note that there are no dependencies besides Go itself.

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# usage: ruby web_cat.rb URL
require 'nokogiri'
require 'open-uri'

uri = ARGV[0]
doc = Nokogiri::HTML open uri
puts doc.text

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require 'open-uri'

changelog = open 'https://raw.githubusercontent.com/angular/angular.js/master/CHANGELOG.md'
headlines = changelog.grep(/^# /)

headlines.each do |headline|
  version, codename = headline.match(/(\S+) +(\S+) +\([\d-]+\)/).captures
  puts "#{version}: #{codename}"
end

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-- | lookup' @key assocs@ looks up a value in an association list. While lookup
-- finds a tuple where the first value matches and returns the second, lookup'
-- does the opposite.
lookup' :: (Eq b) => b -> [(a,b)] -> Maybe a
lookup' _ [] =  Nothing
lookup' key ((x,y):xys)
  | key == y  =  Just x
  | otherwise =  lookup' key xys

-- Prints "Just 2".

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main = getContents >>= putStr

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#!/bin/bash
# Sometimes when you use AirPlay, your Mac's audio may die.
# If so, you can run this script to restart coreaudiod, which should fix your problem.
# Note that this may be slightly interactive because it uses sudo.

sudo killall coreaudiod