hellerbarde

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

adamwiggins

Make it real

Ideas are cheap. Make a prototype, sketch a CLI session, draw a wireframe. Discuss around concrete examples, not hand-waving abstractions. Don't say you did something, provide a URL that proves it.

Ship it

Nothing is real until it's being used by a real user. This doesn't mean you make a prototype in the morning and blog about it in the evening. It means you find one person you believe your product will help and try to get them to use it.

Do it with style

rylev

## Sort Algorithms in Elixir

# Selection Sort

defmodule Selection do
  def sort(list) when is_list(list) do
    do_selection(list, [])
  end

  def do_selection([head|[]], acc) do

gtallen1187

"A little bit of slope makes up for a lot of y-intercept"

01/13/2012. From a lecture by Professor John Ousterhout at Stanford, class CS140

Here's today's thought for the weekend. A little bit of slope makes up for a lot of Y-intercept.

[Laughter]

AtulKsol

psql: FATAL: Peer authentication failed for user “postgres” (or any user)

The connection failed because by default psql connects over UNIX sockets using peer authentication, that requires the current UNIX user to have the same user name as psql. So you will have to create the UNIX user postgres and then login as postgres or use sudo -u postgres psql database-name for accessing the database (and psql should not ask for a password).

If you cannot or do not want to create the UNIX user, like if you just want to connect to your database for ad hoc queries, forcing a socket connection using psql --host=localhost --dbname=database-name --username=postgres (as pointed out by @meyerson answer) will solve your immediate problem.

But if you intend to force password authentication over Unix sockets instead of the peer method, try changing the following pg_hba.conf* line:

from

cheerfulstoic

After reading Why I'm Frequently Absent from Open Source by James Long and listening the corresponding The Changelog episode, I dwelt on the idea and believe that open source maintainers...

• ... should never be ashamed if they don't have time for a project.
• ... should be honest with themselves and open with their users so that everybody can be on the same page
• ... are people and they have at one time or another responsibilities or hardships that they need to attend to which reasonably take them away from a project
• ... may also reasonbly decide that they don't like the direction of a project or that they would like to explore other things and may leave a project permanently.

Along this line of thinking I've created a set of descriptions for different levels at which a project might be maintained. A maintainer can use these to announce to their users the current ability that they have to dedicate to a pr

VictorTaelin

async/await is just the do-notation of the Promise monad

CertSimple just wrote a blog post arguing ES2017's async/await was the best thing to happen with JavaScript. I wholeheartedly agree.

In short, one of the (few?) good things about JavaScript used to be how well it handled asynchronous requests. This was mostly thanks to its Scheme-inherited implementation of functions and closures. That, though, was also one of its worst faults, because it led to the "callback hell", an seemingly unavoidable pattern that made highly asynchronous JS code almost unreadable. Many solutions attempted to solve that, but most failed. Promises almost did it, but failed too. Finally, async/await is here and, combined with Promises, it solves the problem for good. On this post, I'll explain why that is the case and trace a link between promises, async/await, the do-notation and monads.

First, let's illustrate the 3 styles by implementing

cscalfani

How to think about Monads

UPDATE 2021: I wrote this long before I wrote my book Functional Programming Made Easier: A Step-by-step Guide. For a much more in depth discussion on Monads see Chapter 18.

Initially, Monads are the biggest, scariest thing about Functional Programming and especially Haskell. I've used monads for quite some time now, but I didn't have a very good model for what they really are. I read Philip Wadler's paper Monads for functional programming and I still didnt quite see the pattern.

It wasn't until I read the blog post You Could Have Invented Monads! (And Maybe You Already Have.) that I started to see things more clearly.

This is a distillation of those works and most likely an oversimplification in an attempt to make things easier to understand. Nuance can come later. What we need when first le

abiodun0

const zero = () => false;
const isZero = (a) => a == zero();

const succ = (a) => () => a;
const pred = (a) => a();

const converToPeano = (n, acc = zero()) => n === 0 ? acc : converToPeano(n - 1, succ(acc))

const _0 = zero(),
      _1 = succ(_0),

rylev

Learning Rust

The following is a list of resources for learning Rust as well as tips and tricks for learning the language faster.

Warning

Rust is not C or C++ so the way your accustomed to do things in those languages might not work in Rust. The best way to learn Rust is to embrace its best practices and see where that takes you.

The generally recommended path is to start by reading the books, and doing small coding exercises until the rules around borrow checking become intuitive. Once this happens, then you can expand to more real world projects. If you find yourself struggling hard with the borrow checker, seek help. It very well could be that you're trying to solve your problem in a way that goes against how Rust wants you to work.