andymatuschak

A composable pattern for pure state machines with effects

State machines are everywhere in interactive systems, but they're rarely defined clearly and explicitly. Given some big blob of code including implicit state machines, which transitions are possible and under what conditions? What effects take place on what transitions?

There are existing design patterns for state machines, but all the patterns I've seen complect side effects with the structure of the state machine itself. Instances of these patterns are difficult to test without mocking, and they end up with more dependencies. Worse, the classic patterns compose poorly: hierarchical state machines are typically not straightforward extensions. The functional programming world has solutions, but they don't transpose neatly enough to be broadly usable in mainstream languages.

Here I present a composable pattern for pure state machiness with effects,

djspiewak

Explaining Miles's Magic

Miles Sabin recently opened a pull request fixing the infamous SI-2712. First off, this is remarkable and, if merged, will make everyone's life enormously easier. This is a bug that a lot of people hit often without even realizing it, and they just assume that either they did something wrong or the compiler is broken in some weird way. It is especially common for users of scalaz or cats.

But that's not what I wanted to write about. What I want to write about is the exact semantics of Miles's fix, because it does impose some very specific assumptions about the way that type constructors work, and understanding those assumptions is the key to getting the most of it his fix.

For starters, here is the sort of thing that SI-2712 affects:

def foo[F[_], A](fa: F[A]): String = fa.toString

lenguyenthanh

Small gist shows how to config Dagger 2 to an Android project

vasanthk

System Design Cheatsheet

Picking the right architecture = Picking the right battles + Managing trade-offs

Basic Steps

1. Clarify and agree on the scope of the system

• User cases (description of sequences of events that, taken together, lead to a system doing something useful)
  • Who is going to use it?
  • How are they going to use it?

mttkay

public class Pager<I, O> {

    private static final Observable FINISH_SEQUENCE = Observable.never();

    private PublishSubject<Observable<I>> pages;
    private Observable<I> nextPage = finish();
    private Subscription subscription = Subscriptions.empty();

    private final PagingFunction<I> pagingFunction;
    private final Func1<I, O> pageTransformer;

lenguyenthanh

public class RootUtil {
    public static boolean isDeviceRooted() {
        return checkRootMethod1() || checkRootMethod2() || checkRootMethod3();
    }

    private static boolean checkRootMethod1() {
        String buildTags = android.os.Build.TAGS;
        return buildTags != null && buildTags.contains("test-keys");
    }

bpierre

Switch To Vim For Good

NOTE: This guide has moved to https://github.com/bpierre/switch-to-vim-for-good

This guide is coming from an email I used to send to newcomers to Vim. It is not intended to be a complete guide, it is about how I switched myself.

My decision to switch to Vim has been made a long time ago. Coming from TextMate 1, I wanted to learn an editor that is Open Source (so I don’t lose my time learning a tool that can be killed), cross platform (so I can use it everywhere), and powerful enough (so I won’t regret TextMate). For these reasons, Vim has always been the editor I wanted to learn, but it took me several years before I did it in a way that works for me. I tried to switch progressively, using the Janus Vim distribution for a few months, then got back to using TextMate 2 for a time, waiting for the next attempt… here is what finally worked for me.

Original gist with comments: https://gist.github.com/bpierre/0a0025d348b6001394e0

chrisbanes

/*
 * Copyright 2014 Chris Banes
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software

staltz

The introduction to Reactive Programming you've been missing

(by @andrestaltz)

---

This tutorial as a series of videos

If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.

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Kartones

PSQL

Magic words:

psql -U postgres

Some interesting flags (to see all, use -h or --help depending on your psql version):

• -E: will describe the underlaying queries of the \ commands (cool for learning!)
• -l: psql will list all databases and then exit (useful if the user you connect with doesn't has a default database, like at AWS RDS)