Tutorial by Examples: r

Normal forms

This example provides a brief overview - for a more in-depth explanation of normal forms and examples, see this question. Reduced normal form The reduced normal form (or just normal form, when the context is clear) of an expression is the result of evaluating all reducible subexpressions in the gi...

Haskell Language • Strictness

Using rewrite rules on overloaded functions

In this question, @Viclib asked about using rewrite rules to exploit typeclass laws to eliminate some overloaded function calls: Mind the following class: class ListIsomorphic l where toList :: l a -> [a] fromList :: [a] -> l a I also demand that toList . fromList == id. H...

Haskell Language • Rewrite rules (GHC)

What is Entity Framework ?

Writing and managing ADO.Net code for data access is a tedious and monotonous job. Microsoft has provided an O/RM framework called "Entity Framework" to automate database related activities for your application. Entity framework is an Object/Relational Mapping (O/RM) framework. It is an e...

Entity Framework • Getting started with Entity Framework

Reverse

Inverts the order of the elements in a sequence. If there is no items throws a ArgumentNullException: source is null. Example: // Create an array. int[] array = { 1, 2, 3, 4 }; //Output: // Call reverse extension method on the array. //4 var reverse = array.R...

C# Language • LINQ Queries

Enumerating the Enumerable

The IEnumerable<T> interface is the base interface for all generic enumerators and is a quintessential part of understanding LINQ. At its core, it represents the sequence. This underlying interface is inherited by all of the generic collections, such as Collection<T>, Array, List<T&g...

C# Language • LINQ Queries

Creating a Seeder

To create seeders, you may use the make:seeder Artisan command. All seeders generated will be placed in the database/seeds directory. $ php artisan make:seeder MoviesTableSeeder Generated seeders will contain one method: run. You may insert data into your database in this method. <?php us...

Laravel • Seeding

Existential Operator

CoffeeScript's existential operator ? check if the variable is null or undefined. 1. Check for null or undefined. alert "Hello CoffeeScript!" if myVar? javascript equivalent: if (typeof myVar !== "undefined" && myVar !== null) { alert("Hello CoffeeScript!&qu...

coffeescript • Operators

Partially update the view

Makes an ajax request and updates only part of the view. Bean.java @ManagedBean @ViewScoped public class Bean { public Date getCurrentDate() { return new Date(); } } sample.xhtml <html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="http://xmlns...

jsf • Ajax Integration

Send form parts and listen to the request

Makes a request only sending part of the form. The text1 value is set, but not text2, as the listener states. Bean.java @ManagedBean @ViewScoped public class Bean { private String text1; private String text2; public String getText1() { return text1; } pu...

jsf • Ajax Integration

Ajax on javascript event

The date is updated whenever user types on the input field: Bean.java @ManagedBean @ViewScoped public class Bean { public Date getCurrentDate(){ return new Date(); } } sample.xhtml <html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="http://x...

jsf • Ajax Integration

Switch to a frame using C#

1. Switch to a frame by Index. Here we are switching to index 1. Index refers to the order of frames on the page. This should be used as a last resort, as frame id or names are much more reliable. driver.SwitchTo().Frame(1); 2. Switch to a frame by Name driver.SwitchTo().Frame("Name_Of_Fr...

selenium-webdriver • Switching Frames

Automatically processing data received from a serial port

Some devices connected through a serial port send data to your program at a constant rate (streaming data) or send data at unpredictable intervals. You can configure the serial port to execute a function automatically to handle data whenever it arrives. This is called the "callback function&quo...

MATLAB Language • Using serial ports

Local Type Inference

Scala has a powerful type-inference mechanism built-in to the language. This mechanism is termed as 'Local Type Inference': val i = 1 + 2 // the type of i is Int val s = "I am a String" // the type of s is String def squared(x : Int) = x*x // the return type ...

Scala Language • Type Inference

Type Inference And Generics

The Scala compiler can also deduce type parameters when polymorphic methods are called, or when generic classes are instantiated: case class InferedPair[A, B](a: A, b: B) val pairFirstInst = InferedPair("Husband", "Wife") //type is InferedPair[String, String] // Equiv...

Scala Language • Type Inference

Limitations to Inference

There are scenarios in which Scala type-inference does not work. For instance, the compiler cannot infer the type of method parameters: def add(a, b) = a + b // Does not compile def add(a: Int, b: Int) = a + b // Compiles def add(a: Int, b: Int): Int = a + b // Equivalent expression, compiles ...

Scala Language • Type Inference

Splitting a string into a list

To split strings, Guava introduces the Splitter class. Why not use Java's splitting capabilities? As a rule, Guava does not duplicate functionality that is readily available in Java. Why then do we need an additional Splitter class? Do the split methods in Java's String class not provide us with a...

guava • Strings

Basics: initialize the SPI and a chip select pin, and perform a 1-byte transfer

#include <SPI.h> #define CSPIN 1 void setup() { pinMode(CSPIN, OUTPUT); // init chip select pin as an output digitalWrite(CSPIN, 1); // most slaves interpret a high level on CS as "deasserted" SPI.begin(); SPI.beginTransaction(SPISettings(1000000, MSBFIRST, SPI_MO...

arduino • SPI Communication

Moving the servo back and forth

#include <Servo.h> Servo srv; void setup() { srv.attach(9); // Attach to the servo on pin 9 } To use a servo, you need to call attach() function first. It starts generating a PWM signal controlling a servo on a specified pin. On boards other than Arduino Mega, use of Servo lib...

arduino • Servo

length([String])

Returns the number of characters of the given String Considerations If a number is given instead a String, the result will be the length of the String representing the given number. I.e. If we execute length(12345) the result will be the same as length("12345"), that is 5 If...

awk • Built-in functions

Adding custom filters/functions

Here are some example on how to add new filters/functions to twig,the synax for adding Twig_Functions are the same as the Twig_Filter ones, just change the keywords accordingly <?php $twig = new Twig_Environment($loader); /* You can chain a global function */ $twig->addFilter(ne...

twig • Extending twig