Tutorial by Examples: r

On a very high level, Prolog only has a single data type, called term. In Prolog, all data is represented by Prolog terms. Terms are defined inductively: an atom is a term. Examples of atoms are: x, test and 'quotes and space'. a variable is a term. Variables start with an uppercase letter or un...

Consider the following block of code. try { using (var disposable = new MyDisposable()) { throw new Exception("Couldn't perform operation."); } } catch (Exception ex) { Console.WriteLine(ex.Message); } class MyDisposable : IDisposable { public vo...

6.0 Introduced in C# 6.0, the Null Conditional Operator ?. will immediately return null if the expression on its left-hand side evaluates to null, instead of throwing a NullReferenceException. If its left-hand side evaluates to a non-null value, it is treated just like a normal . operator. Note tha...

To connect to a local Wildfly server via the command line, the tool bin/jboss-cli.sh can be used: $ ./bin/jboss-cli.sh --connect [standalone@localhost:9990 /] To connect to a remote Wildfly server, use the --controller option: $ ./bin/jboss-cli.sh --connect --controller=localhost:9990 [stan...

int a; std::cout << a; // Undefined behavior! This results in undefined behavior, because a is uninitialised. It is often, incorrectly, claimed that this is because the value is "indeterminate", or "whatever value was in that memory location before". However, it is th...

The call/N family of predicates can call arbitrary Prolog goals at run time: ?- G=true, call(G). true. ?- G=(true,false), call(G). false.

In order to record audio from a user's microphone, we must first gain permission from the user to access the device: navigator.mediaDevices.getUserMedia({ audio: true }) .then(successCallback) .catch(failureCallback); On success, our successCallback will be called with a MediaStream ob...

Predicates that impede or prohibit a declarative reading of Prolog programs are extra-logical. Examples of such predicates are: !/0 (->)/2 and if-then-else (\+)/1 These predicates can only be understood procedurally, by taking into account the actual control flow of the interpreter, and a...

Optionals (also known as Maybe types) are used to represent a type whose contents may or may not be present. They are implemented in C++17 as the std::optional class. For example, an object of type std::optional<int> may contain some value of type int, or it may contain no value. Optionals ar...

BEGIN TRANSACTION INSERT INTO DeletedEmployees(EmployeeID, DateDeleted, User) (SELECT 123, GetDate(), CURRENT_USER); DELETE FROM Employees WHERE EmployeeID = 123; COMMIT TRANSACTION

local function A(name, age, hobby) print(name .. "is " .. age .. " years old and likes " .. hobby) end A("john", "eating", 23) --> prints 'john is eating years old and likes 23' -- oops, seems we got the order of the arguments wrong... -- this happ...

DCGs can be used for parsing. Best of all, the same DCG can often be used to both parse and generate lists that are being described. For example: sentence --> article, subject, verb, object. article --> [the]. subject --> [woman] | [man]. verb --> [likes] | [enjoys]. object ...

The C-API is the most powerful way to access PostgreSQL and it is surprisingly comfortable. Compilation and linking During compilation, you have to add the PostgreSQL include directory, which can be found with pg_config --includedir, to the include path. You must link with the PostgreSQL client s...

Prerequisites In order to run Elasticsearch, a Java Runtime Environment (JRE) is required on the machine. Elasticsearch requires Java 7 or higher and recommends Oracle JDK version 1.8.0_73. Install Oracle Java 8 sudo add-apt-repository -y ppa:webupd8team/java sudo apt-get update echo "or...

The Locals window provides easy access to the current value of variables and objects within the scope of the function or subroutine you are running. It is an essential tool to debugging your code and stepping through changes in order to find issues. It also allows you to explore properties you might...

Although people often say Sass as the name of this CSS-preprocessor, they often mean the SCSS-syntax. Sass uses the .sass file extension, while SCSS-Sass uses the .scss extension. They are both referred to as "Sass". Speaking generally, the SCSS-syntax is more commonly used. SCSS looks li...

Use charAt() to get a character at the specified index in the string. var string = "Hello, World!"; console.log( string.charAt(4) ); // "o" Alternatively, because strings can be treated like arrays, use the index via bracket notation. var string = "Hello, World!";...

CREATE TABLE person ( person_id BIGINT NOT NULL, last_name VARCHAR(255) NOT NULL, first_name VARCHAR(255), address VARCHAR(255), city VARCHAR(255), PRIMARY KEY (person_id) ); Alternatively, you can place the PRIMARY KEY constraint directly in the column definition: ...

OrientDB is available in two editions: Community Edition is released as an open source project under the Apache 2 license. This license allows unrestricted free usage for both open source and commercial projects. Enterprise Edition is commercial software built on top of the Community Edit...

In ASP.NET Web API, a controller is a class that handles HTTP requests. The public methods of the controller are called action methods or simply actions. When the Web API framework receives a request, it routes the request to an action. To determine which action to invoke, the framework uses a rou...