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Event-driven programming

In computer programming, event-driven programming is a programming paradigm in which the flow of the program is determined by events such as user actions, sensor outputs, or messages from other programs or threads. Event-driven programming is the dominant paradigm used in graphical user interfaces and other applications that are centered on performing certain actions in response to user input; this is true of programming for device drivers. In an event-driven application, there is a main loop that listens for events, triggers a callback function when one of those events is detected. In embedded systems, the same may be achieved using hardware interrupts instead of a running main loop. Event-driven programs can be written in any programming language, although the task is easier in languages that provide high-level abstractions, such as await and closures; because the code is for checking for events and the main loop are common amongst applications, many programming frameworks take care of their implementation and expect the user to provide only the code for the event handlers.

In this simple example, there may be a call to an event handler called OnKeyEnter that includes an argument with a string of characters, corresponding to what the user typed before hitting the ENTER key. To add two numbers, storage outside the event handler must be used; the implementation might look like below. While keeping track of history is trivial in a sequential program because event handlers execute in response to external events structuring the handlers to work when called in any order can require special attention and planning in an event-driven program; the first step in developing an event-driven program is to write a series of subroutines, or methods, called event-handler routines. These routines handle the events. For example, a single left-button mouse-click on a command button in a GUI program may trigger a routine that will open another window, save data to a database or exit the application. Many modern-day programming environments provide the programmer with event templates, allowing the programmer to focus on writing the event code.

The second step is to bind event handlers to events so that the correct function is called when the event takes place. Graphical editors combine the first two steps: double-click on a button, the editor creates an event handler associated with the user clicking the button and opens a text window so you can edit the event handler; the third step in developing an event-driven program is to write the main loop. This is a function that checks for the occurrence of events, calls the matching event handler to process it. Most event-driven programming environments provide this main loop, so it need not be provided by the application programmer. RPG, an early programming language from IBM, whose 1960s design concept was similar to event-driven programming discussed above, provided a built-in main I/O loop where the calculations responded in accordance to'indicators' that were set earlier in the cycle. In PL/I though a program itself may not be predominantly event-driven, certain abnormal events such as a hardware error, overflow or "program checks" may occur that prevent further processing.

Exception handlers may be provided by "ON statements" in callers to provide cleaning routines to clean up afterwards before termination, or to perform recovery operations and return to the interrupted procedure. Most existing GUI development tools and architectures rely on event-driven programming; the Java AWT framework processes all UI changes on a single thread, called the Event dispatching thread. All UI updates in the Java framework JavaFX occur on the JavaFX Application Thread. In addition, systems such as Node.js are event-driven. The design of those programs which rely on event-action model has been criticised, it has been suggested that the event-action model leads programmers to create error-prone, difficult to extend and excessively complex application code. Table-driven state machines have been advocated as a viable alternative. On the other hand, table-driven state machines themselves suffer from significant weaknesses including state explosion phenomena. A solution for this is to use Petri nets.

An event-driven approach is used in hardware description languages. A thread context only needs a CPU stack while processing an event; this is a finite-state machine approach. Autonomous peripheral operation Comparison of programming paradigms Dataflow programming DOM events Event-driven architecture Event stream processing Hardware description language Interrupt Inversion of control Message-oriented middleware Programming paradigm Publish–subscribe pattern Reactor pattern Signal programming Staged event-driven architecture Time-triggered system Virtual synchrony, a distributed execution model for event-driven programming Concurrency patterns presentation given at scaleconf Event-Driven Programming: Introduction, History, tutorial by Stephen Ferg Event Driven Programming, tutorial by Alan Gauld Event Collaboration, article by Martin Fowler Rethinking Swing Threading, article by Jonathan Simon The event driven programming style, article by Chris McDonald Event Driven Programming using Template Specialization, article by Christopher Diggins Schiffer, S..

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Nahant Life-Saving Station

The Nahant Life-Saving Station is a historic coastal rescue station at 96 Nahant Road in Nahant, Massachusetts. The station, which consists of a residence and an equipment building, was established in 1900 by the United States Life-Saving Service before being taken over by the United States Coast Guard in 1915; the station was discontinued in 1964, the facilities were converted recreational use by the Coast Guard. In 1999 the 1.4 acres parcel was turned over to the Town of Nahant. The station, one of twelve such surviving facilities in the state, was listed on the National Register of Historic Places in 2012; the town of Nahant is located on a tied island connected to the south shore of Cape Ann by a sandy north-south causeway. Near the southern end of this causeway there is an eastward projection known as Little Nahant; the Nahant Life-Saving Station is located on the east side of the causeway between Little Nahant and the rest of Nahant. The main station house is an imposing two-story wood frame structure, with a square tower at the southwest corner.

The building is in the Shingle style, with a hip roof, pierced by hip-roof dormers and a large cross-gabled section. The front facade has two inset porches with Tuscan columns at the sides; the interior of the building was arranged with the keeper's residence in the north, crew quarters in the south, a boat and equipment storage area in the center. The east facade has two pairs of double-doors for moving boats out to Nahant Bay to the east, while the west side has a single double door for launching boats to the west; this structure was built in 1900 by the United States Life-Saving Service to a design by Victor Mendeleff. To the main station's southeast is an equipment building a four-bay garage with Colonial Revival details; the stations was established in 1900, was one of 33 such stations built in the state. It is the only one that appears to not have been built to a standard plan, is one of only twelve to survive in any significant form, it was in service until 1964, longer than any other in the state except for the Point Allerton Station.

The Coast Guard converted the building to a recreational facility in 1964, in 1999 turned it over to the town. The town has restored the building to its appearance c. 1915. National Register of Historic Places listings in Essex County, Massachusetts

Howard Helmer

Howard Helmer is a chef, an advocate of cooking eggs. Raised in Chicago, he now lives in New York City. Helmer holds the Guinness world record for the fastest omelette cooker, having made 427 omelets in:30 minutes; this feat was accomplished in Atlanta, Georgia in 1990. He holds the world records for fastest omelet flipper. Helmer has made appearances on the Food Network and television programs around the world, he was a spokesperson for the American Egg Board and, prior to his retirement, worked with his successor to that role, Jeffrey Saad. In 2011, Helmer was invited to do a demonstration at the White House in a session called, "play with your food." American Egg Board

Super-Poincaré algebra

In theoretical physics, a super-Poincaré algebra is an extension of the Poincaré algebra to incorporate supersymmetry, a relation between bosons and fermions. They are examples of supersymmetry algebras, are Lie superalgebras, thus a super-Poincaré algebra is a Z2-graded vector space with a graded Lie bracket such that the part is a Lie algebra containing the Poincaré algebra, the odd part is built from spinors on which there is an anticommutation relation with values in the part. The Poincaré algebra describes the isometries of Minkowski spacetime. From the representation theory of the Lorentz group, it is known that the Lorentz group admits two inequivalent complex spinor representations, dubbed 2 and 2 ¯. Taking their tensor product, one obtains 2 ⊗ 2 ¯ = 3 ⊕ 1. One treats such a decomposition as relating to specific particles: so, for example, the pion, a chiral vector particle, is composed of a quark-anti-quark pair. However, one could identify 3 ⊕ 1 with Minkowski spacetime itself; this leads to a natural question: if Minkowski space-time belongs to the adjoint representation can Poincaré symmetry be extended to the fundamental representation?

Well, it can: this is the super-Poincaré algebra. There is a corresponding experimental question: if we live in the adjoint representation where is the fundamental representation hiding? This is the program of supersymmetry; the super-Poincaré algebra was first proposed in the context of the Haag–Łopuszański–Sohnius theorem, as a means of avoiding the conclusions of the Coleman–Mandula theorem. That is, the Coleman–Mandula theorem is a no-go theorem that states that the Poincaré algebra cannot be extended with additional symmetries that might describe the internal symmetries of the observed physical particle spectrum. However, the Coleman–Mandula theorem assumed that the algebra extension would be by means of a commutator; the proposal was to consider a supersymmetry algebra, defined as the semidirect product of a central extension of the super-Poincaré algebra by a compact Lie algebra of internal symmetries. The simplest supersymmetric extension of the Poincaré algebra contains two Weyl spinors with the following anti-commutation relation: = 2 σ μ α β ˙ P μ and all other anti-commutation relations between the Qs and Ps vanish.

In the above expression P μ are the generators of translation and σ μ are the Pauli matrices. The index α runs over the values α = 1, 2. A dot is used over the index β ˙ to remind that this index transforms according to the inequivalent conjugate spinor representation; the Pauli matrices can be considered to be a direct manifestation of the Littlewood-Richardson rule mentioned before: they indicate how the tensor product 2 ⊗ 2 ¯ of the two spinors can be re-expressed as a vector. The index μ of course ranges over the space-time dimensions μ = 0, 1, 2, 3, it is convenient to work with Dirac spinors instead of Weyl spinors. The Dirac matrices are thus four-dimensional, can be expressed as direct sums of the Pauli matrices; the tensor product gives an algebraic relation to the Minkowski metric g μ ν, expressed as: = 2 g μ ν and σ μ ν = i 2 This gives the full algebra = 1 2 α β

Großer Beil

The Großer Beil, is a 2,309 m high mountain at the head of the Wildschönau valley in the Austrian state of Tyrol. It belongs to the Kitzbühel Alps and is the highest summit on the ridge that separates the Wildschönau from the neighbouring valley of the Alpbach to the west. Around 500 metres north is the 2,189 m high Seekopf and a further 500 metres beyond, the Kleine Beil at 2,197 m; the next mountain to the south is the 2,216 m high Gressenstein. On the other side of the valley is the Wildkarspitze; the Großer Beil is a popular hiking mountain and may be reached on marked trails from the north or south. The usual start point is the Schönangeralm at the head of the Wildschönau valley behind Auffach. In winter the Großer Beil is a popular ski tour; the name of the mountain is not derived from the German word Beil but from a dialect word for a place near which animals are held during a hunt

Vicken Parsons

Vicken Parsons, Lady Gormley, is a British artist painting in oils, but making sculptures. Her works are displayed in Tate Britain, are in the collections of the Arts Council and the Scottish National Gallery of Modern Art, she attended the Slade School of Fine Art, in London. She is represented by Alan Cristea Gallery and Ivorypress, Madrid. Parsons' solo exhibitions have included Galerie Christine König, Kettle's Yard, the Alan Cristea Gallery, Tate St Ives, her work has been exhibited at the Royal Academy, the Institute of Contemporary Arts, Tate Modern, Southampton City Art Gallery and Kunsthalle Mannheim. Her husband is sculptor Sir Antony Gormley, O. B. E.. Vicken met Gormley while attending the Slade, they married in 1980, she worked as his assistant. Gormley said of her: For the first 15 years she was my primary assistant, she did all of the body moulding... I think there are a lot of myths that art is made by lone men... I just feel so lucky and so blessed that I have such a strong supporter, lover, fellow artist.

The couple have a daughter and two sons. 5 paintings by or after Vicken Parsons at the Art UK site