Arrow Computer

[Heinz Francis]

Unfortunatelypseudo-code is often used without documenting it, under the assumption that it will be "obvious" to the reader what the code means. As you have discovered, what is and isn't obvious to the reader obviously depends on the reader!

Arrows generally are used to indicate that "some thing" is "flowing" in the direction of the arrow. A rightwards arrow typically means "goes to" in the sense of a mapping or a function. A leftwards arrow typically means "becomes" or "let" or "draws from". However, arrows can also indicate message sends or receiving messages. You have to be aware of the context.

This code looks like it is simple imperative structured programming code, so the "assignment" meaning is the more likely interpretation, but if this where pseudo-code for some process calculus, an asynchronous, concurrent, parallel, or distributed algorithm or data structure, or something along those lines, it could likely also mean "blocks until it receives a message" or something like that.

The first one also means assignment, but it is interpreted to mean that j takes all the values on the right-hand side, one after the other. In other words, this is a FOREACH iterator loop. (Scala actually uses the leftwards arrow in precisely this meaning in its for comprehensions.)

There is an anecdote I recall from very long ago about some famous computer scientist, perhaps Dijkstra, having become outraged during some seminar lecture and loudly yelling out "becomes! becomes!" at the point when the presenter had written or projected an "a = b + c" expression which he then began reading out loud as "a equals b plus c".

Here is a true story of my own: he first time I had ever seen a computer program, which was written in line numbered BASIC and contained a few lines of variable assignments, I was really puzzled because I thought that this was a system of equations being declared for the machine to solve! "But how on Earth can X be equal to X + 1??!" I thought.

I think this is often used in pseudo-code to distinguish between equality and assignment because different languages have different rules for how this works. For example, = can be an assignment or copy in c++ and javascript has a table of rules on how equality checks works. The point of pseudocode is not to depend on language conventions and to attempt to be unambiguous in what the code does.

We've all seen the computers of Felicity Smoak and every other similar character with similar environment in Hollywood shows. Is everything going on on the computer screen real software applications or just animation?

My old company used to do this a lot in demonstrating software - it would all be mocked up screens and the sales people would simply move the mouse to the right place and click - customers were fooled into thinking it was real software being used.

I guess that computer screens can also be added digitally in post-production. This provides a was of obviating annoying physical issues like reflected studio lighting - or maybe there's just an automagical anti reflective coating on computer screens for use in film/TV studios.

In season 5, I caught a glimpse of what looked like a spreadsheet on screen when Felicity was doing her thing. It stuck out because the current plot didn't support a spreadsheet being the mysterious hacker juice. I briefly looked scanned through the episodes but couldn't find the clip again. It was especially fast; I had to pause and rewind several times to catch it on screen to study it.

Long story short, it looked like Excel 2016 or Office 365's toolbar, and the window looked like a Windows 10 window. Given the dark color scheme, it's possible that it's a skinned Windows 10. At least, that shot in that episode was.

Great advice that has been listed here, mostly it is an animation that is fed on their screen and nothing else. The real hacking stuff is mostly seen on Mr. Robot and the screens of Arrow and Flash are mostly nothing but CGI, or, as said, created temporary screens.

In computer science, arrows or bolts are a type class used in programming to describe computations in a pure and declarative fashion. First proposed by computer scientist John Hughes as a generalization of monads, arrows provide a referentially transparent way of expressing relationships between logical steps in a computation.[1] Unlike monads, arrows don't limit steps to having one and only one input. As a result, they have found use in functional reactive programming, point-free programming, and parsers among other applications.[1][2]

While arrows were in use before being recognized as a distinct class, it wasn't until 2000 that John Hughes first published research focusing on them. Until then, monads had proven sufficient for most problems requiring the combination of program logic in pure code. However, some useful libraries, such as the Fudgets library for graphical user interfaces and certain efficient parsers, defied rewriting in a monadic form.[1]

The formal concept of arrows was developed to explain these exceptions to monadic code, and in the process, monads themselves turned out to be a subset of arrows.[1] Since then, arrows have been an active area of research. Their underlying laws and operations have been refined several times, with recent formulations such as arrow calculus requiring only five laws.[3]

In category theory, the Kleisli categories of all monads form a proper subset of Hughes arrows.[1] While Freyd categories were believed to be equivalent to arrows for a time,[4] it has since been proven that arrows are even more general. In fact, arrows are not merely equivalent, but directly equal to enriched Freyd categories.[5]

Like all type classes, arrows can be thought of as a set of qualities that can be applied to any data type. In the Haskell programming language, arrows allow functions (represented in Haskell by -> symbol) to combine in a reified form. However, the actual term "arrow" may also come from the fact that some (but not all) arrows correspond to the morphisms (also known as "arrows" in category theory) of different Kleisli categories. As a relatively new concept, there is not a single, standard definition, but all formulations are logically equivalent, feature some required methods, and strictly obey certain mathematical laws.[6]

Arrows may be extended to fit specific situations by defining additional operations and restrictions. Commonly used versions include arrows with choice, which allow a computation to make conditional decisions, and arrows with feedback, which allow a step to take its own outputs as inputs. Another set of arrows, known as arrows with application, are rarely used in practice because they are actually equivalent to monads.[6]

Arrows have several benefits, mostly stemming from their ability to make program logic explicit yet concise. Besides avoiding side effects, purely functional programming creates more opportunities for static code analysis. This in turn can theoretically lead to better compiler optimizations, easier debugging, and features like syntax sugar.[6]

Although no program strictly requires arrows, they generalize away much of the dense function passing that pure, declarative code would otherwise require. They can also encourage code reuse by giving common linkages between program steps their own class definitions. The ability to apply to types generically also contributes to reusability and keeps interfaces simple.[6]

Arrows do have some disadvantages, including the initial effort of defining an arrow that satisfies the arrow laws. Because monads are usually easier to implement, and the extra features of arrows may be unnecessary, it is often preferable to use a monad.[6] Another issue, which applies to many functional programming constructs, is efficiently compiling code with arrows into the imperative style used by computer instruction sets.[citation needed]

Due to the requirement of having to define an arr function to lift pure functions, the applicability of arrows is limited. For example, bidirectional transformations cannot be arrows, because one would need to provide not only a pure function, but also its inverse, when using arr.[8] This also limits the use of arrows to describe push-based reactive frameworks that stop unnecessary propagation. Similarly, the use of pairs to tuple values together results in a difficult coding style that requires additional combinators to re-group values, and raises fundamental questions about the equivalence of arrows grouped in different ways. These limitations remain an open problem, and extensions such as Generalized Arrows[8] and N-ary FRP[9] explore these problems.

Much of the utility of arrows is subsumed by more general classes like Profunctor (which requires only pre- and postcomposition with functions), which have application in optics. An arrow is essentially a strong profunctor that is also a category, although the laws are slightly different.

I attempted to do a phone update....after a long while my phone did not restart.... It just had the apple pic with the black line under it... Tried to shut down my phone and when it came back on the top of the screen shows ' supportapple.com/iphone/restore'. Underneath this is a pic of a rectangle with a line under it (computer\monitor? ) and a charger cord with an arrow pointing to the pic.

Based on what you mentioned, your iPhone is now set to restore mode after trying to update the device. You'll see what you have on your own iPhone's display here: If you see the Restore screen on your iPhone, iPad, or iPod touch.

To explain (that wasn't very clear), if I'm on Facebook photo viewer, the arrow keys can be used to move to the next or previous photo. However, it feels as if the right arrow key is constantly down, as the viewer scrolls through all the photos. Another example is that in any text field, the cursor runs through the text to the end.

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