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60-772: ArkUI 3.0 is declarative in eTS (extended TypeScript) in HarmonyOS 3.0, followed by main ArkTS programming language in HarmonyOS 3.1, contrasting with the imperative syntax used in Java development in earlier versions of HarmonyOS in HarmonyOS 1.0 and 2.0. ArkUI allows for 2D drawing as well as 3D drawing, animations, event handling , Service Card widgets, and data binding . ArkUI automatically synchronizes between UI views and data. ArkUI integrates with DevEco Studio IDE to provide for real-time previews during editing, alongside support for debugging and other development features. ArkJS

120-431: A declarative programming language. Within an imperative programming language , a control flow statement is a statement that results in a choice being made as to which of two or more paths to follow. For non-strict functional languages, functions and language constructs exist to achieve the same result, but they are usually not termed control flow statements. A set of statements is in turn generally structured as

180-474: A block , which in addition to grouping, also defines a lexical scope . Interrupts and signals are low-level mechanisms that can alter the flow of control in a way similar to a subroutine , but usually occur as a response to some external stimulus or event (that can occur asynchronously ), rather than execution of an in-line control flow statement. At the level of machine language or assembly language , control flow instructions usually work by altering

240-453: A first-class object in the program. Although pure functional languages are non-imperative, they often provide a facility for describing the effect of a function as a series of steps. Other functional languages, such as Lisp , OCaml and Erlang , support a mixture of procedural and functional programming. Some logic programming languages, such as Prolog , and database query languages, such as SQL, while declarative in principle, also support

300-532: A server ) should loop forever, handling events as they occur, only stopping when the process is terminated by an operator. Infinite loops can be implemented using other control flow constructs. Most commonly, in unstructured programming this is jump back up (goto), while in structured programming this is an indefinite loop (while loop) set to never end, either by omitting the condition or explicitly setting it to true, as while (true) ... . Some languages have special constructs for infinite loops, typically by omitting

360-418: A declarative programming style. In logic programming, programs consist of sentences expressed in logical form, and computation uses those sentences to solve problems, which are also expressed in logical form. In a pure functional language , such as Haskell , all functions are without side effects , and state changes are only represented as functions that transform the state, which is explicitly represented as

420-402: A desire to skip the remainder of the loop body and continue with the next iteration of the loop. Some languages provide a statement such as continue (most languages), skip , cycle (Fortran), or next (Perl and Ruby), which will do this. The effect is to prematurely terminate the innermost loop body and then resume as normal with the next iteration. If the iteration is the last one in

480-431: A final keyword. Conditional expressions and conditional constructs are features of a programming language that perform different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false. Less common variations include: Switch statements (or case statements , or multiway branches ) compare a given value with specified constants and take action according to

540-467: A function to output the first n square numbers in Racket can be done accordingly: The map function accepts a function and a list; the output is a list of results of the input function on each element of the input list. ML (1973) stands for "Meta Language." ML is statically typed, and function arguments and return types may be annotated. ML is not as bracket-centric as Lisp , and instead uses

600-464: A goal is a logical consequence of the program, or by showing that the goal is true in a model defined by the program. Prolog computes by reducing goals to subgoals, top-down using backward reasoning , whereas most Datalog systems compute bottom-up using forward reasoning . Answer set programs typically use SAT solvers to generate a model of the program. Models, or mathematical representations, of physical systems may be implemented in computer code that

660-545: A label is an identifier , usually appearing at the start of a line and immediately followed by a colon. For example, in C: The language ALGOL 60 allowed both whole numbers and identifiers as labels (both linked by colons to the following statement), but few if any other ALGOL variants allowed whole numbers. Early Fortran compilers only allowed whole numbers as labels. Beginning with Fortran-90, alphanumeric labels have also been allowed. The goto statement (a combination of

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720-509: A multilevel break or continue – this was proposed in PEP 3136 , and rejected on the basis that the added complexity was not worth the rare legitimate use. The notion of multi-level breaks is of some interest in theoretical computer science , because it gives rise to what is today called the Kosaraju hierarchy . In 1973 S. Rao Kosaraju refined the structured program theorem by proving that it

780-619: A procedural style of programming. Declarative programming is an umbrella term that includes a number of better-known programming paradigms . Constraint programming states relations between variables in the form of constraints that specify the properties of the target solution. The set of constraints is solved by giving a value to each variable so that the solution is consistent with the maximum number of constraints. Constraint programming often complements other paradigms: functional, logical, or even imperative programming. Well-known examples of declarative domain-specific languages (DSLs) include

840-405: A separate area around 1977. Syntactically and semantically , it is a subset of Prolog. But because it does not have compound terms , it is not Turing-complete . Most Datalog systems execute programs bottom-up, using rules to reason forwards , deriving new facts from existing facts, and terminating when there are no new facts that can be derived, or when the derived facts unify with the query. In

900-457: A set or collection. Scala has for-expressions , which generalise collection-controlled loops, and also support other uses, such as asynchronous programming . Haskell has do-expressions and comprehensions, which together provide similar function to for-expressions in Scala. General iteration constructs such as C's for statement and Common Lisp 's do form can be used to express any of

960-401: A state variable which is tested to break out another level; exceptions, which are caught at the level being broken out to; placing the nested loops in a function and using return to effect termination of the entire nested loop; or using a label and a goto statement. C does not include a multilevel break, and the usual alternative is to use a goto to implement a labeled break. Python does not have

1020-493: A statement without disrupting the control flow. In other words, they were composable . (Later developments, such as non-strict programming languages – and more recently, composable software transactions – have continued this strategy, making components of programs even more freely composable.) Some academics took a purist approach to the Böhm–Jacopini result and argued that even instructions like break and return from

1080-693: A webpage - it specifies neither control flow for rendering a page nor the page's possible interactions with a user . As of 2013 , some software systems combine traditional user-interface markup languages (such as HTML) with declarative markup that defines what (but not how) the back-end server systems should do to support the declared interface. Such systems, typically using a domain-specific XML namespace , may include abstractions of SQL database syntax or parameterized calls to web services using representational state transfer (REST) and SOAP . Functional programming languages such as Haskell , Scheme , and ML evaluate expressions via function application. Unlike

1140-488: A wider variety of syntax to codify the relationship between code elements, rather than appealing to list ordering and nesting to express everything. The following is an application of times_10 : It returns "20 : int", that is, 20 , a value of type int . Like Lisp , ML is tailored to process lists, though all elements of a list must be the same type. Prolog (1972) stands for "PROgramming in LOGic." It

1200-400: Is an open-source UI software development kit which is the extension of ArkUI created by Huawei for building cross platform applications , including Android , iOS , OpenHarmony and HarmonyOS NEXT targets. Web platform support with ArkJS was released on December 8, 2023. ArkUI-X consists of both a UI language and a rendering engine. System components are built-in components within

1260-676: Is at the start, the body may be skipped completely; if it is at the end, the body is always executed at least once. A control break is a value change detection method used within ordinary loops to trigger processing for groups of values. Values are monitored within the loop and a change diverts program flow to the handling of the group event associated with them. Several programming languages (e.g., Ada , D , C++11 , Smalltalk , PHP , Perl , Object Pascal , Java , C# , MATLAB , Visual Basic , Ruby , Python , JavaScript , Fortran 95 and later) have special constructs which allow implicit looping through all elements of an array, or all members of

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1320-407: Is declarative. The code contains a number of equations, not imperative assignments, that describe ("declare") the behavioral relationships. When a model is expressed in this formalism, a computer is able to perform algebraic manipulations to best formulate the solution algorithm. The mathematical causality is typically imposed at the boundaries of the physical system, while the behavioral description of

1380-1289: Is designed for web development with a Vue 2-like syntax, providing a familiar environment for web developers using JS and CSS. ArkJS incorporates the HarmonyOS Markup Language (HML), which allows attributes prefixed with @ for MVVM architectural pattern . During HDC 2021 on October 22, 2021, the HarmonyOS 3.0 developer preview introduced ArkUI 3.0 for eTS, JS programming languages with ArkCompiler. Compared to previous versions of ArkUI 1.0 and 2.0 under imperative development with Java in earlier versions of HarmonyOS. During HDC 2022 HarmonyOS 3.1 in November 2022, Huawei ArkUI evolved into full declarative development featuring declarative UI capabilities, improved layout ability, component capability improvement and others. In April 2023, HarmonyOS 3.1 Beta 1 build included ArkUI declarative 2D and 3D drawing capabilities. The upgrade also improves layout, component, and app state management capabilities. During HDC 2023, August 2023, Huawei announced HarmonyOS 4.0 improvements of ArkUI with ArkTS alongside native HarmonyOS NEXT software development using Ark Engine with ArkGraphics 2D and ArkGraphics 3D . Also,

1440-477: Is found. Some programming languages provide a statement such as break (most languages), Exit (Visual Basic), or last (Perl), which effect is to terminate the current loop immediately, and transfer control to the statement immediately after that loop. Another term for early-exit loops is loop-and-a-half . The following example is done in Ada which supports both early exit from loops and loops with test in

1500-553: Is met, or indefinitely . When one of those items is itself also a loop, it is called a "nested loop". In functional programming languages, such as Haskell and Scheme , both recursive and iterative processes are expressed with tail recursive procedures instead of looping constructs that are syntactic. Most programming languages have constructions for repeating a loop a certain number of times. In most cases counting can go downwards instead of upwards and step sizes other than 1 can be used. In these examples, if N < 1 then

1560-485: Is often defined as any style of programming that is not imperative. A number of other common definitions attempt to define it by simply contrasting it with imperative programming. For example: These definitions overlap substantially. Declarative programming is a non-imperative style of programming in which programs describe their desired results without explicitly listing commands or steps that must be performed. Functional and logic programming languages are characterized by

1620-466: Is possible to avoid adding additional variables in structured programming, as long as arbitrary-depth, multi-level breaks from loops are allowed. Furthermore, Kosaraju proved that a strict hierarchy of programs exists: for every integer n , there exists a program containing a multi-level break of depth n that cannot be rewritten as a program with multi-level breaks of depth less than n without introducing added variables. One can also return out of

1680-423: The main_pages.json file before being invoked. Declarative programming In computer science , declarative programming is a programming paradigm —a style of building the structure and elements of computer programs—that expresses the logic of a computation without describing its control flow . Many languages that apply this style attempt to minimize or eliminate side effects by describing what

1740-548: The DPLL algorithm to generate one or more models of the program. Its applications are oriented towards solving difficult search problems and knowledge representation . Control flow In computer science , control flow (or flow of control ) is the order in which individual statements , instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an imperative programming language from

1800-440: The factorial function can be defined as follows: This defines the factorial function using its recursive definition. In contrast, it is more typical to define a procedure for an imperative language. In lisps and lambda calculus, functions are generally first-class citizens . Loosely, this means that functions can be inputs and outputs for other functions. This can simplify the definition of some functions. For example, writing

1860-479: The program counter . For some central processing units (CPUs), the only control flow instructions available are conditional or unconditional branch instructions, also termed jumps. The kinds of control flow statements supported by different languages vary, but can be categorized by their effect: A label is an explicit name or number assigned to a fixed position within the source code , and which may be referenced by control flow statements appearing elsewhere in

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1920-642: The yacc parser generator input language, QML , the Make build specification language, Puppet 's configuration management language, regular expressions , Datalog , answer set programming and a subset of SQL (SELECT queries, for example). DSLs have the advantage of being useful while not necessarily needing to be Turing-complete , which makes it easier for a language to be purely declarative. Many markup languages such as HTML , MXML , XAML , XSLT or other user-interface markup languages are often declarative. HTML, for example, only describes what should appear on

1980-479: The 1950s, computer memories were very small by current standards so subroutines were used mainly to reduce program size. A piece of code was written once and then used many times from various other places in a program. Today, subroutines are more often used to help make a program more structured, e.g., by isolating some algorithm or hiding some data access method. If many programmers are working on one program, subroutines are one kind of modularity that can help divide

2040-574: The ArkUI framework, categorized into container components and basic components. For example, Row and Column are container components that can hold other components, while Text and Button are basic components. The following is an example of a simple Hello World program. It is standard practice in ArkUI to separate the application struct and views into different structs, with the main view named Index . The @ohos.router routing library implements page transitions, which must be declared in

2100-772: The English words go and to , and pronounced accordingly) is the most basic form of unconditional transfer of control. Although the keyword may either be in upper or lower case depending on the language, it is usually written as: The effect of a goto statement is to cause the next statement to be executed to be the statement appearing at (or immediately after) the indicated label. Goto statements have been considered harmful by many computer scientists, notably Dijkstra . The terminology for subroutines varies; they may alternatively be known as routines, procedures, functions (especially if they return results) or methods (especially if they belong to classes or type classes ). In

2160-571: The ML and Lisp families, are not purely functional , and thus allow the introduction of stateful effects in programs. Makefiles, for example, specify dependencies in a declarative fashion, but include an imperative list of actions to take as well. Similarly, yacc specifies a context free grammar declaratively, but includes code snippets from a host language, which is usually imperative (such as C ). Logic programming languages, such as Prolog , Datalog and answer set programming , compute by proving that

2220-477: The Pascal-provided control structures, the correct solution was given by only 20% of the subjects, while no subject wrote incorrect code for this problem if allowed to write a return from the middle of a loop. Most programming languages with control structures have an initial keyword which indicates the type of control structure involved. Languages then divide as to whether or not control structures have

2280-704: The above example is linked to the for statement, and not the inner if statement. Both Python's for and while loops support such an else clause, which is executed only if early exit of the loop has not occurred. Some languages support breaking out of nested loops; in theory circles, these are called multi-level breaks. One common use example is searching a multi-dimensional table. This can be done either via multilevel breaks (break out of N levels), as in bash and PHP, or via labeled breaks (break out and continue at given label), as in Go, Java and Perl. Alternatives to multilevel breaks include single breaks, together with

2340-487: The above example, a typical Datalog system would first derive the new facts: Using these facts, it would then derive the additional fact: It would then terminate, both because no new, additional facts can be derived, and because the newly derived fact unifies with the query Datalog has been applied to such problems as data integration , information extraction , networking , security , cloud computing and machine learning . Answer set programming (ASP) evolved in

2400-450: The above sorts of loops, and others, such as looping over some number of collections in parallel. Where a more specific looping construct can be used, it is usually preferred over the general iteration construct, since it often makes the purpose of the expression clearer. Infinite loops are used to assure a program segment loops forever or until an exceptional condition arises, such as an error. For instance, an event-driven program (such as

2460-614: The addition of Boolean variables (true/false flags). Later authors showed that choice can be replaced by loops (and yet more Boolean variables). That such minimalism is possible does not mean that it is necessarily desirable; computers theoretically need only one machine instruction (subtract one number from another and branch if the result is negative), but practical computers have dozens or even hundreds of machine instructions. Other research showed that control structures with one entry and one exit were much easier to understand than any other form, mainly because they could be used anywhere as

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2520-543: The answer substitution X = tom . Prolog executes programs top-down, using SLD resolution to reason backwards , reducing goals to subgoals. In this example, it uses the last rule of the program to reduce the goal of answering the query eat ( X , jerry ) to the subgoals of first finding an X such that big ( X ) holds and then of showing that small ( jerry ) holds. It repeatedly uses rules to further reduce subgoals to other subgoals, until it eventually succeeds in unifying all subgoals with facts in

2580-436: The body of loop may execute once (with I having value 1) or not at all, depending on the programming language. In many programming languages, only integers can be reliably used in a count-controlled loop. Floating-point numbers are represented imprecisely due to hardware constraints, so a loop such as might be repeated 9 or 10 times, depending on rounding errors and/or the hardware and/or the compiler version. Furthermore, if

2640-666: The company announced a cross platform extension of ArkUI called ArkUI-X which would allow developers to run applications across Android, iOS and HarmonyOS under one project using DevEco Studio IDE and Visual Studio Code plugins. On January 18, 2024, during HarmonyOS Ecology Conference, Huawei revealed the HarmonyOS NEXT software stack, that included ArkUI/ArkUI-X programming framework with the Ark Compiler / BiSheng Compiler / Ark Runtime compiler & runtime, for both ArkTS and incoming Cangjie programming language . ArkUI-X

2700-400: The condition from an indefinite loop. Examples include Ada ( loop ... end loop ), Fortran ( DO ... END DO ), Go ( for { ... } ), and Ruby ( loop do ... end ). Often, an infinite loop is unintentionally created by a programming error in a condition-controlled loop, wherein the loop condition uses variables that never change within the loop. Sometimes within the body of a loop there is

2760-487: The default case as a glob matching any string. Case logic can also be implemented in functional form, as in SQL 's decode statement. A loop is a sequence of statements which is specified once but which may be carried out several times in succession. The code "inside" the loop (the body of the loop, shown below as xxx ) is obeyed a specified number of times, or once for each of a collection of items, or until some condition

2820-404: The first constant to match. There is usually a provision for a default action ("else", "otherwise") to be taken if no match succeeds. Switch statements can allow compiler optimizations, such as lookup tables . In dynamic languages , the cases may not be limited to constant expressions, and might extend to pattern matching , as in the shell script example on the right, where the *) implements

2880-404: The increment of X occurs by repeated addition, accumulated rounding errors may mean that the value of X in each iteration can differ quite significantly from the expected sequence 0.1, 0.2, 0.3, ..., 1.0. Most programming languages have constructions for repeating a loop until some condition changes. Some variations test the condition at the start of the loop; others test it at the end. If the test

2940-402: The late 1990s, based on the stable model (answer set) semantics of logic programming. Like Datalog, it is a subset of Prolog; and, because it does not have compound terms, it is not Turing-complete. Most implementations of ASP execute a program by first "grounding" the program, replacing all variables in rules by constants in all possible ways, and then using a propositional SAT solver, such as

3000-402: The loop, the effect is to terminate the entire loop early. Some languages, like Perl and Ruby, have a redo statement that restarts the current iteration from the start. Ruby has a retry statement that restarts the entire loop from the initial iteration. When using a count-controlled loop to search through a table, it might be desirable to stop searching as soon as the required item

3060-429: The middle . Both features are very similar and comparing both code snippets will show the difference: early exit must be combined with an if statement while a condition in the middle is a self-contained construct. Python supports conditional execution of code depending on whether a loop was exited early (with a break statement) or not by using an else-clause with the loop. For example, The else clause in

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3120-456: The middle of loops are bad practice as they are not needed in the Böhm–Jacopini proof, and thus they advocated that all loops should have a single exit point. This purist approach is embodied in the language Pascal (designed in 1968–1969), which up to the mid-1990s was the preferred tool for teaching introductory programming in academia. The direct application of the Böhm–Jacopini theorem may result in additional local variables being introduced in

3180-851: The program must accomplish in terms of the problem domain , rather than describing how to accomplish it as a sequence of the programming language primitives (the how being left up to the language's implementation ). This is in contrast with imperative programming , which implements algorithms in explicit steps. Declarative programming often considers programs as theories of a formal logic , and computations as deductions in that logic space. Declarative programming may greatly simplify writing parallel programs . Common declarative languages include those of database query languages (e.g., SQL , XQuery ), regular expressions , logic programming (e.g. Prolog , Datalog , answer set programming ), functional programming , configuration management , and algebraic modeling systems. Declarative programming

3240-467: The program. This backward reasoning, goal-reduction strategy treats rules in logic programs as procedures, and makes Prolog both a declarative and procedural programming language. The broad range of Prolog applications is highlighted in the Year of Prolog Book, celebrating the 50 year anniversary of Prolog. The origins of Datalog date back to the beginning of logic programming, but it was identified as

3300-409: The related but more imperative paradigm of procedural programming , functional programming places little emphasis on explicit sequencing. Instead, computations are characterised by various kinds of recursive higher-order function application and composition , and as such can be regarded simply as a set of mappings between domains and codomains . Many functional languages, including most of those in

3360-559: The source code. A label marks a position within source code and has no other effect. Line numbers are an alternative to a named label used in some languages (such as BASIC ). They are whole numbers placed at the start of each line of text in the source code. Languages which use these often impose the constraint that the line numbers must increase in value in each following line, but may not require that they be consecutive. For example, in BASIC: In other languages such as C and Ada ,

3420-471: The structured chart, and may also result in some code duplication . Pascal is affected by both of these problems and according to empirical studies cited by Eric S. Roberts , student programmers had difficulty formulating correct solutions in Pascal for several simple problems, including writing a function for searching an element in an array. A 1980 study by Henry Shapiro cited by Roberts found that using only

3480-449: The system itself is declarative or acausal. Declarative modeling languages and environments include Analytica , Modelica and Simile . Lisp is a family of programming languages loosely inspired by mathematical notation and Alonzo Church 's lambda calculus . Some dialects, such as Common Lisp , are primarily imperative but support functional programming. Others, such as Scheme , are designed for functional programming. In Scheme,

3540-619: The work. In structured programming, the ordered sequencing of successive commands is considered one of the basic control structures, which is used as a building block for programs alongside iteration, recursion and choice. In May 1966, Böhm and Jacopini published an article in Communications of the ACM which showed that any program with goto s could be transformed into a goto-free form involving only choice (IF THEN ELSE) and loops (WHILE condition DO xxx), possibly with duplicated code and/or

3600-436: Was developed for natural language question answering , using SL resolution both to deduce answers to queries and to parse and generate natural language sentences. The building blocks of a Prolog program are facts and rules . Here is a simple example: Given this program, the query eat ( tom , jerry ) succeeds, while eat ( jerry , tom ) fails. Moreover, the query eat ( X , jerry ) succeeds with

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