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In computing science and informatics, nesting [1] is where information is organized in layers, or where objects contain other similar objects. It almost always refers to self-similar or recursive structures in some sense.
Nesting can mean:
In a spreadsheet functions can be nested one into another, making complex formulas. The function wizard of the OpenOffice.org Calc application allows to navigate through multiple levels of nesting,[ further explanation needed ] letting the user to edit (and possibly correct) each one of them separately.
For example:
=IF(SUM(C8:G8)=0,"Y","N")
In this Microsoft Excel formula, the SUM function is nested inside the IF function. First, the formula calculates the sum of the numbers in the cells from C8 to G8. It then decides whether the sum is 0, and it displays the letter Y if the sum is 0, and the letter N if it is not.
Naturally, to allow the mathematical resolution of these chained (or better: nested) formulas, the inner expressions must be previously evaluated, and this outward direction is essential because the results that the internal functions return are temporarily used as entry data for the external ones.
Due to the potential accumulation of parentheses in only one code line, editing and error detecting (or debugging) can become somehow awkward. That is why modern programming environments -as well as spreadsheet programs- highlight in bold type the pair corresponding to the current editing position. The (automatic) balancing control of the opening and closing parenthesis is known as brace match checking.
In structured programming languages, nesting is related to the enclosing of control structures one into another, usually indicated through different indentation levels within the source code, as it is shown in this simple BASIC function:
functionLookupCode(sCodeasstring)asintegerdimiReturnValueasintegerdimsLine,sPathasstringsPath="C:\Test.dsv"ifFileExists(sPath)thenopensPathforinputas#1dowhilenotEOF(1)lineinput#1,sLineifsCode=left(sLine,3)then'Action(s) to be carried outEndifloopclose#1EndifLookupCode=iReturnValueendfunctionIn this small and simple example, the conditional block “if... then... end if” is nested inside the “do while... loop” one.
Some languages such as Pascal and Ada have no restrictions on declarations depending on the nesting level, allowing precisely nested subprograms or even nested packages (Ada). Here is an example of both (simplified from a real case):
-- Getting rid of the global variables issue (cannot be used in parallel)-- from a set of old sources, without the need to change that code's-- logic or structure.--procedureNesting_example_1istypeBuffer_typeisarray(Integerrange<>)ofInteger;procedureDecompress(compressed: inBuffer_type;decompressed: outBuffer_type)is-- Here are the legacy sources, translated:packageX_Globalsisindex_in,index_out:Integer;-- *** ^ These variables are local to Decompress.-- *** Now Decompress is task-safe.endX_Globals;-- Methods 1,2,3,... (specifications)packageX_Method_1isprocedureDecompress_1;endX_Method_1;-- Methods 1,2,3,... (code)packagebodyX_Method_1isuseX_Globals;procedureDecompress_1isbeginindex_in:=compressed'First;-- Here, the decompression code, method 1endDecompress_1;endX_Method_1;-- End of the legacy sourcesbeginX_Method_1.Decompress_1;endDecompress;test_in,test_out:Buffer_type(1..10_000);beginDecompress(test_in,test_out);endNesting_example_1;Nested data structures are also commonly encountered in programming.
In the functional programming languages, such as Lisp, a list data structure exists as does a simpler atom data structure. [2]
(ATOMS)The atoms in the list are A, T, O, M, and S.
(((NESTED)LISTS)(CAN)(BE)UNNECESSARILY(COMPLEX))
Erlang is a general-purpose, concurrent, functional programming language, and a garbage-collected runtime system. The term Erlang is used interchangeably with Erlang/OTP, or Open Telecom Platform (OTP), which consists of the Erlang runtime system, several ready-to-use components (OTP) mainly written in Erlang, and a set of design principles for Erlang programs.
Recursion occurs when a thing is defined in terms of itself or of its type. Recursion is used in a variety of disciplines ranging from linguistics to logic. The most common application of recursion is in mathematics and computer science, where a function being defined is applied within its own definition. While this apparently defines an infinite number of instances, it is often done in such a way that no infinite loop or infinite chain of references can occur.
OCaml is a general-purpose, multi-paradigm programming language which extends the Caml dialect of ML with object-oriented features. OCaml was created in 1996 by Xavier Leroy, Jérôme Vouillon, Damien Doligez, Didier Rémy, Ascánder Suárez, and others.
In computer science, control flow 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 a declarative programming language.
In computer programming, the scope of a name binding is the part of a program where the name binding is valid; that is, where the name can be used to refer to the entity. In other parts of the program, the name may refer to a different entity, or to nothing at all. Scope helps prevent name collisions by allowing the same name to refer to different objects – as long as the names have separate scopes. The scope of a name binding is also known as the visibility of an entity, particularly in older or more technical literature—this is from the perspective of the referenced entity, not the referencing name.
In programming languages, a closure, also lexical closure or function closure, is a technique for implementing lexically scoped name binding in a language with first-class functions. Operationally, a closure is a record storing a function together with an environment. The environment is a mapping associating each free variable of the function with the value or reference to which the name was bound when the closure was created. Unlike a plain function, a closure allows the function to access those captured variables through the closure's copies of their values or references, even when the function is invoked outside their scope.
Standard ML (SML) is a general-purpose, modular, functional programming language with compile-time type checking and type inference. It is popular among compiler writers and programming language researchers, as well as in the development of theorem provers.
Generic programming is a style of computer programming in which algorithms are written in terms of types to-be-specified-later that are then instantiated when needed for specific types provided as parameters. This approach, pioneered by the ML programming language in 1973, permits writing common functions or types that differ only in the set of types on which they operate when used, thus reducing duplication. Such software entities are known as generics in Ada, C#, Delphi, Eiffel, F#, Java, Nim, Python, Go, Rust, Swift, TypeScript and Visual Basic .NET. They are known as parametric polymorphism in ML, Scala, Julia, and Haskell ; templates in C++ and D; and parameterized types in the influential 1994 book Design Patterns.
In computer science, a pointer is an object in many programming languages that stores a memory address. This can be that of another value located in computer memory, or in some cases, that of memory-mapped computer hardware. A pointer references a location in memory, and obtaining the value stored at that location is known as dereferencing the pointer. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number and reading the text found on that page. The actual format and content of a pointer variable is dependent on the underlying computer architecture.
In most computer programming languages, a while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.
In computer science, a tail call is a subroutine call performed as the final action of a procedure. If the target of a tail is the same subroutine, the subroutine is said to be tail recursive, which is a special case of direct recursion. Tail recursion is particularly useful, and is often easy to optimize in implementations.
In computer programming, a nested function is a function which is defined within another function, the enclosing function. Due to simple recursive scope rules, a nested function is itself invisible outside of its immediately enclosing function, but can see (access) all local objects of its immediately enclosing function as well as of any function(s) which, in turn, encloses that function. The nesting is theoretically possible to unlimited depth, although only a few levels are normally used in practical programs.
xHarbour is a free multi-platform extended Clipper compiler, offering multiple graphic terminals (GTs), including console drivers, GUIs, and hybrid console/GUIs. xHarbour is backward-compatible with Clipper and supports many language syntax extensions, greatly extended run-time libraries, and extensive third party support.
In computer science, a call stack is a stack data structure that stores information about the active subroutines of a computer program. This kind of stack is also known as an execution stack, program stack, control stack, run-time stack, or machine stack, and is often shortened to just "the stack". Although maintenance of the call stack is important for the proper functioning of most software, the details are normally hidden and automatic in high-level programming languages. Many computer instruction sets provide special instructions for manipulating stacks.
Harbour is a computer programming language, primarily used to create database/business programs. It is a modernized, open sourced and cross-platform version of the older Clipper system, which in turn developed from the dBase database market of the 1980s and 1990s.
In computer science, recursion is a method of solving a computational problem where the solution depends on solutions to smaller instances of the same problem. Recursion solves such recursive problems by using functions that call themselves from within their own code. The approach can be applied to many types of problems, and recursion is one of the central ideas of computer science.
The power of recursion evidently lies in the possibility of defining an infinite set of objects by a finite statement. In the same manner, an infinite number of computations can be described by a finite recursive program, even if this program contains no explicit repetitions.
This is an overview of Fortran 95 language features. Included are the additional features of TR-15581:Enhanced Data Type Facilities, which have been universally implemented. Old features that have been superseded by new ones are not described – few of those historic features are used in modern programs although most have been retained in the language to maintain backward compatibility. The current standard is Fortran 2018; many of its new features are still being implemented in compilers. The additional features of Fortran 2003, Fortran 2008 and Fortran 2018 are described by Metcalf, Reid and Cohen.
In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed.
PL/SQL is Oracle Corporation's procedural extension for SQL and the Oracle relational database. PL/SQL is available in Oracle Database, Times Ten in-memory database, and IBM Db2. Oracle Corporation usually extends PL/SQL functionality with each successive release of the Oracle Database.
Lisp Flavored Erlang (LFE) is a functional, concurrent, garbage collected, general-purpose programming language and Lisp dialect built on Core Erlang and the Erlang virtual machine (BEAM). LFE builds on Erlang to provide a Lisp syntax for writing distributed, fault-tolerant, soft real-time, non-stop applications. LFE also extends Erlang to support metaprogramming with Lisp macros and an improved developer experience with a feature-rich read–eval–print loop (REPL). LFE is actively supported on all recent releases of Erlang; the oldest version of Erlang supported is R14.