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Dangling Else
The dangling else is a problem in programming of parser generators in which an optional else clause in an if–then(–else) statement can make nested conditional statements ambiguous. Formally, the reference context-free grammar of the language is ambiguous, meaning there is more than one correct parse tree. Description In many programming languages, one may write conditionally executed code in two forms: the if-then form, or the if-then-else form. (The else clause is optional.): if a then s if b then s1 else s2 Ambiguous interpretation becomes possible when there are nested statements; specifically when an if-then-else form replaces the statement s inside the above if-then construct: if a then if b then s1 else s2 In this example, s1 gets executed if and only if a is true ''and'' b is true. But what about s2? One person might be sure that s2 gets executed whenever a is false (by attaching the ''else'' to the first ''if''), while another person might be sure that s2 gets e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Programming
Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of procedures, by writing source code, code in one or more programming languages. Programmers typically use high-level programming languages that are more easily intelligible to humans than machine code, which is directly executed by the central processing unit. Proficient programming usually requires expertise in several different subjects, including knowledge of the Domain (software engineering), application domain, details of programming languages and generic code library (computing), libraries, specialized algorithms, and Logic#Formal logic, formal logic. Auxiliary tasks accompanying and related to programming include Requirements analysis, analyzing requirements, Software testing, testing, debugging (investigating and fixing problems), imple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eiffel (programming Language)
Eiffel is an object-oriented programming language designed by Bertrand Meyer (an object-orientation proponent and author of '' Object-Oriented Software Construction'') and Eiffel Software. Meyer conceived the language in 1985 with the goal of increasing the reliability of commercial software development. The first version was released in 1986. In 2005, the International Organization for Standardization (ISO) released a technical standard for Eiffel. The design of the language is closely connected with the Eiffel programming method. Both are based on a set of principles, including design by contract, command–query separation, the uniform-access principle, the single-choice principle, the open–closed principle, and option–operand separation. Many concepts initially introduced by Eiffel were later added into Java, C#, and other languages. New language design ideas, particularly through the Ecma/ ISO standardization process, continue to be incorporated into the Eiffe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ambiguity
Ambiguity is the type of meaning (linguistics), meaning in which a phrase, statement, or resolution is not explicitly defined, making for several interpretations; others describe it as a concept or statement that has no real reference. A common aspect of ambiguity is uncertainty. It is thus an Attribute grammar, attribute of any idea or statement whose intention, intended meaning cannot be definitively resolved, according to a rule or process with a finite number of steps. (The prefix ''wikt:ambi-#Prefix, ambi-'' reflects the idea of "2 (number), two", as in "two meanings"). The concept of ambiguity is generally contrasted with vagueness. In ambiguity, specific and distinct interpretations are permitted (although some may not be immediately obvious), whereas with vague information it is difficult to form any interpretation at the desired level of specificity. Linguistic forms Lexical ambiguity is contrasted with semantic ambiguity. The former represents a choice between a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Most Vexing Parse
The most vexing parse is a counterintuitive form of syntactic ambiguous grammar, ambiguity resolution in the C++ programming language. In certain situations, the C++ grammar cannot distinguish between the Initialization (programming), creation of an object Parameter (computer programming), parameter and Type declaration, specification of a function's type. In those situations, the compiler is required to interpret the line as the latter. Occurrence The term "most vexing parse" was first used by Scott Meyers in his 2001 book ''Effective STL''. While unusual in C (programming language), C, the phenomenon was quite common in C++ until the introduction of uniform initialization in C++11. Examples C-style casts A simple example appears when a functional cast is intended to convert an expression for initializing a variable: void f(double my_dbl) Line 2 above is ambiguous. One possible interpretation is to declare a Variable (computer science), variable i with initial value ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lexer Hack
In computer programming, the lexer hack is a solution to parsing context-sensitive grammars such as C, where classifying a sequence of characters as a variable name or a type name requires contextual information, by feeding contextual information backwards from the parser to the lexer. Lexer hack is frowned upon in modern compilers as it creates tight coupling between otherwise largely independent steps in the compilation process. Instead, identifier-like tokens are tokenized as identifiers and later disambiguated by the parser, allowing cleaner separation of concerns. Problem The fundamental problem is differentiating types from other identifiers. In the following example, the lexical class of A cannot be determined without further contextual information: A * B; This code could either be multiplication or a declaration, depending on context. In more detail, in a compiler, the lexer performs one of the earliest stages of converting the source code to a program. It scans the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Python (programming Language)
Python is a high-level programming language, high-level, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation. Python is type system#DYNAMIC, dynamically type-checked and garbage collection (computer science), garbage-collected. It supports multiple programming paradigms, including structured programming, structured (particularly procedural programming, procedural), object-oriented and functional programming. It is often described as a "batteries included" language due to its comprehensive standard library. Guido van Rossum began working on Python in the late 1980s as a successor to the ABC (programming language), ABC programming language, and he first released it in 1991 as Python 0.9.0. Python 2.0 was released in 2000. Python 3.0, released in 2008, was a major revision not completely backward-compatible with earlier versions. Python 2.7.18, released in 2020, was the last release of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rust (programming Language)
Rust is a General-purpose programming language, general-purpose programming language emphasizing Computer performance, performance, type safety, and Concurrency (computer science), concurrency. It enforces memory safety, meaning that all Reference (computer science), references point to valid memory. It does so without a conventional Garbage collection (computer science), garbage collector; instead, memory safety errors and data races are prevented by the "borrow checker", which tracks the object lifetime of references Compiler, at compile time. Rust does not enforce a programming paradigm, but was influenced by ideas from functional programming, including Immutable object, immutability, higher-order functions, algebraic data types, and pattern matching. It also supports object-oriented programming via structs, Enumerated type, enums, traits, and methods. It is popular for systems programming. Software developer Graydon Hoare created Rust as a personal project while working at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Swift (programming Language)
Swift is a High-level programming language, high-level general-purpose programming language, general-purpose, multi-paradigm programming language, multi-paradigm, compiled language, compiled programming language created by Chris Lattner in 2010 for Apple Inc. and maintained by Open-source software movement, the open-source community. Swift compiles to machine code and uses an LLVM-based compiler. Swift was first released in June 2014 and the Swift toolchain has shipped in Xcode since Xcode version 6, released in September 2014. Apple intended Swift to support many core concepts associated with Objective-C, notably dynamic dispatch, widespread late binding, extensible programming, and similar features, but in a "safer" way, making it easier to catch software bugs; Swift has features addressing some common programming errors like null pointer Dereference operator, dereferencing and provides syntactic sugar to help avoid the Pyramid of doom (programming), pyramid of doom. Swift sup ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
S-algol
S-algol (St Andrews Algol) is a computer programming language derivative of ALGOL 60 developed at the University of St Andrews in 1979 by Ron Morrison and Tony Davie. The language is a modification of ALGOL to contain orthogonal data types that Morrison created for his PhD thesis. Morrison would go on to become professor at the university and head of the department of computer science. The S-algol language was used for teaching at the university at an undergraduate level until 1999. It was also the language taught for several years in the 1980s at a local school in St. Andrews, Madras College. The computer science text ''Recursive Descent Compiling'' describes a recursive descent compiler for S-algol, implemented in S-algol. PS-algol is a persistent derivative of S-algol. It was developed around 1981 at the University of Edinburgh and of St Andrews. It supports database ability by providing for longevity of data in the form of a persistent heap that survives termination of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scheme (programming Language)
Scheme is a dialect of the Lisp family of programming languages. Scheme was created during the 1970s at the MIT Computer Science and Artificial Intelligence Laboratory (MIT CSAIL) and released by its developers, Guy L. Steele and Gerald Jay Sussman, via a series of memos now known as the Lambda Papers. It was the first dialect of Lisp to choose lexical scope and the first to require implementations to perform tail-call optimization, giving stronger support for functional programming and associated techniques such as recursive algorithms. It was also one of the first programming languages to support first-class continuations. It had a significant influence on the effort that led to the development of Common Lisp.Common LISP: The Language, 2nd Ed., Guy L. Steele Jr. Digital Press; 1981. . "Common Lisp is a new dialect of Lisp, a successor to MacLisp, influenced strongly by ZetaLisp and to some extent by Scheme and InterLisp." The Scheme language is standardized in the offic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Racket (programming Language)
Racket is a General-purpose programming language, general-purpose, multi-paradigm programming language. The Racket language is a modern dialect of Lisp (programming language), Lisp and a descendant of Scheme (programming language), Scheme. It is designed as a platform for programming language theory, programming language design and implementation. In addition to the core Racket language, ''Racket'' is also used to refer to the family of programming languages and set of tools supporting development on and with Racket. Racket is also used for script (computing), scripting, computer science education, and research. The Racket platform provides an implementation of the Racket language (including a runtime system, libraries, and compiler supporting several compilation modes: machine code, machine-independent, interpreted, and JIT) along with the DrRacket integrated development environment (IDE) written in Racket. Racket is used by the ProgramByDesign outreach program, which aims to tur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
AppleScript
AppleScript is a scripting language created by Apple Inc. that facilitates automated control of Mac applications. First introduced in System 7, it is currently included in macOS in a package of automation tools. The term ''AppleScript'' may refer to the scripting language, to a script written in the language, or to the macOS Open Scripting Architecture that underlies the language. AppleScript is primarily a mechanism for driving Apple events an inter-application communication (IAC) technology that exchanges data between and controls applications. Additionally, AppleScript supports basic calculations and text processing, and is extensible via scripting additions that add functions to the language. AppleScript is tightly bound to the Mac environment, similar to how Windows Script Host is bound to the Windows environment. In other words, AppleScript is not a general purpose scripting language like Python. One way that AppleScript is bound to the unique aspects of its env ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
