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The 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] |
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] |
Hack (computer Science)
A kludge or kluge () is a workaround or makeshift solution that is clumsy, inelegant, inefficient, difficult to extend, and hard to maintain. This term is used in diverse fields such as computer science, aerospace engineering, Internet slang, evolutionary neuroscience, animation and government. It is similar in meaning to the naval term ''jury rig''. Etymology The word has alternate spellings (''Wikt:kludge, kludge'' and ''Wikt:kluge, kluge''), pronunciations ( and , rhyming with ''judge'' and ''stooge'', respectively), and several proposed etymologies. Jackson W. Granholm The ''Oxford English Dictionary'' (2nd ed., 1989), cites Jackson W. Granholm's 1962 "How to Design a Kludge" article in the American computer magazine ''Datamation''. ''OED'' defines these two ''kludge'' Cognate (etymology), cognates as: ''bodge'' 'to patch or mend clumsily' and ''fudge'' 'to fit together or adjust in a clumsy, makeshift, or dishonest manner'. The ''OED'' entry also includes the verb ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C (programming Language)
C (''pronounced'' '' – like the letter c'') is a general-purpose programming language. It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted Central processing unit, CPUs. It has found lasting use in operating systems code (especially in Kernel (operating system), kernels), device drivers, and protocol stacks, but its use in application software has been decreasing. C is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems. A successor to the programming language B (programming language), B, C was originally developed at Bell Labs by Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. It has become one of the most widely used programming langu ... [...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] |
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] |
Semantic Analysis (compilers)
Semantic analysis or context sensitive analysis is a process in compiler construction, usually after parsing, to gather necessary semantic information from the source code. It usually includes type checking, or makes sure a variable is declared before use which is impossible to describe in the extended Backus–Naur form Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (proof theory) * Extension (predicate logic), the set of tuples of values ... and thus not easily detected during parsing. See also * Attribute grammar * Context-sensitive language * Semantic analysis (computer science) References Compiler construction Program analysis {{plt-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clang
Clang () is a compiler front end for the programming languages C, C++, Objective-C, Objective-C++, and the software frameworks OpenMP, OpenCL, RenderScript, CUDA, SYCL, and HIP. It acts as a drop-in replacement for the GNU Compiler Collection (GCC), supporting most of its compiling flags and unofficial language extensions. It includes a static analyzer, and several code analysis tools. Clang operates in tandem with the LLVM compiler back end and has been a subproject of LLVM 2.6 and later. As with LLVM, it is free and open-source software under the Apache 2.0 software license. Its contributors include Apple, Microsoft, Google, ARM, Sony, Intel, and AMD. Clang 17, the latest major version of Clang as of October 2023, has full support for all published C++ standards up to C++17, implements most features of C++20, and has initial support for the C++23 standard. Since v16.0.0, Clang compiles C++ using the GNU++17 dialect by default, which includes features fro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Berkeley Yacc
Berkeley Yacc (byacc) is a Unix parser generator designed to be compatible with Yacc. It was originally written by Robert Corbett and released in 1989. Due to its liberal license and because it was faster than the AT&T Yacc, it quickly became the most popular version of Yacc. It has the advantages of being written in ANSI C89 and being public domain software. It contains features not available in Yacc, such as reentrancy, which is implemented in a way that is broadly compatible with GNU Bison. History In 1985, Robert Corbett developed an original LALR parser generator based on a 1982 paper by DeRemer and Pennello. Corbett wrote it as part of his research towards the Ph.D. he received from University of California, Berkeley in June 1985. It was originally named Byson and was incompatible with Yacc but it was subsequently renamed Bison and became the basis of GNU Bison. Later in 1985, Corbett developed his LALR parser generator, making it Yacc-compatible and naming it Zeus but s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concurrent Computation
Concurrent computing is a form of computing in which several computations are executed ''Concurrency (computer science), concurrently''—during overlapping time periods—instead of ''sequentially—''with one completing before the next starts. This is a property of a system—whether a computer program, program, computer, or a computer network, network—where there is a separate execution point or "thread of control" for each process. A ''concurrent system'' is one where a computation can advance without waiting for all other computations to complete. Concurrent computing is a form of modular programming. In its programming paradigm, paradigm an overall computation is decomposition (computer science), factored into subcomputations that may be executed concurrently. Pioneers in the field of concurrent computing include Edsger Dijkstra, Per Brinch Hansen, and C.A.R. Hoare. Introduction The concept of concurrent computing is frequently confused with the related but distinct c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lexerless Parsing
In computer science, scannerless parsing (also called lexerless parsing) performs tokenization (breaking a stream of characters into words) and parsing (arranging the words into phrases) in a single step, rather than breaking it up into a pipeline of a lexer followed by a parser, executing concurrently. A language grammar is scannerless if it uses a single formalism to express both the lexical (word level) and phrase level structure of the language. Dividing processing into a lexer followed by a parser is more modular; scannerless parsing is primarily used when a clear lexer–parser distinction is unneeded or unwanted. Examples of when this is appropriate include TeX, most wiki grammars, makefiles, simple application-specific scripting languages, and Raku. Advantages * Only one metalanguage is needed * Non-regular lexical structure is handled easily * "Token classification" is unneeded which removes the need for design accommodations such as "the lexer hack" and language re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pipeline (software)
In software engineering, a pipeline consists of a chain of processing elements ( processes, threads, coroutines, functions, ''etc.''), arranged so that the output of each element is the input of the next. The concept is analogous to a physical pipeline. Usually some amount of buffering is provided between consecutive elements. The information that flows in these pipelines is often a stream of records, bytes, or bits, and the elements of a pipeline may be called filters. This is also called the pipe(s) and filters design pattern which is monolithic. Its advantages are simplicity and low cost while its disadvantages are lack of elasticity, fault tolerance and scalability. Connecting elements into a pipeline is analogous to function composition. Narrowly speaking, a pipeline is linear and one-directional, though sometimes the term is applied to more general flows. For example, a primarily one-directional pipeline may have some communication in the other direction, known as a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parsing
Parsing, syntax analysis, or syntactic analysis is a process of analyzing a String (computer science), string of Symbol (formal), symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal grammar by breaking it into parts. The term ''parsing'' comes from Latin ''pars'' (''orationis''), meaning Part of speech, part (of speech). The term has slightly different meanings in different branches of linguistics and computer science. Traditional Sentence (linguistics), sentence parsing is often performed as a method of understanding the exact meaning of a sentence or word, sometimes with the aid of devices such as sentence diagrams. It usually emphasizes the importance of grammatical divisions such as subject (grammar), subject and predicate (grammar), predicate. Within computational linguistics the term is used to refer to the formal analysis by a computer of a sentence or other string of words into its constituents, resulting in a par ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
