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Python has two major implementations, the built in re and the regex library. Ruby 1.8, Ruby 1.9, and Ruby 2.0 and later versions use different engines; Ruby 1.9 integrates Oniguruma, Ruby 2.0 and later integrate Onigmo, a fork from Oniguruma. The primary regex crate does not allow look-around expressions.
A regular expression (shortened as regex or regexp), [1] sometimes referred to as rational expression, [2][3] is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation.
To do so technically would require a more sophisticated grammar, like a Chomsky Type 1 grammar, also termed a context-sensitive grammar. However, parser generators for context-free grammars often support the ability for user-written code to introduce limited amounts of context-sensitivity. (For example, upon encountering a variable declaration ...
Website. pcre.org. Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [3] PCRE's syntax is much more powerful and flexible than either of the POSIX regular expression ...
Thompson's construction. In computer science, Thompson's construction algorithm, also called the McNaughton–Yamada–Thompson algorithm, [1] is a method of transforming a regular expression into an equivalent nondeterministic finite automaton (NFA). [2] This NFA can be used to match strings against the regular expression.
The Boyer–Moore algorithm uses information gathered during the preprocess step to skip sections of the text, resulting in a lower constant factor than many other string search algorithms. In general, the algorithm runs faster as the pattern length increases. The key features of the algorithm are to match on the tail of the pattern rather than ...
RE/flex. RE/flex (regex-centric, fast lexical analyzer) [1][2] is a free and open source computer program written in C++ that generates fast lexical analyzers (also known as "scanners" or "lexers") [3][4] in C++. RE/flex offers full Unicode support, indentation anchors, word boundaries, lazy quantifiers (non-greedy, lazy repeats), and ...
In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance. It is one of the well-known "Gang of Four" design patterns, which describe how to solve recurring problems in object-oriented software. [1] The pattern is useful when exactly one object is needed ...