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In computer science, extended Backus–Naur form (EBNF) is a family of metasyntax notations, any of which can be used to express a context-free grammar.EBNF is used to make a formal description of a formal language such as a computer programming language.
Declarative programming may greatly simplify writing parallel programs. [5] 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.
Python sets are very much like mathematical sets, and support operations like set intersection and union. Python also features a frozenset class for immutable sets, see Collection types. Dictionaries (class dict) are mutable mappings tying keys and corresponding values. Python has special syntax to create dictionaries ({key: value})
DECLARE ARRAY S; function INIT (words) S ← CREATE_ARRAY (LENGTH (words) + 1) for k ← from 0 to LENGTH (words) do S [k] ← EMPTY_ORDERED_SET function EARLEY_PARSE (words, grammar) INIT (words) ADD_TO_SET ((γ → • S, 0), S [0]) for k ← from 0 to LENGTH (words) do for each state in S [k] do // S[k] can expand during this loop if not FINISHED (state) then if NEXT_ELEMENT_OF (state) is a ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 2 January 2025. Language for communicating instructions to a machine The source code for a computer program in C. The gray lines are comments that explain the program to humans. When compiled and run, it will give the output "Hello, world!". A programming language is a system of notation for writing ...
Figure 1. Finding the shortest path in a graph using optimal substructure; a straight line indicates a single edge; a wavy line indicates a shortest path between the two vertices it connects (among other paths, not shown, sharing the same two vertices); the bold line is the overall shortest path from start to goal.
The specification of a programming language often includes a set of rules, the lexical grammar, which defines the lexical syntax. The lexical syntax is usually a regular language, with the grammar rules consisting of regular expressions; they define the set of possible character sequences (lexemes) of a token. A lexer recognizes strings, and ...
A weighted context-free grammar (WCFG) is a more general category of context-free grammar, where each production has a numeric weight associated with it. The weight of a specific parse tree in a WCFG is the product [7] (or sum [8]) of all rule weights in the tree. Each rule weight is included as often as the rule is used in the tree.