BNF (Backus-Naur Form) is a metalanguage for describing the syntax of programming languages. BNF uses a set of rules to describe the grammatical structure of a language, and it consists of a set of grammatical rules, each of which is represented as a combination of a nonterminal and one or more terminals or other nonterminals.
The following is the syntax description of BNF:
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Non-terminal symbols (Non-terminal symbols): Indicates symbols in grammar rules, usually enclosed in angle brackets, eg.
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Terminal symbols: Indicates actual characters or symbols in grammar rules, such as "+", "(", ")", etc.
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Grammatical rules (Production rules): Rules representing grammatical structures composed of non-terminal symbols and terminal symbols, usually separated by arrows "->". For example:
-> +
-> *
-> ( ) |These rules describe a simple arithmetic expression language in which , , and are nonterminals, and "+", "*", "(", ")" and are terminals.
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Grammar start symbol (Start symbol): used to specify the starting point of a grammar rule, usually a non-terminal symbol. For example:
-> +
-> *
-> ( ) |In this example, is the start symbol.
The grammar description of BNF can be used to represent any form of context-free grammar. It is a general metalanguage and is widely used to define the grammar of programming languages.
How to understand context-free grammar
Context-Free Grammar (CFG) is a formal language &