Community hub
Recent from talks
Knowledge base stats:
Talk channels stats:
Members stats:
Backus–Naur form
In computer science, Backus–Naur form or Pāṇini–Backus Form (BNF or PBF, pronounced /ˌbækəs ˈnaʊər/), also known as Backus normal form, is a notation system for defining the syntax of programming languages and other formal languages, developed by John Backus and Peter Naur. It is a metasyntax for context-free grammars, providing a precise way to outline the rules of a language's structure.
It has been widely used in official specifications, manuals, and textbooks on programming language theory, as well as to describe document formats, instruction sets, and communication protocols. Over time, variations such as extended Backus–Naur form (EBNF) and augmented Backus–Naur form (ABNF) have emerged, building on the original framework with added features.
BNF specifications outline how symbols are combined to form syntactically valid sequences. Each BNF consists of three core components: a set of non-terminal symbols, a set of terminal symbols, and a series of derivation rules. Non-terminal symbols represent categories or variables that can be replaced, while terminal symbols are the fixed, literal elements (such as keywords or punctuation) that appear in the final sequence. Derivation rules provide the instructions for replacing non-terminal symbols with specific combinations of symbols.
A derivation rule is written in the format: <symbol> ::= __expression__
where:
For example, in the rule <opt-suffix-part> ::= "Sr." | "Jr." | "", the entire line is the derivation rule, "Sr.", "Jr.", and "" (an empty string) are terminal symbols, and <opt-suffix-part> is a non-terminal symbol.
Generating a valid sequence involves starting with a designated start symbol and iteratively applying the derivation rules. This process can extend sequences incrementally. To allow flexibility, some BNF definitions include an optional "delete" symbol (represented as an empty alternative, e.g., <item> ::= <thing> | ), enabling the removal of certain elements while maintaining syntactic validity.
A practical illustration of BNF is a specification for a simplified U.S. postal address:
Hub AI
Backus–Naur form AI simulator
(@Backus–Naur form_simulator)
Backus–Naur form
In computer science, Backus–Naur form or Pāṇini–Backus Form (BNF or PBF, pronounced /ˌbækəs ˈnaʊər/), also known as Backus normal form, is a notation system for defining the syntax of programming languages and other formal languages, developed by John Backus and Peter Naur. It is a metasyntax for context-free grammars, providing a precise way to outline the rules of a language's structure.
It has been widely used in official specifications, manuals, and textbooks on programming language theory, as well as to describe document formats, instruction sets, and communication protocols. Over time, variations such as extended Backus–Naur form (EBNF) and augmented Backus–Naur form (ABNF) have emerged, building on the original framework with added features.
BNF specifications outline how symbols are combined to form syntactically valid sequences. Each BNF consists of three core components: a set of non-terminal symbols, a set of terminal symbols, and a series of derivation rules. Non-terminal symbols represent categories or variables that can be replaced, while terminal symbols are the fixed, literal elements (such as keywords or punctuation) that appear in the final sequence. Derivation rules provide the instructions for replacing non-terminal symbols with specific combinations of symbols.
A derivation rule is written in the format: <symbol> ::= __expression__
where:
For example, in the rule <opt-suffix-part> ::= "Sr." | "Jr." | "", the entire line is the derivation rule, "Sr.", "Jr.", and "" (an empty string) are terminal symbols, and <opt-suffix-part> is a non-terminal symbol.
Generating a valid sequence involves starting with a designated start symbol and iteratively applying the derivation rules. This process can extend sequences incrementally. To allow flexibility, some BNF definitions include an optional "delete" symbol (represented as an empty alternative, e.g., <item> ::= <thing> | ), enabling the removal of certain elements while maintaining syntactic validity.
A practical illustration of BNF is a specification for a simplified U.S. postal address: