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How did Backus-Naur Form help describe the grammar of programming languages?

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Developed by John Backus and Peter Naur for the ALGOL 60 programming language, Backus-Naur Form (BNF) provided a formal, standardized notation for describing the syntax—or grammar—of programming languages.123

Before its introduction, there was no consistent method for defining the structural rules of a language. BNF helped solve this by providing a clear, mathematical way to define the valid sequences of symbols and structures that constitute a program. By establishing a rigorous framework for syntax, it allowed computer scientists to precisely specify how language components, such as expressions and statements, should be constructed.23

This innovation became a standard tool in computer science, enabling the development of more complex and reliable languages. Many influential programming languages, including Pascal and C, were built upon the foundations established by the grammar defined in BNF.23