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BNF and EBNF: What are they and how do they work?What Is BNF? Backus-Naur notation (more commonly known as BNF or Backus-Naur Form) is a formal mathematical way to describe a language, which was developed by John Backus (and possibly Peter Naur as well) to describe the syntax of the Algol 60 programming language. (Legend has it that it was primarily developed by John Backus (based on earlier work by the mathematician Emil Post), but adopted and slightly improved by Peter Naur for Algol 60, which made it well-known. Because of this Naur calls BNF Backus Normal Form, while everyone else calls it Backus-Naur Form.) It is used to formally define the grammar of a language, so that there is no disagreement or ambiguity as to what is allowed and what is not. In fact, BNF is so unambiguous that there is a lot of mathematical theory around these kinds of grammars, and one can actually mechanically construct a parser for a language given a BNF grammar for it. (There are some kinds of grammars for which this isn't possible, but they can usually be transformed manually into ones that can be used.) Programs that do this are commonly called "compiler compilers". The most famous of these is YACC, but there are many more. |
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