EBNF is a notation for formally describing syntax: how to write the linguistic We will use EBNF to This book uses Extended Backus–Naur Form (EBNF) to. Nonterminals written as-is. – Special symbols (partial list). Note: this is only one variation of EBNF syntax, there are other variations as well. Symbol. Meaning.. How did BNF come about? • John Backus presented a new notation containing most of the elements of BNF at a UNESCO conference. • His presentation was.

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The enf way to manage precedence is to define a list of different rules that refers to each other. I’ll discuss grammars beyond context-free at the end.

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EBNF: How to Describe the Grammar of a Language

The name of a class of literals is usually defined by other means, such as a regular expression or even prose.

In languages like Haskell, identifiers used for types must start with an uppercase letter. Based on this, we could: Some of them can contain other statements. We have seen that non-terminals represent structures at different levels. As an aside, if you think you’ve invented a new parsing technique, you need to check this book first. To go beyond the expressive power of context-free grammars, one needs to allow tugorial degree of context-sensitivity in the grammar.


After reading this article, you will be able to identify and interpret all commonly used notation for grammars. Left recurring grammars are more common. Context-free grammars have sufficient richness to describe the recursive syntactic structure of many though certainly not tutirial languages. An EBNF grammar is useful to support discussion and to communicate with other langue designers.

Okay, but what does EBNF stand for? In the grammar, we will define the parser rules that determine how the AST is built. A name referring to a terminal definition. Grouping We can group multiple elements together by using round parenthesis. Not all of these are strictly a superset, as some change the rule-definition relation:: There are some constructs, or portions of constructs, that can be defined in different ways.

Grammar: The language of languages (BNF, EBNF, ABNF and more)

Regular expressions sit just beneath context-free grammars in descriptive power: This is not the case for all the languages. In the rest of the article, we will add more comments when looking at specific parts of EBNF. How to Describe the Grammar of a Language. By combining syntactic and semantic rules we can express what is valid in our language.


We could have just one, or more program: However, ebhf can lead to left-recursive rules that are typically forbidden. A terminal tuyorial be either: Some languages could have more structured forms of documentation comments.

For more details see the paragraph on recursion in grammars. Sign up for free now. We can have string literals, numeric literal, char literals, boolean literals but we could consider them keywords as wellarray literals, map ebnd, and more, depending on the language.

Terminal We have seen that a terminal can be defined in-line, specifying a string or a regular expression, or can be defined elsewhere and simply referred to in a rule. Your peer reviewers will check it.

BNF and EBNF: What are they and how do they work?

So, if ebnnf can, just use modern tooling that deals with left and right recurring grammars. Later, we could refer to them while explaining the rules.

What does it mean?