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Terminal symbols are the elementary symbols of the language defined as part of a formal grammar. Nonterminal symbols (or syntactic variables) are replaced by groups of terminal symbols according to the production rules. The terminals and nonterminals of a particular grammar are in two completely separate sets.
In this variant, each production for a given non-terminal is given a label, which can be used as a constructor of an algebraic data type representing that nonterminal. The converter is capable of producing types and parsers for abstract syntax in several languages, including Haskell and Java
Each variable represents a different type of phrase or clause in the sentence. Variables are also sometimes called syntactic categories. Each variable defines a sub-language of the language defined by G. Σ is a finite set of terminals, disjoint from V, which make up the actual content of the sentence
In C and Java, syntactic categories are denoted using italic font while terminal symbols are denoted by gothic font. In J , its metasyntax does not apply metasymbols to describe J's syntax at all. Rather, all syntactic explanations are done in a metalanguage very similar to English called Dictionary, which is uniquely documented for J.
The vertical bar represents an alternative and the terminal symbols are enclosed with quotation marks followed by a semicolon as terminating character. Hence a digit is a 0 or a digit excluding zero that can be 1 or 2 or 3 and so forth until 9. A production rule can also include a sequence of terminals or nonterminals, each separated by a comma:
[3] [4] [5] The rules are absolute and have a typical syntax representation known as Backus–Naur form. The production rules consist of terminal {,} and non-terminal S symbols and a blank may also be used as an end point. In the production rules of CFG and PCFG the left side has only one nonterminal whereas the right side can be any string of ...
where A, B, and C are nonterminal symbols, the letter a is a terminal symbol (a symbol that represents a constant value), S is the start symbol, and ε denotes the empty string. Also, neither B nor C may be the start symbol , and the third production rule can only appear if ε is in L ( G ), the language produced by the context-free grammar G .
A → w, where A is a non-terminal in N and w is in a (possibly empty) string of terminals Σ * A → wB, where A and B are in N and w is in Σ *. Some authors call this type of grammar a right-regular grammar (or right-linear grammar) [1] and the type above a strictly right-regular grammar (or strictly right-linear grammar). [2]