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Applying the rules recursively to a source string of symbols will usually terminate in a final output string consisting only of terminal symbols. Consider a grammar defined by two rules. In this grammar, the symbol Б is a terminal symbol and Ψ is both a non-terminal symbol and the start symbol. The production rules for creating strings are as ...
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
An unrestricted grammar is a formal grammar = (,,,), where . is a finite set of nonterminal symbols,; is a finite set of terminal symbols with and disjoint, [note 1]; is a finite set of production rules of the form , where and are strings of symbols in and is not the empty string, and
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]
An EBNF consists of terminal symbols and non-terminal production rules which are the restrictions governing how terminal symbols can be combined into a valid sequence. Examples of terminal symbols include alphanumeric characters , punctuation marks , and whitespace characters .
A nondeterministic programming language is a language which can specify, at certain points in the program (called "choice points"), various alternatives for program flow. Unlike an if-then statement , the method of choice between these alternatives is not directly specified by the programmer; the program must decide at run time between the ...
A starting non-terminal produces loops. The rest of the grammar proceeds with parameter L {\displaystyle \mathbf {\mathit {L}} } that decide whether a loop is a start of a stem or a single stranded region s and parameter F {\displaystyle \mathbf {\mathit {F}} } that produces paired bases.
This recursive definition is an example of a meta-language. [98] The syntax of BNF includes: ::= which translates to is made up of a[n] when a non-terminal is to its right. It translates to is when a terminal is to its right. | which translates to or. < and > which surround non-terminals.