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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.
The terminals here are a and b, while the only nonterminal is S. The language described is all nonempty strings of a {\displaystyle a} s and b {\displaystyle b} s that end in a {\displaystyle a} . This grammar is regular : no rule has more than one nonterminal in its right-hand side, and each of these nonterminals is at the same end of the ...
The right side may be the empty string, or a single terminal symbol, or a single terminal symbol followed by a nonterminal symbol, but nothing else. (Sometimes a broader definition is used: one can allow longer strings of terminals or single nonterminals without anything else, making languages easier to denote while still defining the same ...
Terminals can never appear on the left-hand side of the metasymbol ::= in a derivation rule. The body of the definition on the right-hand side may be composed with several alternative forms with each alternative syntactic construct being separated by the metasymbol |. Each of these alternative construct may be either terminal or nonterminal.
Terminal (macOS), a terminal emulator included with macOS; Windows Terminal, a terminal emulator for Windows 10 and Windows 11; GNOME Terminal, a Linux and BSD terminal emulator; Terminal and nonterminal symbols, lexical elements used in specifying the production rules constituting a formal grammar in computer science.
Let us notate a formal grammar as = (,,,), with a set of nonterminal symbols, a set of terminal symbols, a set of production rules, and the start symbol.. A string () directly yields, or directly derives to, a string (), denoted as , if v can be obtained from u by an application of some production rule in P, that is, if = and =, where () is a production rule, and , is the unaffected left and ...
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 context-sensitive grammar is a noncontracting grammar in which all rules are of the form αAβ → αγβ, where A is a nonterminal, and γ is a nonempty string of nonterminal and/or terminal symbols. However, some authors use the term context-sensitive grammar to refer to noncontracting grammars in general. [1]