Search results
Results from the WOW.Com Content Network
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 ...
A derivation rule is composed by a nonterminal symbol and an expression . A special expression α s {\displaystyle \alpha _{s}} is the starting point of the grammar. [ 2 ] In case no α s {\displaystyle \alpha _{s}} is specified, the first expression of the first rule is used.
Metalanguages have their own metasyntax each composed of terminal symbols, nonterminal symbols, and metasymbols. A terminal symbol, such as a word or a token, is a stand-alone structure in a language being defined. A nonterminal symbol represents a syntactic category, which defines one or more valid phrasal or sentence structure consisted of an ...
The algorithm works by scanning a sequence of terminal symbols and building a list of all the symbol pairs which it has read. Whenever a second occurrence of a pair is discovered, the two occurrences are replaced in the sequence by an invented nonterminal symbol, the list of symbol pairs is adjusted to match the new sequence, and scanning ...
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.
Nonterminal symbols are blue and terminal symbols are red. In formal language theory, a context-free grammar (CFG) is a formal grammar whose production rules can be applied to a nonterminal symbol regardless of its context. In particular, in a context-free grammar, each production rule is of the form
::= means that the symbol on the left must be replaced with the expression on the right. __expression__ consists of one or more sequences of either terminal or nonterminal symbols where each sequence is separated by a vertical bar "|" indicating a choice, the whole being a possible substitution for the symbol on the left.
As can be seen from the example, the parser performs three types of steps depending on whether the top of the stack is a nonterminal, a terminal or the special symbol $: If the top is a nonterminal then the parser looks up in the parsing table, on the basis of this nonterminal and the symbol on the input stream, which rule of the grammar it ...