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parsing


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The process of deciding whether a string of input symbols is a sentence of a given language and if so determining the syntactic structure of the string as defined by a grammar (usually context-free) for the language. This is achieved by means of a program known as a parser or syntax analyzer. For example, a syntax analyzer of arithmetic expressions should report an error in the string 1-+2 since the juxtaposition of the minus and plus operators is invalid. On the other hand the string 1-2-3 is a valid arithmetic expression with structure specified by the statement that its subexpressions are 1,2,3 and 1-2 (Note that 2‒3 is not a subexpression.)

1-+2

1-2-3

1,2,3 and 1-2

The input to a parser is a string of tokens supplied by a lexical analyzer. Its output may be in the form of a parse tree or a derivation sequence. See also bottom-up parsing, top-down parsing, precedence parsing.

Subjects: Computing — Linguistics.


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