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[citation needed] Note that the constant is independent of the length of the token, the length of the regular expression and the size of the DFA. However, using the REJECT macro in a scanner with the potential to match extremely long tokens can cause Flex to generate a scanner with non-linear performance. This feature is optional.
JavaCC (Java Compiler Compiler) is an open-source parser generator and lexical analyzer generator written in the Java programming language. [ 2 ] JavaCC is similar to yacc in that it generates a parser from a formal grammar written in EBNF notation.
Input position 0 is the position prior to input. Input position n is the position after accepting the nth token. (Informally, input positions can be thought of as locations at token boundaries.) For every input position, the parser generates a state set. Each state is a tuple (X → α • β, i), consisting of
A lexical token is a string with an assigned and thus identified meaning, in contrast to the probabilistic token used in large language models. A lexical token consists of a token name and an optional token value. The token name is a category of a rule-based lexical unit. [2]
Much of the LR parser's efficiency is from being deterministic. To avoid guessing, the LR parser often looks ahead (rightwards) at the next scanned symbol, before deciding what to do with previously scanned symbols. The lexical scanner works one or more symbols ahead of the parser.
In a language such as C, "int *ptr" denotes the definition of a pointer, not a product: it would be wrong to name this "*" "TOKEN_MULTIPLY". Since the tokens are provided by flex we must provide the means to communicate between the parser and the lexer. [23] The data type used for communication, YYSTYPE, is set using Bison %union declaration.
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This is the first stage where the scanner will read the input source files to identify all static and extern usages. Each line in the file will be checked against pre-defined patterns to segregate into tokens. These tokens will be stored in a file which will be used later by the grammar engine.