[PDF] application of regular expression in lexical analysis

The lexical analyzer needs to scan and identify only a finite set of valid string/token/lexeme that belong to the language in hand. It searches for the pattern defined by the language rules. Regular expressions have the capability to express finite languages by defining a pattern for finite strings of symbols.
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  • What are the applications of regular expressions?

    A scanner or lexical analyzer for the language uses a DFA (recognizer of regular languages) in its core. Different final states of the DFA identifies different tokens.
    Synthesis of this DFA from the set of regular expressions can be automated.

  • What is the role of regular expression and DFA in lexical analyzer?

    Finite automata is a state machine that takes a string of symbols as input and changes its state accordingly. Finite automata is a recognizer for regular expressions.
    When a regular expression string is fed into finite automata, it changes its state for each literal.

  • What are the role of finite automata and regular expression in the lexical analysis phase?

    Regular expression is an important notation for specifying patterns.
    Each pattern matches a set of strings, so regular expressions serve as names for a set of strings.
    Programming language tokens can be described by regular languages.

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