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Lexical and Syntax Analysis

Lexical and Syntax Analysis. David Woolbright. Syntax Analysers or Parsers. Usually based on a formal description of a language Context-free grammars or BNF are used to describe the syntax of a language Parsers are organized into two parts

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Lexical and Syntax Analysis

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  1. Lexical and Syntax Analysis David Woolbright

  2. Syntax Analysers or Parsers • Usually based on a formal description of a language • Context-free grammars or BNF are used to describe the syntax of a language • Parsers are organized into two parts • Lexical analyser – small scale language constructs – names, literals • Syntax analyser – large scale language constructs – expressions, statements, …

  3. Why Separate? • Simplicity – lexical analysis is easier than syntax analysis • Efficiency – lexical analysis can be optimized • Portability – lexical analysis is platform dependent

  4. Lexical Analysis • Pattern matching • Languages described by DFA • Easily translated • Acts as a front end for syntactic analysis • Collects characters and outputs lexemes (character groupings). • Internal codes are called tokens

  5. Lexical Analysis • Produces the “next” lexeme and token • Skips comments and white space • Inserts user-defined names into a symbol table (for later use by a compiler) • Detect syntactic errors in tokens

  6. Building a Lexical Analyser • Write a formal description of the token patterns using a descriptive language related to regular expressions. Use a software tool to generate the lexical analyser • Design a DFA for the token patterns and write a program that implements the DFA • Design a DFA for the token patterns and hand-construct a table driven implementation of the DFA

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