Lexical Analysis

A program written in one high level language (source language) producing output in low level language (object or target language) is called compiler.

 

Cross Compiler

A compiler that runs on one machine 'A' and produces a code for another machine 'B'.

Example : (a) Compiler runs on machine A , which takes input language X and produces output language Y.

 

(b) Compiler runs on machine A and produces code Y for another machine B.

Compiler Parts 

There are two major parts of a compiler:

1. Analysis Phase : An intermediate representation is created from the given source program

      (i) Lexical Analyzer

      (ii) Syntax Analyzer

      (iii) Semantic Analyzer

2. Synthesis Phase : Equivalent target program is created from intermediate representation

       (i) Intermediate Code Generator

       (ii) Code Generator

       (iii) Code Optimizer

                                         Compiler Phases

Language Processing System

LEXICAL ANALYSIS

Lexical analyzer reads a source program character by character to produce tokens.

 

A token can represent more than one lexeme , additional information should be held for that specific lexeme.This additional information is called as attribute of the token.

Token type and its attribute uniquely identify a lexeme.

Regular expressions are used to specify patterns and finite automata is used to recognise tokens.

Token identified by lexical analyzer : Keyword , constants , identifiers , operators and symbols.

Designing of Lexical Analyzer

Write a formal description of the tokens and use a software tool that constructs table-driven lexical analyzer.

Design a state diagram that describes the tokens and write a program that implement the state diagram.

Design a state diagram that description the tokens and hand-construct a table-driven implement of the state diagram.