Compiler

Lexical Analysis

  if (i == j)
    z = 0;
  else
    z = 1;

is indeed below in computers

\tif (i == j)\n\t\tz = 0;\n\telse\n\t\tz = 1;

An implementation must do

1. Recognize substrings corresponding to tokens
2. Identify the token class of each lexeme

Token Class

Identifier, keywords, '(', ')', Numbers, ...

• Token classes correspond to sets of strings.
• Identifier: A1, Foo, B17
• Integer: 0, 99
• Keyword: 'else' or 'if' or 'begin' or ...
• Whitespace: if___else

For the last code example, the tokens are: if, whitespace, (, i, == , j, \t, \n, else, z, =, 1, ;

                                 Token    
   string ---> Lexical Analysis -------> Parser

Regular Languages

Regular expressions specify regular languages.

Five constructs

• Two base cases - empty and 1-character strings
• Three compound expressions - union, concatenation, iteration.

Finite Automata

• Regular expressions = specification
• Finite automata = implementation

A finite automaton consists of

• input alphabet
• set of states
• start state
• set of accepting states
• set of transitions

Resource

• coursera.org