creating a lexical analyzer with LEX, Lexical analyzer, LEX compiler, NFA construction using LEX

1. Lexical Analysis

3. Lexical Analysis With Lex

4. Lexical analysis with Lex

5. Lex source program format
• The Lex program has three sections, separated
by %%:
declarations
%%
transition rules
%%
auxiliary code

6. Declarations section
• Code between %{ and }% is inserted directly into the lex.yy.c. Should
contain:
– Manifest constants (#define for each token)
– Global variables, function declarations, typedefs
• Outside %{ and }%, REGULAR DEFINITIONS are declared.
Examples:
delim [ tn]
ws {delim}+
letter [A-Za-z]
Each definition is a name
followed by a pattern.
Declared names can be used in
later patterns, if surrounded by
{ }.

7. Translation rules section
Translation rules take the form
p1 { action1 }
p2 { action2 }
… …
pn { actionn }
Where pi is a regular expression and actioni is a C program fragment to be
executed whenever pi is recognized in the input stream.
In regular expressions, references to regular definitions must be enclosed in
{} to distinguish them from the corresponding character sequences.