Apply Event$-$Driven Techniques to an Input Stream.

Use FSAs $(\backslash$epsi $-$NFAs, NFAs and$/$or DFAs$)$ to evaluate the inputs against for a given Regular Expression.

$2.$ writing code to simulate a FSA based regular expression engine.

The system you develop will need to generate the FSA structures that match a given Regex dynamically and then evaluate several series' of inputs against that FSA to determine whether they are a match.

This assignment requires you to apply concepts and techniques covered in Chapters $0-4$ of the Notes on FSAs $($see course readings$).$

You'll also need to document and thoroughly test your code using unit tests to ensure robust event handling techniques are being used.

$3.$ The system will need to:

Parse an basic regular expression from standard input

Generate a $\backslash$epsi $-$NFA to evaluate the regular expression

Evaluate the subsequent inputs against the regular expression.

Event Driven systems are particularly prone to errors so you'll also need to:

Document your planning of the system $($See Logging$/$Documenting your Progress below$)$

Write your own suite of test cases for your code $($See Testing your Code below$)$

ONLY USE THIS IF YOU KNOW WHAT YOU ARE DOING:

apt $-$y install openjdk$-11-$jdk junit$4$

Your implementation must not use any of the programming language's inbuilt regular expression parsing$/$evaluation libraries$/$classes$.$

Your implementation may use any other libraries$/$classes available in the standard JDK and JUnit, but no other external libraries$/$classes$.$

Your programs will be executed with the commands shown below:

Compiled with

javac RegexEngine.java

Run with:

java RegexEngine

or for verbose mode

java RegexEngine $-$v

Tests compiled with:

javac $*\_$Test.java

Each Test run with:

java org.junit.runner.JUnitCore TestName$\_$Test

Your program will need to read input from the terminal$/$command line's standard input $($System$.$in$).$

The expected input format is as follows:

$($ab$)*|$c$+$

abc

ccc

The input begins with the regular expression to test.

In this assignment, a regular expression can consist of lower and upper case letters, numbers, spaces, the alternation operator $(|),$ the Kleene star and Kleene plus operators $(*$ and $+),$ as well as brackets $(($ and $)).$

You are not expected to handle nested brackets.

Invalid input in this section should cause the program to print an error message and exit with an exit code of $1.$

The next section of input contains the input strings to evaluate against the regular expression.

Each string is on its own line; when a new line is entered, another string begins $($don$\text{'}$t forget to reset states$)$

A string can be empty$/$blank$.$

A string can contain whitespace and other control characters.

This repeats until the program is terminated with a SIGTERM $($Ctrl$-$C$).$The program has $2$ output modes; a normal mode and verbose mode.

Verbose should trigger if the user adds a $-$v when running the program $($see Software Requirements above$)$

Under normal mode

After the user has entered the regex your program should print ready

Your program should then print true or false once for each input string provided as they are entered.

If the input string matches the regular expression, print true

If the input string does not match, print false

The input string should be evaluated for an exact match

i$.$e$.$ the whole string from start to end must exactly match the regular expression to be accepted.

A string containing a match, but not exactly matching should print false.

Example $($user input is grey, output is highlighted pink$)$

$($ab$)*|$c$+$

ready

abc

false

ccc

true

Under verbose mode

After the user has entered the regex your program should print a transition table for the $-$NFA generated followed by the word ready

The transition table does not have to exactly match the example below, but does need to reflect the $-$NFA generated by your system;

this is for manual review and your own debugging.

Your program should begin to print true or false as the user enters the input strings for each character input $($including the initial state$),$

If the system is currently in an accepting state, print true

Otherwise, print false

Hint: After a user has entered the input string the most recent output should match the normal output

Example $($user input is grey, output is highlighted pink$)$

$($ab$)*|$c$+$

epsilon a b c other

$>$q$0$ q$1,$q$5$

q$1$ q$2,$q$8$

q$2$ q$3$

q$3$ q$4$

q$4$ q$1$

q$5$ q$6$

q$6$ q$7$

q$7$ q$5,$q$8$

$*$q$8$

ready

true

a

false

b

true

c

false

true

c

true

c

true

c

true