Merge: contrib/re_parser

Merge: contrib/re_parser

# RE Parser

RE parser provides a simple API to regular expression parsing.
It is also able to convert a regular expression into a NFA or a DFA and produce dot files from it.

## Building RE parser

From the `re_parser` directory:

~~~bash
make all
~~~

## RE parser in command line

RE parser can be used as a command line tool to generate NFA and DFA dot files from a regular expression:

~~~bash
./re_parser "a(b|c)+d*"
~~~

Will produce the two files `nfa.dot` and `dfa.dot`.

These can be directly viwed with `xdot`:

~~~bash
xdot nfa.dot
xdot dfa.dot
~~~

Or translated to png images with `dot`:

~~~bash
dot -Tpng -onfa.png nfa.dot
dot -Tpng -odfa.png dfa.dot
~~~

See `man dot` for available formats.

## RE parser as a web app

RE parser comes with a web app that allow users to submit regular expression and see the resulting NFA and DFA.

To run the web app server:

~~~bash
./re_app --host localhost --port 3000
~~~

The server will be available at <a href='http://localhost:3000'>http://localhost:3000</a>.

## RE parser as a library

You can also use RE parser as a library by importing `re_parser`.

~~~nit
	import re_parser

	var re = "a(b|c)+d*"

	# Parse the expression
	var l = new Lexer_re_parser(re)
	var p = new Parser_re_parser
	p.tokens.add_all l.lex
	var node = p.parse

	# Check errors
	if not node isa NProd then
		print "Error parsing the regular expression"
		abort
	end

	# Get NFA and DFA
	var v = new REVisitor
	v.start(node)
	print v.nfa.to_dot
	print v.nfa.to_dfa.to_dot
~~~

Web app demo: http://re.moz-code.org/

Pull-Request: #2373
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Jean-Christophe Beaupré <jcbrinfo.public@gmail.com>