ANN: Regexador - A mini-language for regular expressions

Ruby
1

This is a new project, but is reasonably mature for its age. :wink:

See GitHub - Hal9000/regexador: An external DSL for Ruby that tries to make regular expressions readable and maintainable.

When a regular expression grows too complex to read or maintain,
construct a small script to describe it instead.

Example from the README (see below).

Comments welcome.

Thanks!
Hal F.

Suppose we want to match a string consisting of a single IP address.
(Remember that the numbers can only range as high as 255.)

Here is traditional regular expression notation:

/^(25[0-5]|2[0-4]\d|([01])?(\d){1,2}).(25[0-5]|2[0-4]\d|([01])?(\d){1,2}).(25[0-5]|2[0-4]\d|([01])?(\d){1,2}).(25[0-5]|2[0-4]\d|([01])?(\d){1,2})$/

And here is Regexador notation:

dot = "."
num = "25" D5 | `2 D4 D | maybe D1 1,2*D
match BOS num dot num dot num dot num EOS end

In your Ruby code, you can create a Regexador “script” or “program”
(probably by means of a here-document) that you can then pass into
the Regexador class. At minimum, you can convert this into a “real”
Ruby regular expression; there are a few other features and functions,
and more may be added.

So here is a complete Ruby program:

require 'regexador'

program = <<-EOS
  dot = "."
  num = "25" D5 | `2 D4 D | maybe D1 0,2*D
  match WB num dot num dot num dot num WB end
EOS

pattern = Regexador.new(program)

puts "Give me an IP address"
str = gets.chomp

rx = pattern.to_regex    # Can retrieve the actual regex

if pattern.match?(str)   # ...or use in other direct ways
  puts "Valid"
else
  puts "Invalid"
end
2

From the README:

“I’m thinking of ignoring these features for now:
Unicode chars”
And out. This is not a serious endeavour.

Am 07.09.2013 um 00:50 schrieb Hal F. [email protected]:

3

On 2013-09-06, at 11:50 PM, Hal F. [email protected] wrote:

and more may be added.

  puts "Invalid"
end

This looks like a fun project which Ill look into.

I think youve made regexes look worse than they need to (though that
might well be how a person unfamiliar with regexes actually uses them).
The comments below are about regexes rather than your project.

I think it is possible to achieve a lot with interpolation in Rubys
regular expressions, remembering that \A and \z are the real end of
string anchors, and using the x modifier.

#!/usr/bin/env ruby

BYTE = / (?:
25[0-5] | # 250 … 255
2[0-4]\d | # 200 … 249
[01]?\d{1,2} # 0 … 199
)
/x

IP_ADDR4 = / \A #{BYTE} . #{BYTE} . #{BYTE} . #{BYTE} \z /x

p IP_ADDR4

print "Give me an address: "
if IP_ADDR4 =~ gets.chomp
puts “Good”
else
puts “Bad”
end

END

Of course my Perl history makes the regex version seem clear to me.

I would usually decompose the text using a regular expression and then
do the validation using code, for example something like:

def ipv4_address?(string)
md = /\A (\d{1,3}) . (\d{1,3}) . (\d{1,3}) . (\d{1,3}) \z/x.match
string
md && md.captures.all? { |num| num.to_i.between?(0, 255) }
end

Regards,

Mike

–

Mike S. [email protected]
http://www.stok.ca/~mike/

The “`Stok’ disclaimers” apply.

4

On Sat, Sep 7, 2013 at 12:50 AM, Hal F. [email protected]
wrote:

/^(25[0-5]|2[0-4]\d|([01])?(\d){1,2}).(25[0-5]|2[0-4]\d|([01])?(\d){1,2}).(25[0-5]|2[0-4]\d|([01])?(\d){1,2}).(25[0-5]|2[0-4]\d|([01])?(\d){1,2})$/

Ruby regular expression; there are a few other features and functions,
EOS
else
puts “Invalid”
end

Reminds me a bit of something I did almost exactly six years and one
month ago:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/263785

:wink:

Cheers

robert

5

On Sep 7, 2013, at 11:02 , Mike S. [email protected] wrote:

I would usually decompose the text using a regular expression and then do the
validation using code, for example something like:

def ipv4_address?(string)
md = /\A (\d{1,3}) . (\d{1,3}) . (\d{1,3}) . (\d{1,3}) \z/x.match string
md && md.captures.all? { |num| num.to_i.between?(0, 255) }
end

You know what’s even better? Not writing anything:

require ‘ipaddr’
=> true
i = IPAddr.new(“192.168.2.100”)
=> #<IPAddr: IPv4:192.168.2.100/255.255.255.255>
i = IPAddr.new(“192.168.2.257”)
IPAddr::InvalidAddressError: invalid address

6

Suit yourself. I put off working on that until September, i.e.,
I started three days ago.

But as you are “out,” I suppose you will never see this anyway.

Hal

7

In this case, very true. I have only touched the ipaddr lib
once, but I see it to be very useful.

Hal

8

I will look at this when I have time.

It would not be the first time you were six years ahead of me. :slight_smile:

Hal

9

Mike,

You’re correct, of course. Multiline regular expressions are
much more readable in general.

Many would argue that the entire project is not worthwhile at all.

My personal opinion is that there is a threshold (which is itself a
matter
of opinion) where regexes become needlessly difficult to read.

Hal

10

On Mon, Sep 9, 2013 at 5:06 PM, Hal F. [email protected] wrote:

I will look at this when I have time.

It would not be the first time you were six years ahead of me. :slight_smile:

Hm, maybe then I should ask you whether you take over maintenance of
my grave - then I’m sure it looks nice for at least six years. :wink:

Cheers

robert

11

I had seen Verbal Expressions before I started my own project, but
never saw hexpress until a couple of weeks ago.

I think they’re both worthy projects, as the concept itself is a worthy
one (in my opinion).

All three projects are similar in spirit and intent, but in
implementation
they are different. Obviously I like my own better. Arguably it is “more
different” from these other two than they are from each other.

Hal

On Thu, Sep 26, 2013 at 6:24 PM, Eric C. <

12

+1 for the choosen name Regexador!

Abinoam Jr.
(From Brazil :wink: )

13

The newest Ruby Weekly pointed out two other more-friendly ways of doing
regexes:

http://krainboltgreene.github.io/hexpress/?utm_source=rubyweekly&utm_medium=email

On Mon, Sep 9, 2013 at 11:53 AM, Robert K.