Re: negative grep

On Sat, Jan 14, 2012 at 2:24 PM, Robert Klemme
<[e-mail]>wrote:

> On Sat, Jan 14, 2012 at 1:51 PM, Josh Cheek <[e-mail]> wrote:
> > On Sat, Jan 14, 2012 at 6:06 AM, Robert Klemme
> > <[e-mail]>wrote:
> >
> >>
> >> It's impossible because
> >>
> >>  - you cannot change behavior of !
> >>
> >
> > You can do this (I'm not advocating it), but IDK how you would actually
> > negate it.
> >
> > class Regexp
> >  def !@
> >    /some sort of negation of #{source}/
> >  end
> > end
> >
> > abc = /abc/
> > !abc # => /some sort of negation of abc/
>
> Oh, I wasn't aware of this.  Thank you for the education!
>
> The way to use it would probably be to create a wrapper instance which
> reverses semantics of the original's Regexp instance and sets global
> variables accordingly (if this is possible; not sure in the case of
> $1, $2 etc. because of their special nature).
>
> Still the other obstacle would prevent making !enum.grep(/foo/) return
> what is intended.  You could only do enum.grep(!/foo/).  There is a
> potential though to break other code which relies on different boolean
> behavior of Regexp instances so the approach with #grep_v or an
> explicit Regexp#negate would be better.
>

I meant my earlier proposal

> Negation could be an option for the Enumerable grep command

more along these lines:

describe "grep_with_options" do

  it "works as before with 1 arugment" do
    %w{abc def ghi}.grep(/abc/).should == %w{abc}
  end

  it "negates the selection with 'v'" do
    %w{abc def ghi}.grep(/abc/, 'v').should == %w{def ghi}
  end

  it "can be chained" do
    %w{abc adf agh bcd efd}.grep(/^a/).grep(/c/,'v').should == %w{adf agh}
  end

  it "can select lines after with A" do
    pending("TODO")
    %w{abc def ghi}.grep(/abc/, 'A1').should == %w{abc def}
  end

end

# a naive implementation
module Enumerable
  def grep(cond, *select_options)
    negate_matches = select_options.include?('v')
    if negate_matches
      reject {|e| cond === e}
    else
      select {|e| cond === e}
    end
  end
end

Just the 'v' option to grep would already be useful
(and it would match with the request from the OP).

There are other grep options that I use quite often too
and could be implemented (-A -B -C -c ...) similarly.

Peter