From: Geoff Stanley <geoffstanley@...>
Date: 2006-05-24T02:22:09+09:00
Subject: Re: IRB'ing within a program

Logan Capaldo wrote:
> Here's a "solution" involving IO.popen:
> 
> % cat irb_remote.rb
> puts "Welcome to my pseudo irb frontend. Good luck with this."
> 
> IO.popen('irb', 'r+') do |irb|
>    while line = gets
>      irb.puts line
>      puts irb.gets
>    end
> end

Hal Fulton wrote:
> Well, how about starting irb in another process and talking to it
> via pipes?

Logan and Hal, this sounds like a good idea. However, as Logan's code 
illustrated, pipes are difficult to get working right. I was just 
playing around with them myself; I've discovered a few problems that 
might not be overcome.

First, the code that I was using:
    irb = IO.popen('irb', 'r+')
    loop do
        print ">> "
        irb.puts gets
        irb.gets        # Gets the line that we just put.
        puts "=> #{irb.gets.chomp.inspect}"
    end

Now, the problems:
1) Everything we get back is a string. 1+2 should return the Fixnum 3, 
but we read that Fixnum 3 through the pipe as a string. To overcome 
this, we'd have to know what type of value we should get in return. 
That's basically redoing a good portion of irb.

2) This code doesn't get lines in the right proportion. It works for 
basic things like '1+2' and 'foo = 42', but for a multiline piece of 
code, such as a method definition, it breaks down:
    >> def foo
       puts "bar"
    end
    foo
    ....... hello?
As you can see, I got no output back.

Any way popen could be used more effectively? I don't want to have to 
reimplement irb -- that would be a lot of work, I imagine.

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