# IRB module with non-blocking asynchronous gets **URL:** \ **Category:** ruby-talk\ **Created:** [25 August 2007 08:09 UTC](https://rubytalk.org/t/irb-module-with-non-blocking-asynchronous-gets/40180 "2007-08-25T08:09:17Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Shane\_Liesegang](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@Shane\_Liesegang](https://rubytalk.org/u/Shane_Liesegang)\ **Post date:** [25 August 2007 08:09 UTC](https://rubytalk.org/t/irb-module-with-non-blocking-asynchronous-gets/40180/1 "2007-08-25T08:09:17Z")
Is there a way to use the IRB module so that it evaluates code on-demand only instead of running in a constant loop? I don't need to use readline and have IRB wait for input -- I can trigger its need to evaluate from elsewhere in the program. I was hoping, though, that I could have the gets function from my IRB::StdioInputMethod subclass return a properly formatted string, let IRB do its thing, and then give me back control until it was needed again. It seems, though, that the eval\_input function just keeps executing gets and never returns control. I understand that's the intended behavior of eval\_input, but I'm a little surprised there's not a more asynchronous way of requesting evaluation. Am I just approaching the problem from the wrong angle? I keep feeling like Ruby has to provide a way to do what I'm after, but I haven't been able to track it down thus far. Any help would be appreciated. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![James\_Edward\_Gray\_II](https://avatars.discourse-cdn.com/v4/letter/j/ea5d25/32.png) [@James\_Edward\_Gray\_II](https://rubytalk.org/u/James_Edward_Gray_II)\ **Post date:** [26 August 2007 03:17 UTC](https://rubytalk.org/t/irb-module-with-non-blocking-asynchronous-gets/40180/2 "2007-08-26T03:17:36Z")
I'm working on my glue code speech for Lone Star Rubyconf today so my first thought was: #!/usr/bin/env ruby -wKU class IRbOnDemand    def initialize      @irb = IO.popen("irb -f --simple-prompt --noreadline", "r+")    end    def run(ruby)      @irb.puts ruby      @irb.flush      @irb.each do |line|        return eval($1) if line =~ /\A=\>\s\*(.+)/      end    end end irb = IRbOnDemand.new result = irb.run %Q{a = %w[words] \* 3} puts "Result: #{result.inspect}" puts "Doing other things..." sleep 3 result = irb.run %Q{a} puts "Result: #{result.inspect}" \_\_END\_\_ Is that what you are after? If it is, do we really need IRb at all? How's this: #!/usr/bin/env ruby -wKU class IRbOnDemand    def initialize      @binding = binding    end    def run(ruby)      eval ruby, @binding    end end irb = IRbOnDemand.new result = irb.run %Q{a = %w[words] \* 3} puts "Result: #{result.inspect}" puts "Doing other things..." sleep 3 result = irb.run %Q{a} puts "Result: #{result.inspect}" \_\_END\_\_ James Edward Gray II > **···** > > On Aug 25, 2007, at 3:09 AM, Shane Liesegang wrote: > > > Is there a way to use the IRB module so that it evaluates code on-demand > > only instead of running in a constant loop? ---
**Author:** ![Shane\_Liesegang](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@Shane\_Liesegang](https://rubytalk.org/u/Shane_Liesegang)\ **Post date:** [27 August 2007 14:46 UTC](https://rubytalk.org/t/irb-module-with-non-blocking-asynchronous-gets/40180/3 "2007-08-27T14:46:05Z")
Hi James. Thanks for the recommendations. James Gray wrote: > Is that what you are after? If it is, do we really need IRb at all? > How's this: I could just use eval to run the strings; that's true. I was hoping to leverage IRB's prompt mechanism and the ability to define functions on the fly. As below: > **···** > > ----- > irb(main):001:0\> def test > irb(main):002:1\> puts "testing..." > irb(main):003:1\> end > =\> nil > irb(main):004:0\> test > testing... > =\> nil > irb(main):005:0\> > ----- > > I'm finding that it's pretty tricky, though. I managed to make it > non-blocking for a single line by overriding eval\_input and having it > break after evaluating a line instead of waiting for input. That seems > to work fine, but when doing any kind of multi-line input, it still goes > into a loop that it doesn't want to return from. > > It seems like IRB, to its core, is based on constantly waiting for > input, and trying to make it work in an on-demand fashion is like > running uphill. I'm still rooting through its source, trying to find the > spots where I can poke at it to make it work that way, but it's slow > going with a large mass of interrelated code that's not terribly easy > for humans to parse. 🙂 > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Shane\_Liesegang](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@Shane\_Liesegang](https://rubytalk.org/u/Shane_Liesegang)\ **Post date:** [29 August 2007 18:08 UTC](https://rubytalk.org/t/irb-module-with-non-blocking-asynchronous-gets/40180/4 "2007-08-29T18:08:45Z")
For anyone still reading this thread (or who stumbles across it in the future), I have been able to solve the string continuation problem -- it may be a bit inefficient, but I run my own processing on the line before trying to pass it to the lexer. If I determine that it's the start of a string continuation, I set the flags appropriately. No code in pastie this time, but the algorithm for finding unfinished strings is pretty straightforward, provided you cover all the cases provided in Ruby (single quotes, double quotes, %q, %w, %x, %Q, %W, %X, and heredocs). I leave it as an exercise to the reader. 🙂 > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).