Normally I hate to debug apps — we are big fans of test first, but oh well, sometimes it can be very helpful. The danger starts when one wastes too much time debugging.

Even when using a IDE it can be very handy to get into a irb session at any moment.

You need to install ruby-breakpoints

 require 'breakpoint'
 ..
 if m==0
    puts "m is 0"
    pp xs
    puts ys.to_yaml
    breakpoint
 end
 ..

Useful:

• use CTRL-D (Unix) or CTRL-Z (Windows) or exit to leave the breakpoint and continue running the program
• use exit! to terminate the program from within a breakpoint
• other interesting things to check out include: local_variables, instance_variables, caller, methods
• just type the name of your variable to check its value
• Note that you can enter any type of regular Ruby code into a breakpoint IRB shell. You can even hot patch your deployed code to fix a problem at run-time!

If you are developing a rails app, check out the wiki entry.

I take my break now. Off for yammie food.