One small note, as pointed out in http://innig.net/software/ruby/closures-in-ruby.rb http://innig.net/software/ruby/closures-in-ruby.rb posted by arohner above:

One small note, as pointed out in http://innig.net/software/ruby/closures-in-ruby.rb http://innig.net/software/ruby/closures-in-ruby.rb posted by arohner above: although in 1.8 proc is an alias for lambda, in 1.9 it's now an alias for Proc.new.