you can call a proc via: f === :arg!

when-proc.rb

# ruby 1.9 supports 4 ways to call a proc! ex:  f =->n {[:hello, n]}; f[:ruby]; f.call(:ruby); f.(:ruby) 
#
# turns out, you can also call a proc via proc === :arg -- which means you can use proc's in when clauses!
# ruby doc: http://ruby-doc.org/ruby-1.9/classes/Proc.html#M001165
#
# ... kudos to @chadfowler for the tip!
#
# (note: works on 1.8.7 as well :-))

def should_i_upgrade?
  awesome = Proc.new do |version|
    case version
      when "1.9.2" then true
      when "1.8.7" then false
    end
  end

  case RUBY_VERSION
    when awesome
      puts "congrats, you're awesome"
    else
      puts "not really, you should: rvm install 1.9.2"
  end
end

should_i_upgrade?