Proc vs lambda: when a return is used inside a proc, it does something called a non-local return — that is, instead of returning from the code executing inside the proc, it returns from its calling context.

lambda_vs_proc_return.rb

def return_proc
  p = Proc.new { return "Now you see me" }
  p.call
  return "Now you don't!"
end

return_proc
# => "Now you see me"

def return_lambda
  l = lambda { return "Now you see me" }
  l.call
  return "Now you don't!"
end

return_lambda
# => "Now you don't!"

via: http://www.dev.gd/20130107-know-your-closures-blocks-procs-and-lambdas.html