a_caller.rb

require 'binding_of_caller'

BacktraceEntry = Struct.new(:file, :line, :method_name) do
  def to_s
    "#{file}:#{line}: " + (method_name ? "in #{method_name}" : "at toplevel")
  end
end

def bindings_before(b)
  ary = []

  (0..Float::INFINITY).each do |n|
    ary << b.of_caller(n)
  end
rescue # raises a plain RuntimeError when it fails
  ary
end

def caller
  bindings_before(binding.of_caller(0)).map do |b|
    BacktraceEntry.new(b.eval("__FILE__"),
                       b.eval("__LINE__"),
                       b.eval("__method__")) # hope the method hasn't changed
  end
end

def foo
  loop do
    puts caller
    break
  end
end

foo