class Sass::Stack

def deep_copy
  stack = Stack.new
  stack.frames.replace frames
  stack
end

def initialize
  @frames = []
end

def to_s
  Sass::Util.enum_with_index(Sass::Util.enum_cons(frames.reverse + [nil], 2)).
      map do |(frame, caller), i|
    "#{i == 0 ? "on" : "from"} line #{frame.line}" +
      " of #{frame.filename || "an unknown file"}" +
      (caller && caller.name ? ", in `#{caller.name}'" : "")
  end.join("\n")
end

def with_base(filename, line)
  with_frame(filename, line, :base) {yield}
end

def with_frame(filename, line, type, name = nil)
  @frames.pop if @frames.last && @frames.last.type == :base
  @frames.push(Frame.new(filename, line, type, name))
  yield
ensure
  @frames.pop unless type == :base && @frames.last && @frames.last.type != :base
end

def with_import(filename, line)
  with_frame(filename, line, :import) {yield}
end

def with_mixin(filename, line, name)
  with_frame(filename, line, :mixin, name) {yield}
end