module Sass::Value

def [](index)
  at(index)
end

def assert_boolean(name = nil)
  raise error("#{self} is not a boolean", name)
end

def assert_calculation(name = nil)
  raise error("#{self} is not a calculation", name)
end

def assert_color(name = nil)
  raise error("#{self} is not a color", name)
end

def assert_function(name = nil)
  raise error("#{self} is not a function", name)
end

def assert_map(name = nil)
  raise error("#{self} is not a map", name)
end

def assert_number(name = nil)
  raise error("#{self} is not a number", name)
end

def assert_string(name = nil)
  raise error("#{self} is not a string", name)
end

def at(index)
  index < 1 && index >= -1 ? self : nil
end

def bracketed?
  false
end

def eql?(other)
  self == other
end

def error(message, name = nil)
  Sass::ScriptError.new name.nil? ? message : "$#{name}: #{message}"
end

def sass_index_to_array_index(sass_index, name = nil)
  index = sass_index.assert_number(name).assert_integer(name)
  raise error('List index may not be 0', name) if index.zero?
  if index.abs > to_a_length
    raise error("Invalid index #{sass_index} for a list with #{to_a_length} elements", name)
  end
  index.negative? ? to_a_length + index : index - 1
end

def separator
  nil
end

def to_a
  [self]
end

def to_a_length
  1
end

def to_bool
  true
end

def to_map
  nil
end

def to_nil
  self
end