class Sass::Script::Parser

def string
  return number unless first = try_tok(:string)
  return first.value unless try_tok(:begin_interpolation)
  line = @lexer.line
  mid = parse_interpolated
  last = assert_expr(:string)
  interp = StringInterpolation.new(first.value, mid, last)
  interp.line = line
  interp
end