class Sass::Script::Parser

def expr
  interp = try_ops_after_interp([:comma], :expr) and return interp
  line = @lexer.line
  return unless e = interpolation
  arr = [e]
  while tok = try_tok(:comma)
    if interp = try_op_before_interp(tok, e)
      return interp unless other_interp = try_ops_after_interp([:comma], :expr, interp)
      return other_interp
    end
    arr << assert_expr(:interpolation)
  end
  arr.size == 1 ? arr.first : node(List.new(arr, :comma), line)
end