class Sass::Script::Parser

def defn_arglist(must_have_default)
  return unless c = try_tok(:const)
  var = Script::Variable.new(c.value)
  if try_tok(:single_eq)
    val = assert_expr(:concat)
  elsif must_have_default
    raise SyntaxError.new("Required argument #{var.inspect} must come before any optional arguments.", @line)
  end
  return [[var, val]] unless try_tok(:comma)
  [[var, val], *defn_arglist(val)]
end