本章首先对语言做简要介绍。目的是通过实际的程序向读者介绍语言的本质要素，而不是一下子就陷入到具体细节、规则及例外情况中去。-The first chapter of language are introduced briefly. Purpose is through the practical program readers are introduced to the essence of language elements, and not suddenly into specific details, rules and exceptions.