Second is the use of general concepts, models, and terminology from my Programming Language Principles course. Readers should have no trouble adapting the concepts introduced in this text to other programming languages. Third is the notion of meta programming. In this context the language being described or analyzed is referred to as the object language . For example, the meta language used in this book is English, while the object language is Scheme.
Most programming languages make a sharp distinction between programs and data.
Scheme doesn't have such prejudices, and this makes Scheme an excellent meta language.