SICP shows a real world code base. It's real world programs that builds up to implementing real world programming languages. Why would you validate if you can

SICP shows a real world code base. It's real world programs that builds up to implementing real world programming languages. Why would you validate if you can parse? If you have a decent chunk of experience in implementing business logic then you know that your quality of life will be destroyed by switches and other inscrutable wormhole techniques up until the point where you learn to use and build around rule engines. SICP shows you how you can tailor your own rule engine, so you won't have to get the gorilla and the jungle when you reach for one in an enterprisey library.