SICP(Structure and Interpretation of Computer Programs)

1.If the meta-circular is a machine , what is the core of it, or what is the engine part of it?

The answer is two basic procedures  : Eval and Apply.

The evaluation process can be described as the interplay between two procedures: eval and apply.

2.Eval refers Apply, and Apply also refers Eval. It's like hand A drawing hand B, hand B drawing hand A . it shows up a cycle.(see figure below)

Drawing hands

3.Eval  is reducing.   Apply is connecting.

4.Lambda-Calculus can help us to understand it easily.

Apply is like Application : (M N) , M connect N, Apply is like a position-man

Eval is like β-reduction : ((λx.M) E) → (M[x:= E]) , Eval is like a performer.

5.It is like a strange Loop, just like consciousness being in human's brain.

"I" can feel "I" self, so , there must be two basic items , like Eval and Apply.

This idea comes from the book : "I AM A STRANGE LOOP" - Douglas Hofstadter.

6.All of this chapter is in the high-level perspective, in this layer, we can not see clear why eval and apply be build . It is like we in the picture drawing hands , we can not know who build hands itself. We must jump out of that picture, we can understand the picture be created by paper and pen.

Chapter 5 will talk about the deep-level ,  see what is the paper and pen create the eval and apply.

It is the Register Machines. It will shows the physic level of calculate.