Write chapter 1 summary
This commit is contained in:
57
README.md
57
README.md
@@ -12,3 +12,60 @@ execute `pacman -S mit-scheme` to install it. Then run the scripts via
|
|||||||
|
|
||||||
**This is currently (2020/12/16) work in progress.**
|
**This is currently (2020/12/16) work in progress.**
|
||||||
|
|
||||||
|
|
||||||
|
# Chapter 1
|
||||||
|
|
||||||
|
The first chapter of SICP starts by explaining the Scheme syntax. The first
|
||||||
|
couple of exercises are simple enough. However, already at 1.5, the book
|
||||||
|
foreshadows some of the difficulty that is about to come.
|
||||||
|
|
||||||
|
```scheme
|
||||||
|
(define (p) (p))
|
||||||
|
(define (test x y)
|
||||||
|
(if (= x 0) 0 y))
|
||||||
|
```
|
||||||
|
|
||||||
|
The goal is to decide whether Scheme uses applicative-order-evaluation or
|
||||||
|
normal-order-evaluation based on the above code. I have initially found the
|
||||||
|
exercise confusing, but the code triggering an infinite loop is a clear
|
||||||
|
indication of Scheme (or at least my version of Scheme, MIT Scheme) using
|
||||||
|
applicative-order-evaluation.
|
||||||
|
|
||||||
|
After this exercise, things get more comfortable again. The book proceeds to
|
||||||
|
introduce if-else clauses, conditionals, as well as recursion. The book uses
|
||||||
|
these primitives to compare iterative and recursive procedures based on a couple
|
||||||
|
of typical CS example functions such as computing Fibonacci numbers, greatest
|
||||||
|
common divisor, and fast exponentiation.
|
||||||
|
|
||||||
|
Two new insights I had how using modulo instead of subtracting the divisor
|
||||||
|
speeds up the GCD algorithm I learned in middle school and how exponentiation
|
||||||
|
can run in O(log n) by halving even exponents.
|
||||||
|
|
||||||
|
I wasn't able to prove the Golden Ration exercise at the time of working through
|
||||||
|
this chapter. My knowledge of induction and proofs was too limited. I found that
|
||||||
|
depressing at the time, and I wish they hadn't included that exercise.
|
||||||
|
|
||||||
|
Nevertheless, the book moves on to further essential CS concepts such as Prime
|
||||||
|
numbers and the Fermat primality test. Funnily enough, I used that probabilistic
|
||||||
|
Prime test for a Project Euler exercise, wondering why I wasn't able to get the
|
||||||
|
correct results. It turns out that this test detects probable primes (the book
|
||||||
|
mentions that a little later and introduces the Miller-Rabin test that
|
||||||
|
pseudoprimes cannot fool). On the one hand, it was cool to use an algorithm from
|
||||||
|
a book directly. On the other hand, I was undoubtedly a bit annoyed by that
|
||||||
|
story.
|
||||||
|
|
||||||
|
The book moves on to discuss the runtime of some of the algorithms discussed to
|
||||||
|
this point. It introduces some other mathematical concepts, such as calculating
|
||||||
|
roots via the fixed-point method, Euler expansions, and the Newton method for
|
||||||
|
finding minima/maxima. It was cool to see how the fixed-point method can be used
|
||||||
|
to implement the Newton method if you plug the derivate of a function into it. I
|
||||||
|
did my project presentation for math in high school about the Newton method. So
|
||||||
|
this brought up cool memories. I wish I still had that presentation.
|
||||||
|
|
||||||
|
Finally, SICP introduces the evaluation model for stateless functions and
|
||||||
|
concludes with some exercises that require second-order procedures: procedures
|
||||||
|
that take other procedures as arguments.
|
||||||
|
|
||||||
|
# Chapter 2
|
||||||
|
|
||||||
|
|
||||||
|
|||||||
Reference in New Issue
Block a user