Scheme is an easy language to learn once you get over your fear of parentheses.
This section shouldn't be strenuous reading for the members of this book club, but don't think you should skip it!
On display are two pedagogical techniques A&S use that I admire. First, they lay out in clear terms how to conceive of evaluation ("the substitution model") and then stress that it's merely a model, that we'll examine more accurate models later. Second, they explain aspects of Scheme not as divine truths from on high but as design decisions. They show how normal-order evaluation could also be used for a certain class of problems and explain why applicative-order was chosen instead.
I also appreciate definitions of concepts like block structure and lexical scoping. I understood them intuitively but couldn't put a name to them until now.
My code and short answers for this section are here.
The early exercises feel like the start of a Metroid game. You know you're going to get more powerful tools soon, but right now you just have a skimpy little gun. The constraints can force you to be creative, but it can also be annoying.
Take for example Exercise 1.5:
Define a procedure that takes three numbers as arguments and returns the sum of the squares of the two larger numbers.
I wanted to find the two smallest arguments and then just do computation on those. However, I haven't "unlocked" simple data structures like lists or tuples yet, so I had no way to do that. Here's what I did instead. It feels dirty.
; Is candidate no greater than x and y? (define (smallest? candidate x y) (and (<= candidate x) (<= candidate y))) (define (sum-of-squares x y) (+ (square x) (square y))) (define (sum-of-squares-of-two-largest x y z) (cond ((smallest? x y z) (sum-of-squares y z)) ((smallest? y x z) (sum-of-squares x z)) ((smallest? z x y) (sum-of-squares x y))))
Next time on SICP
Recursion and big O notation with a side of number theory.
As always, I'd love to know what you thought of this section, dear reader. Let me know in the comments!