origin link sicp 1
Black box(module)
(* x (+ a b)) First scene: Every parentheses is a container called black box, we can take a and b as to varible, like number, electric signal, whatever, we add them, then mul or expand them x times.
tips
primitive elements + : operator 17.4 : number means of combination (+ 3 17.4 5) means of abstration It’s a tree, but we write it as a plain text formation.
define
varible:
(define a (* 5 5))
// the above a will be like 5 * 5(expression could be varible)function:
(define (square x) (* x x))
(square (square (square 5)))sweet:
(define square
(lambda (x) (* x x))
)this seems like every define is a process.
condition:
(if (< x 100) (display "lower than 100"))Recursive defination (Heron square root)
Hreon : get the square root of x
make a guess
improve guess by get the average of guess and x/guess
good-enough? done : improve guess
tips: good-enough? how close between x/guess (< abs (- (square guess) x) .001)
Analyze as a tree: (root 2) (try 1 2) (try (improve 1 2) 2) (try 1.5 2)
Important note:
(define a (* 5 5))
(define (d) (* 5 5))output:
a -> 25
d -> d procedure
(d) -> 25
(a) -> error