This contains my current working progress of reading through SICP 2nd edition. The series of video lectures given by Harold Abelson and Gerald Sussman provided great help in understanding the material.
mit-scheme was used to evaluate the solutions in this repository.
In order to get an inexact decimal representation of a rational number, use the procedure exact->inexact e.g. (exact->inexact (/ 1 2)).
- To study computer science is to learn how to formalise intuitions about process
- Declarative knowledge - what is true
- Imperative knowledge - how to
- What is a process?
- Directed by patterns of rules called procedures
- This course (and moreover the field of computer science) essentially deals with techniques for controlling complexity
- In regular engineering the limits of complexity are constrained by the physical world
- The constraints in building large software systems are the limitations of our own mind
- Computer science is an abstract form of engineering, ignoring the constraints imposed by reality
A recursive definition of approximating √x using Heron's method:
(define (sqrt x)
(define (average x y)
(/ (+ x y) 2))
(define (improve guess)
(average guess (/ x guess)))
(define (good-enough? guess)
(< (abs (- (square guess) x))
0.001))
(define (try guess)
(if (good-enough? guess)
guess
(try (improve guess))))
(try 1))Lecture summary:
- In creating programs, we are expressing imperative knowledge
- Lisp combines the following as a means to construct programs
- Primitive elements
- Means of combination
- Means of abstraction
-
In order for a programmer to construct programs in an effective manner, he must understand the relationship between the things he writes and the behaviour of the process that he is attempting to control
- This lecture will establish this connection in a clear a way as possible
-
We will understand how particlar patterns of procedures and expressions, cause particular patterns of execution and behaviour from the processes
-
If we are to understand processes and how to control them, then we have to have a mapping from the mechanisms of our procedure into the way the processes behave
- We will use a formal mechanical model to understand how a machine could execute procedures (whether the machine actually does this is irrelevant)
-
Substitution model is the simplest way for understanding how procedures yield processes
- Evaluate the operator to get procedures
- Evaluate the operands to get arguments
- Apply the procedure to the arguments
- Copy the body of the procedure, substituting the arguments supplied for the formal parameters of the procedure.
- Evaluate the resulting new body
-
The key to understanding complicated things is to know what not to look at (ignore the details)
Kinds of expressions
- Numbers
- Symbols
- Lambda expressions
- Definitions
- Conditionals
- Combinations