This is the summary of SICP
- Computational process
- abstract beings that inhabit computers
- data
- other abstract beings upon which processes manipulate
- program
- pattern of rules for evolution of the process
- programming language
- contains symbolic expressions that prescribe the tasks that processes perform
Every programming language serve as a framework within which one forms complex ideas about processes from simple ideas. There are 3 mechanisms to accomplish that:
- primitive expressions
- simplest entities
- means of combination
- by which compound elements are built from simpler ones
- means of abstraction
- by which compound elements are named and manipulated as units
In programming we deal with 2 kinds of elements: data and procedures.
- data
- values which we manipulate
- procedure
- descriptions of rules for manipulating the data
Data and procedures actually are not so distinct.
- combination
- expression formed by list of expressions in parentheses for denoting procedure application
- operator
- left-most element in the list
- operands
- remaining elements in the list
- procedure
- the value of operator
- arguments
- values of operands
Value of combination is got by applying the procedure specified by the operator over the arguments.
- Prefix notation
- convention of placing operator before operands
- nestedness
- ability of a combination having elements that are themselves combinations
- variable
- identified by name
- value
- the computational object behind the variable
Example of variable definition
(define size 2)From now on we can refer to the value 2 by the name size.
- environment
- memory that keeps track of the name-object pairs
General evaluation rule:
- Evaluate the sub-expressions of the combination
- Apply the procedure to the arguments
This evaluation rule is recursive.
- recursive process
- the process that includes the need to invoke itself as one of its steps
- tree accumulation
- recursive process of evaluating evaluating expressions downward and then accumulating values upward
- special forms
- expressions that are not executed according to this evaluation rule, like
define
Some elements of Lisp adhere to the requirements of a programming language
- primitive expressions : numbers and arithmetic operations
- means of combination : nesting of combinations
- means of abstraction : definitions
- procedure definition
- method, by which a compound operation can be named and referred to as a unit
Example of procedure definition
(define (square x) (* x x))General form of a procedure definition is
(define (<name> <formal parameters>) <body>)
Defined procedures can be combined too:
(define (sum-of-squares x y)
(+ (square x) (square y)))