1. Programming Language 就是 Syntax 和 Semantic的集合
2. 两种重要的Semantic: Denotational Semantic : 把一段语言用另外一种语言来表达它的semantic;一般“另一种语言”就是Mathematic。Operational Semantic:把语言看成是状态的转换，(state*var*value)->state
3.lambda calculus:(lambda x (f x)) 就是 f(x), x是它的parameter.
free variable 和 bind variable (lambda x (f x y))
a-equivalent. (lambda x x) = (lambda y y)
b-equivalent. (lambda x M)N = [N/x]M, 用N 把M里面的所有free的x 都进行替换。
4. Side Effect: 如果f(x,y) 函数体内不会改变x, y的值，那么就称之为没有side effect.
5. Types:
compile time checking:
run time checking:
type checking: 显式的定义type
type inference：在runtime根据参数类型，函数类型决定type
Polymorphism
Overloading
type safe: 如果一个语言允许显式的deallocation内存，那么它必然不是完全的type safe的。
6. Control:
Dynamic Scope: for exception handler, follow control link
Static Scope: for variable declarations, follow access link
7.Parameter Pass:
pass by name:
pass by value:
pass by reference
8. Tail Recursive: 对于递归函数来说，它的结果是可以直接从递归部分得到或者是不需要递归。类似于iteration的感觉。其好处在于，每次进行递归的时候，可以不需要保 存当前的环境 f(x) -> f(x,P) P 是continuation of the current state x.
9. Continuation: 我理解为一个函数，represent the remain computation of a current state of a program.所以每当一个程序的状态发生改变（variable value change, declaration...)都会有一个新的state.
callcc 函数
10.Scope:
Control Link: dynamic form
Access Link: static form
11. Total Function & Partial Function
12. L-values :Memory location; R-values :contents
13. Anonymous Function: use function as parameters
14.Object Orientation
dynamic lookup -> code depend on object and message
different from overloading:
overloading: compile time
dynamic lookup: runtime
encapsulation -> you only need to know the interface
inheritance -> relationship between implement
subtyping -> relationship between interface
15. Languages:
OO: Small talk, simula, Self, C++, Java
Functional: ML, Lisp, Haskell
Others: JavaScript, PHP, Python......
