The document provides an introduction to formal language, emphasizing grammar's role in language definition and the memory life cycle in programming languages, particularly JavaScript. It highlights JavaScript's lexical scope and contrasts it with dynamic scoping through case studies. The text also addresses variable binding and its implications within different namespaces in JavaScript.

1. Schwannden 2020/8/19
Names, Bindings,
Scopes
A gentle introduction to the formal language

2. Formal Language

3. Formal Language
How to formally define language

4. Formal Language
How to formally define language

5. Formal Language
How to formally define grammar

6. Formal Language
How does grammar generate language

7. • Each language has different grammar that strictly defines its
syntax. This is one of the reason why complicated language can
still be designed with a correct syntax analyses.
• Human language usually can not be defined as the simple kind of
grammar mentioned (CFG), so human bran is actually amazing.
• Different type of grammar have different power to define
language with different capability (will not be discussed).
• Language design usually does not start from grammar design,
grammar design comes after.
• Knowing the grammar, with the concept of expression and value
help us learn and formalize one language really fast (TBD in the
future)
Formal Language
Implication

8. Binding

9. Binding
Definition

10. Binding
Definition

11. Binding
Definition

12. Binding
Type of Variable

13. Binding
Type of Variable

14. Binding
Type of Variable

16. Binding
Type of Variable

17. Binding
Type of Variable

18. Binding
Case Study - Javascript
Regardless of the programming language, the memory life cycle is pretty much always the same:
1. Allocate the memory you need
2. Use the allocated memory (read, write)
3. Release the allocated memory when it is not needed anymore
The second part is explicit in all languages. The first and last parts are explicit in low-level languages but are mostly implicit in high-
level languages

19. Binding
Case Study - Javascript

20. Binding
Case Study - Javascript

21. Binding
Case Study - Javascript GC (Reference Counting)

22. Binding
Case Study - Javascript GC (Reference Counting)

23. Binding
Case Study - Javascript GC (Mark-and-Sweep Algorithm)

24. Scope

25. Scope
Definition

26. Scope
Case Study - Javascript Scope

27. Scope
Case Study - Javascript Scope
To be clear, JavaScript does not, in fact, have dynamic scope. It has
lexical scope. Plain and simple. But the this mechanism is kind of like
dynamic scope.

28. Scope
Case Study - Javascript Scope

29. Scope
Case Study - Javascript Scope

30. Scope
Dynamic Scoping

31. Scope
Static Scoping

32. Scope
Static Scoping

33. Scope
Static Scoping

34. Scope
Static Scoping

35. Scope
Namespaces

36. Scope
Namespaces
Javascript
function f(x) {return x;}
var f = f // legal, because function and var are in different name space.
var g = g // undefined, binding does not happen after assignment
function fac(n) { return n <= 1 ? 1 : n * fac(n-1) } // legal, function name is visible to its body
Scala
def f(n: Int): Int = n
val f = f // illegal, because function and var are in the same name space.
val g = g // illegal, binding does not happen after assignment