Lecture notes

Unit 5

Create Linked Environments

When we call a function :

1. Create a new environment. Its parent pointer points to the current environment.
2. In the new environment, we create storage places for each formal parameter.
3. Fill in these places with the values of the actual arguments.
4. Evaluate the function body in the new environment.

Note! 在UW programming languages课程中，hw5实现了一个scheme-like的 tiny-language，在其中用到了function closure，和这里介绍的方法略有不同。

environments needs to

1. map variables to values
2. point to the parent environment

We’ll use Exceptions to simulate the return statements in our js interpreter

Phrasing “return” as an exception allows us to break out of any nested statement evaluation and return to the caller immediately.

provided code中的global_env_update是否不合理

提供的jsinterp.py程序中，有一个global_env_update函数，其类似于env_lookup函数，如果 在当前env中找不到vname，则在其parent env中继续找，且若在global_env中还找不到，就会在 global_env中新建variable，这是否不合理