Defining variables and scopes learning emacs lisp 4

diving deep into variables and scopes in emacs lisp

this tutorial will guide you through the intricate world of variables and scopes in emacs lisp. understanding these concepts is crucial for writing well-structured, maintainable, and predictable code. we'll cover the different types of variables, their associated scopes, and how to effectively manage them in your emacs lisp programs. we'll also touch upon best practices and potential pitfalls to avoid.

**1. what is a variable?**

at its core, a variable is a symbolic name that holds a value. think of it as a container that can store information. this information can be anything from numbers and strings to lists and even functions. variables allow you to give names to pieces of data, making your code more readable and easier to work with.

**2. variable types in emacs lisp**

emacs lisp distinguishes primarily between two kinds of variables based on their intended usage and scope:

* **global variables (dynamically scoped):** these variables are defined at the top level and are accessible from anywhere in the current emacs session. their values are determined by the *dynamic* calling context. this means that when a function accesses a global variable, it uses the *most recently bound* value of that variable, considering the current execution stack.

* **lexically bound variables (lexically scoped):** these variables are declared within a specific block of code (like a `let` form or a function definition) and are accessible only within that block and its nested blocks. their values are determined by the *static* lexical structure of the code. this means that the value of a lexically bound variable is determined by where it is *defined* in the source code, not necessarily where it is *called*.

let's explore each in detail.

**3. global variables: dynamic scope**

* **defining global variables:** you define a global variable using `defvar` or `defcustom`.

* `defvar`: this is used to define a va ...

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