What are the Clojure variables?

Key takeaways:

• Variables in Clojure are immutable, meaning their values cannot be changed after assignment. This adheres to functional programming principles, promoting safer and more predictable code.

• Local variables created using let for lexical scoping or binding for dynamic scoping, Clojure’s local variables cannot be reassigned once bound, reinforcing immutability.

• Global variables defined using def, global variables can be modified and accessed across the entire namespace, but their use should be minimized to preserve functional programming practices.

• Function parameters treated as variables within the function’s scope, parameters enable passing data into functions, promoting a clear, functional programming style without external variable modification.

• Best Practices for using variables in Clojure are:

1. Minimize global variables and avoid frequent modification.

2. Use function parameters for passing data.

3. Embrace immutability by avoiding variable reassignment and creating new variables for updated values.

• Following immutability and functional programming guidelines helps maintain clear, maintainable, and manageable code in Clojure.

Local variables

The most common way to create local variables in Clojure is by using the let and binding forms. The let form is used for lexical scoping while binding is used for dynamic scoping.

In the code above, we define a function local-variables-example. Inside the let block, we create local variables x and y, and y is derived from x. The values of x and y cannot be modified within the block.

When you run the above code, you will get an error message like the following: Cannot assign to non-mutable: x.

Clojure’s let bindings are immutable. Once a value is bound to a name, that value cannot be changed. The set! function only works with mutable constructs like atoms, refs, or Java interop, not with immutable local variables. This immutability is a core part of Clojure’s design, promoting safer and more predictable code.

Global variables

Global variables in Clojure are created using the def form. These variables are available throughout the entire namespace and can be accessed and modified from any function or code block within the namespace.

In the above example, we define a global variable global-var with an initial value of 44. We can access and modify it from different functions within the same namespace. However, it’s important to note that using global variables should be minimized in functional programming to maintain immutability.

Function parameters

Function parameters in Clojure can also be considered as variables. These are bound within the function’s scope and serve as placeholders for the arguments passed when the function is called.

In the sum function, a and b are parameters representing the arguments passed when the function is called. The result of the function is assigned to the result variable.

Best practices for using variables in Clojure

It’s important to follow functional programming guidelines while working with variables in Clojure in order to preserve immutability and produce clear, manageable code. The following are some recommended procedures:

1. Minimize the use of global variables

Global variables should be used sparingly, and their values should not be modified frequently. When necessary, follow a naming convention that distinguishes them from local variables.

2. Use function parameters

Leverage function parameters to pass data to functions, as it promotes a functional programming style. Avoid modifying variables outside the scope of the function.

3. Avoid reassignment

In Clojure, variables are immutable. Instead of modifying variables, create new variables with updated values. This approach helps in debugging and understanding the flow of data.

Conclusion

Variables are essential for storing and modifying data, but in the Clojure what really sets them different from many other programming languages are their immutability and functional programming concepts. To write clean, manageable Clojure code, one must comprehend lexical and dynamic scoping and adhere to recommended practices. The complete power and elegance of Clojure can be fully utilised by developers in their projects by carefully selecting variables and following the guidelines of functional programming.