what is var in Clojure
var is a special construct used to refer to a named value or function in the current namespace. It is used to hold the reference to a symbol, which can be thought of as a name in the code. The
var construct is used to access and manipulate the value or behavior associated with that name.
In Clojure, variables are immutable by default, meaning their value cannot be changed once assigned. However, the
var construct provides a way to associate a new value with a symbol, effectively redefining the variable. This is done using the
def special form, which creates a new var or updates an existing one.
var construct is commonly used to define and refer to functions and global values in Clojure. It allows you to access and manipulate these values dynamically, providing a flexible way to work with code and data.
Here's an example:
(def x 10) ; define a variable x with the value 10
(println x) ; prints the value of x
(defn add [a b] (+ a b)) ; define a function add
(println (var add)) ; prints the var associated with the add function
(def add (var add)) ; redefine the add var with a new value
(println (var add)) ; prints the updated var associated with the add function
In the example above, the
def form is used to define a variable
x with the value 10. The
println function is then used to print the value of
x. Similarly, the
defn form is used to define a function
add, and the
var construct is used to access and manipulate the var associated with the
By using the
var construct, you can dynamically redefine and access functions and values in Clojure, providing a powerful mechanism for code manipulation and flexibility.