The final form of loop to consider is known as a recursive function. This is a function that calls itself until a condition is met. In pseudocode, the function looks like this:

float my_function(i32:a: i32) 
{ 
    // do something with a 
    if (a != 32) 
    { 
        my_function(a); 
    } 
    else 
    { 
        return a; 
    } 
} 
 

An actual implementation of a recursive function would look like this:

// 04/recurse-1/src/main.rs
fn recurse(n: i32)  
{ 
     let v = match n % 2  
     { 
         0 => n / 2, 
         _ => 3 * n + 1 
     }; 
     println!("{}", v); 
   
     if v != 1  
     {  
         recurse(v)  
     } 
} 
 
fn main()  
{  
     recurse(25)  
} 
 

The idea of a recursive function is very simple, but we need to consider two parts of this code. The first is the let line in the recurse function and what it means:

let v = match n % 2  
     { 
         0 => n / 2, 
         _ => 3 * n + 1 
     }; 

Another way of writing this is as follows:

let mut v = 0i32; 
if n % 2 == 0 
{ 
     v = n / 2; 
} 
else 
{ 
     v = 3 * n + 1; 
} 

The second part is that the semicolon is not being used everywhere. Consider the following example:

fn main()  
{  
     recurse(25)  
}