Loops

Ferret provides several loop constructs for iteration.

For Loops

Range-based For Loops

Ferret provides two range operators for loops:

• .. - Exclusive end: loops from start to end-1
• ..= - Inclusive end: loops from start to end

// Exclusive: iterates 0 to 9 (10 iterations)
for i in 0..10 {
    io::Println(i);  // Prints: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
}

// Inclusive: iterates 0 to 10 (11 iterations)
for i in 0..=10 {
    io::Println(i);  // Prints: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
}

Loop variables are always declared and scoped to the loop body.

The range operators generate arrays, so this is equivalent to:

let numbers := 0..10;   // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
let numbers_inc := 0..=10;  // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

for i in numbers {
    io::Println(i);
}

You can specify the step/increment with both operators:

// Exclusive with step
for i in 0..10:2 {
    io::Println(i);  // Prints: 0, 2, 4, 6, 8
}

// Inclusive with step
for i in 0..=10:2 {
    io::Println(i);  // Prints: 0, 2, 4, 6, 8, 10
}

Index and Value Pairs

let arr := [10, 20, 30];
for i, val in arr {
    io::Println(i, val);  // Prints: 0 10, 1 20, 2 30
}

Note: The index variable (first in a for i, val in ... loop) is read-only. Loop variables are always mutable otherwise, and you cannot use const for loop iterators.

While Loops

let x := 0;
while x < 5 {
    io::Println(x);
    x = x + 1;
}

This loop continues as long as the condition x < 5 is true.

There is no do-while loop in Ferret; use a while loop with an initial condition instead.