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Loop

Introduction​

The Wave language provides loops to handle situations where the same code needs to be executed multiple times. Loops are used to continually execute code while a specific condition is met or for a set number of repetitions.

This allows for expressing repetitive tasks with concise and clear code without the need to repeatedly write the same logic. Wave supports both condition-based and count-based looping, along with keywords to control flow during the loop.

This section explains how to use while and for loops, as well as the break and continue keywords, which control loop flow.

while loop​

The while loop repeatedly executes a block of code as long as the given condition evaluates to true. The loop terminates as soon as the condition becomes false.

This method is suitable for situations where the number of repetitions is unclear and you need to repeat until a specific condition is met.

Basic Structure​

The basic structure of the while loop in Wave is as follows.

while (condition) {
    // code to repeat
}

The condition must evaluate to a bool, and you can write one or more statements inside the code block enclosed in braces {}.

Example: Print numbers from 0 to 4​

var i :i32 = 0;

while (i < 5) {
    println("i is {}.", i);
    i = i + 1;
}

In this example, the loop runs as long as the variable i is less than 5. In each iteration, the current value is printed, and the value of i is incremented by 1 so that the condition eventually becomes false.

for loop​

The for loop is a type of loop suitable for use when the number of iterations is relatively clear. By defining the initial value, condition expression, and increment/decrement in one go, the flow of the loop can be clearly expressed.

Because all the elements needed to control the loop are gathered in one place, it is easy to understand the loop structure at a glance.

Basic Structure​

for (초기화; 조건식; 증감식) {
    // 반복할 코드
}

Wave의 for 초기화는 여러 형태를 지원합니다.

  • 암시적 var 타입 초기화
  • var / let mut / const 선언 초기화
  • 일반 식 초기화 (기존 변수 재사용)

예제 1: 암시적 타입 초기화​

for (i :i32 = 1; i <= 5; i += 1) {
    println("i = {}", i);
}

예제 2: var / let mut 초기화​

for (var i: i32 = 0; i < 3; i += 1) {
    println("var i = {}", i);
}

for (let mut j: i32 = 0; j < 3; j += 1) {
    println("let mut j = {}", j);
}

예제 3: 식 기반 초기화 (기존 변수 재사용)​

var i: i32 = 99;

for (i = 3; i <= 5; i += 1) {
    println("i = {}", i);
}

println("after loop: {}", i); // 6

선언형 초기화(var, let mut, i :i32 = ...)는 루프 스코프 변수로 동작하고,
식 기반 초기화(i = ...)는 바깥 변수 자체를 갱신합니다.

Nested Loops​

You can write a loop inside another loop, and this is called a nested loop. Nested loops are useful for iterating over two-dimensional data structures or handling combinations of multiple conditions.

Example: Double while loop​

var i :i32 = 0;

while (i < 3) {
    var j :i32 = 0;

    while (j < 2) {
        println("i={}, j={}", i, j);
        j = j + 1;
    }

    i = i + 1;
}

In this example, each time the outer while loop runs, the inner while loop runs completely. This allows sequential processing of combinations in the form of (i, j).

break Statement​

The break statement immediately terminates the loop and transfers control outside the loop. It is used when there is no need to continue the loop further.

Example: Exit loop at a specific value​

var i :i32 = 0;

while (true) {
    if (i == 5) {
        break;
    }

    println(i);
    i = i + 1;
}

In this example, within an infinite loop, when i becomes 5, break is executed, terminating the loop. In this way, the break statement is useful when you want to control the loop independently of its condition.

continue Statement​

The continue statement skips the remaining code in the current iteration and starts the next iteration immediately. It is used when you want to skip certain logic under specific conditions.

Example: Print only even numbers​

for (var i: i32 = 0; i <= 10; i = i + 1) {
    if (i % 2 == 1) {
        continue;
    }

    println(i);
}

In this code, if i is odd, continue is executed, skipping the print section. As a result, only even values are printed.

Summary​

Loops in Wave are designed to naturally express both condition-based and count-based iterations. The while loop is suitable for condition-centric repetition, while the for loop is useful when the iteration count and flow are clear.

By using break and continue together, you can finely control the execution flow even during iteration, allowing you to construct more sophisticated and flexible loop logic.