Loop and Break

With the loop expression, the expressions in the loop block are repeated for every iteration of the loop.

The GIF below of the Fortnite Emote Clean Sweep is an example of how a loop works. The GIF plays to the end, then repeats from the beginning, and the player emoting is like the expressions in a loop block.

# GIF
    loop:
        DoCleanSweepEmote()

Like a GIF, a loop block will repeat forever unless instructed to do otherwise. This is called an infinite loop.

Infinite loops are not very useful in most cases since they will block progress for the program, so Verse provides a way to end and / or suspend.

• End: You can end a loop by exiting with either break or return.

• Suspend: You can suspend a loop if it's used in an async expression. See Concurrency Overview for more details.

It's also possible to do both in the same loop. In this example, the loop block repeats until the random number that's generated is less than twenty.

loop:
        # generate random number
        RandomNumber : int = GetRandomInt(0, 100)
        # check if random number is less than twenty
        if (RandomNumber < 20):
            # exit loop
            break

Syntactically, this is the same as:

expression0
    loop:
        expression-block
        if (test-arg-block):
            break
        expression-block
    expression2

Unlike some of the other control flow expressions, the loop expression returns void, so it may not be useful in cases where you want an expression to return a result. If the loop is inside a function, then it's possible to return a value with return, but this will exit not only out of the loop but also out of the function.

Nested Loop Expressions

You can nest one loop inside another loop. The first loop is sometimes called the outer loop, and the second loop is called the inner loop. When the break expression is executed in an inner loop, it only breaks out of the inner loop.

In the example below, the outer loop continues to expression3, then the if expression after the inner loop exits and can execute expression1 and the inner loop again.

expression0
    # outer loop
    loop:
        expression1
        # inner loop
        loop:
            expression2
            if (test-arg-block0):
                # exit inner loop
                break