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Control Flow

Control flow is used to change the behavior of the program based on certain conditions. This is known as branching.

If Expression​

You can use an if expression to execute different blocks of code based on a condition.

For example:

let size = if number > 100 {
    "large"
} else {
    "small"
};

It's worth noting that this will only execute the branch that matches the condition. This means that you can use a type guard to narrow the type of variables after the condition is evaluated.

However, if you don't need to narrow the type, you can use an inline if expression to immediately execute both branches and return the result of the branch that matches the condition. This can be an important optimization to reduce the size of the compiled program, but it can also lead to logic errors or higher runtime costs if you're not careful.

The example above is a great example of when you should use an inline if expression:

let size = inline if number > 100 {
    "large"
} else {
    "small"
};

If Statement​

To reduce the amount of indentation, you can use an if statement instead of an if expression if you're going to exit the function early if the condition is met (i.e., an early return).

This might look like this:

if list is nil {
    return 0;
}

let (first, rest) = list;

Raise​

You can use a raise statement to immediately exit the program with an error.

raise "List is empty";

This will cause the program to fail with the message "List is empty".

info

In release builds, error messages will automatically be omitted to reduce the size of the compiled program.

Assert​

The assert statement is a shorthand for raise inside of an if statement:

assert !(list is nil);

It's useful for checking types at runtime and raising an error if the condition is not met.

Return​

You can use a return statement to exit the current function early and return a value.

return 0;