5. Control Flow

Control flow is how a program decides what happens next.

Alef has four beginner-level control-flow tools:

if

Use if when there are two or more possible paths.


fn owner(priority) {
    if priority == "P0" {
        return "incident-lead"
    }
    return "support"
}

fn main() {
    println(owner("P0"))
}
Output 

incident-lead

Boolean operators use words:


fn route(queue, text) {
    if queue == "platform" and text.contains("timeout") {
        return "incident"
    }
    return "normal"
}

Read that condition as ordinary language:


if queue is platform and text contains timeout

if With else

Use else when both branches do real work.


fn message(blocked) {
    if blocked {
        return "needs attention"
    } else {
        return "moving"
    }
}

If the first branch returns, you can often skip else and keep the code flat.

for

Use for to walk through arrays.


fn main() {
    let tickets = ["TD-101", "TD-102", "TD-103"]

    for ticket in tickets {
        println(ticket)
    }
}
Output 

TD-101
TD-102
TD-103

Inside the loop, ticket is the current item.

while

Use while when you need to repeat until a condition becomes false.


fn main() {
    let retries = 0

    while retries < 3 {
        println("try {retries}")
        retries = retries + 1
    }
}

while loops must change something inside the loop. Otherwise they can run forever.

match

Use match when the shape of a value matters.


match result {
    Ok(value) => println(value),
    Err(error) => println("failed: {error}"),
}

match is most useful with:

Exercise

Write a function named sla:

Then call it from main.