Control Flow

Flint keeps control flow conventional.

Conditionals

Use if and else for branching:

if ready {
    return ok(())
} else {
    return err(Error.NotReady)
}

Loops

Flint currently supports while and loop as the stable loop forms:

mut i = 0
while i < 10 {
    i = i + 1
}

loop {
    break
}

while is the obvious bounded loop. loop is the obvious infinite loop.

The parser already accepts for i in 0..10, but range-based for lowering is still being finished. Until that lands end to end, the book treats while and loop as the supported control-flow loops.

Match

match handles tagged unions and structured branching:

match state {
    State.Idle => { return }
    State.Busy(job) => { return run(job) }
}

Use match when the shape of a value should drive control flow.

For the common “one pattern or fall back” case, Flint also supports if let:

if let Option.Some(job) = next_job() {
    run(job)
} else {
    return
}

Defer

defer schedules cleanup for function exit:

fn work(bus: spi.Bus) -> Result<(), Error> {
    let device = bus.init()?
    defer device.release()

    return ok(())
}

Deferred actions run in last-in, first-out order when the function returns.