Control Flow

If / Else

if is an expression — it produces a value:

let max = if a > b { a } else { b }

Multi-branch:

if score >= 90 {
    print("A")
} else if score >= 80 {
    print("B")
} else if score >= 70 {
    print("C")
} else {
    print("F")
}

For Loops

Iterate over collections:

for item in [1, 2, 3] {
    print(item)
}

With index:

for (i, item) in list.enumerate() {
    print("{i}: {item}")
}

Range-based:

for i in 0..10 {
    print(i)  // 0 through 9
}

for i in 0..=10 {
    print(i)  // 0 through 10 (inclusive)
}

While Loops

let mut count = 0
while count < 10 {
    print(count)
    count = count + 1
}

Loop (Infinite)

loop {
    let input = read_line()
    if input == "quit" {
        break
    }
    print("You said: " + input)
}

Break and Continue

for i in 0..100 {
    if i % 2 == 0 {
        continue  // skip even numbers
    }
    if i > 10 {
        break  // stop after 10
    }
    print(i)
}

Match Expressions

Pattern matching is one of Zap’s most powerful features:

match value {
    0 => print("zero"),
    1 | 2 | 3 => print("small"),
    n if n < 0 => print("negative"),
    _ => print("other"),
}

Destructuring in Match

match shape {
    Shape.Circle(r) => 3.14159 * r * r,
    Shape.Rectangle(w, h) => w * h,
    Shape.Triangle(a, b, c) => {
        let s = (a + b + c) / 2.0
        sqrt(s * (s - a) * (s - b) * (s - c))
    },
}

Match on Option

match find_user(id) {
    Some(user) => print("Found: " + user.name),
    None => print("User not found"),
}

Next Steps

Learn about the module system to organise larger programs.