Control flow

if/elif/else, while, for, loop, break/continue, labeled loops, and break-with-value.

Summary

Braces are always required. if is an expression and returns the taken branch value. for iterates over arrays, ranges, strings, and maps (yielding key-value tuples when destructured). loop runs forever until break; break val makes the loop expression return that value. Labeled loops let you break outer or continue outer from a nested loop.

Canonical

If / Elif / Else

if x > 0 {
    println("positive")
} elif x < 0 {
    println("negative")
} else {
    println("zero")
}

Braces are always required.

if works as an expression: it returns the value of the taken branch:

let sign = if x > 0 { "+" } else { "-" }

While Loop

var i = 0
while i < 10 {
    println(i)
    i = i + 1
}

For Loop

-- over array
for x in [1, 2, 3] {
    println(x)
}

-- over range (exclusive)
for i in 0..5 {
    println(i)                   -- 0, 1, 2, 3, 4
}

-- over range (inclusive)
for i in 1..=3 {
    println(i)                   -- 1, 2, 3
}

-- over string characters
for ch in "hello".chars() {
    print(ch)
}

-- over map (iterates keys)
let m = #{"a": 1, "b": 2}
for k in m {
    println("{k}: {m[k]}")
}

-- over map key-value pairs (direct destructuring)
for (k, v) in m {
    println("{k} = {v}")
}

-- .entries() also works
for (k, v) in m.entries() {
    println("{k} = {v}")
}

Loop (Infinite)

var n = 0
loop {
    n = n + 1
    if n >= 10 { break }
}

Break and Continue

for i in 0..100 {
    if i % 2 == 0 { continue }  -- skip even numbers
    if i > 20 { break }         -- stop at 20
    println(i)
}

Break with Value

loop can return a value via break:

let result = loop {
    break 42
}
println(result)                  -- 42

Labeled Loops

Break or continue an outer loop from an inner one.

outer: for i in range(5) {
    for j in range(5) {
        if i * j == 6 {
            break outer          -- breaks the outer loop
        }
    }
}

outer2: for i in range(3) {
    for j in range(3) {
        if j == 1 { continue outer2 }  -- skips to next i
    }
}

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