Control Flow ​

If ​

The syntax for if expressions is if condition {} or if condition: expression. It is also possible to have an else branch, for example if condition: expression1 else expression2. The if expression gets the value of the evaluated branch.

let result = if x < 5 {
    x + 1
} else {
    -1
}
let result = if x < 5: x + 1 else -1

let result = if x < 5 {
    x + 1
} else {
    -1
}
let result = if x < 5: x + 1 else -1

Postfix If ​

A postfix if is used to evaluate an expression only if a condition is true. The syntax for this is expression if condition.

echo(x) if x > 0

echo(x) if x > 0

Nil Coalescing ​

With the nil coalescing operator, the right hand side is used if the left hand side is nil.

nil ?? 5     #=> 5
"hello" ?? 5 #=> "hello"
"" ?? 5      #=> ""

nil ?? 5     #=> 5
"hello" ?? 5 #=> "hello"
"" ?? 5      #=> ""

Loops ​

While ​

A while loop evaluates its branch repeatedly for as long as the given condition is true, with the syntax while condition {} or while condition: expression.

while x > 0 {
    x -= 1
}

while x > 0: x -= 1

while x > 0 {
    x -= 1
}

while x > 0: x -= 1

For ​

A for loop iterates over an iterable value and has the syntax for itemName in value {} or for itemName in value: expression where itemNameis a user-chosen name for the variable created each iteration. It is also possible to specify multiple variable names here if the value is a tuple.

for item in [1, 2, 3]: echo(item)
for item, i in [1, 2, 3] | withIndex: echo("${i}: ${item}")
for i in 0..10: echo(i)

for item in [1, 2, 3]: echo(item)
for item, i in [1, 2, 3] | withIndex: echo("${i}: ${item}")
for i in 0..10: echo(i)

Break and Continue ​

A loop can be stopped at any time using the break keyword. When an expression is put after a breakkeyword, the loop expression itself gets the value of this expression. It is also possible to immediately skip to the next iteration using the continue keyword.

# result is going to be either 123 or nil
let result = while x > 0 {
    break 123 if x == 2
    x -= random(1, 3)
}

# result is going to be either 123 or nil
let result = while x > 0 {
    break 123 if x == 2
    x -= random(1, 3)
}