Control flow

Iona provides a number of control flow structures that make it easy to write understandable and concise code. From if else over when to guard statements and ultimately for and while loops.

Conditional Statements

If else

Iona allows the traditional if/else if/else branches like most other c-based languages:

if value == 1 {
    ...
} else if value == 2 {
    ...
} else {
    ...
}

Unlike some other languages, they can be expressions and not just statements as well:

var data = if value == 1 {
    1
} else if value == 2 {
    2
} else {
    3
}

warning

If else can only be used as an expression if every branch only has a single expression.

This doesn't work:

var data = if value == 1 {
    var user = 3
    user
} else if value == 2 {
    2
} else {
    3
}

When

Iona comes with a keyword different to most other languages. When behaves like switch but comes with a few extras. Instead of having multiple case, and sometimes a default, cases, it provides are more intuitive approach. Cases can be ranges or values, not just values:

when value {
    0...3 -> ...
    4 -> ...
} else {
    ...
}

Note how the first case is a range from 0-3 and the second case is just 4.

Additionally, Instead of a default case, Iona introduces the else branch for when, making code more intuitive to read and write.

when also works with conditions:

var str = String("Foo")

when str {
    str == "Foo" -> ...
    str != "Foo" -> ...
}

note

There is no implicit fallthrough in Iona for when. If multiple cases are supposed to do the same, they can be written like this:

when str {
    "Foo", "foo" -> ...
} else {
    ...
}

Alternatively the next keyword indicates that the current case should be ended and the next one shall be executed:

when str {
    "Foo" -> next
    "foo" -> ...
} else {
    ...
}

Loops

For loops

Unlike other languages, Iona only has a single for loop. There is no separate for, for-in, and for-each loop. for is used for all of these scenarios.

Iterating over a range:

for x in 0...3 {
    ...
}

if the index in range-based loop is not needed, it can be discarded by using _:

for _ in 0...3 {
    ...
}

Iterating over the elements of an array:

var items: [Int] = [1, 2, 3]

for item in items {
    ...
}

While loops

While loops repeat their body until the condition of the loop's head is no longer fulfilled:

var isLoggedIn = true

while isLoggedIn {
    ...
}

While loops also come with their cousin, do-while. Do-while behaves exactly the same, just that the condition is evaluated after each run, which means a do-while loop always runs at least once:

var isLoggedIn = true

do {
    ...
} while isLoggedIn

tip

You can end the current iteration of every loop with the keyword continue:

while foo {
    if bar {
        continue
    }
}