If

if is the only conditional in Strict. It comes in three forms: the block if, the single-line then … else, and the selector if, which works like switch or match in other languages. Like everything in Strict, all three are expressions and have a value.

Block if

if value > 0
    value

The condition is any Boolean expression, and the block below it is indented with one more tab. else and else if are optional:

if value is "("
    parentheses = parentheses.Increment
else if value is ")"
    parentheses = parentheses.Decrement
else if parentheses is 0
    value

An if often leaves a method early with return. From Examples/FizzBuzz.strict:

Classify Text
    FizzBuzz(3).Classify is "Fizz"
    FizzBuzz(5).Classify is "Buzz"
    FizzBuzz(15).Classify is "FizzBuzz"
    FizzBuzz(7).Classify is "7"
    if number % 15 is 0
        return "FizzBuzz"
    if number % 3 is 0
        return "Fizz"
    if number % 5 is 0
        return "Buzz"
    number to Text

When an if with an else is the last line of a method, the value of the branch that runs is the result. No return is needed:

AddIfEven(current Number, next Number) Number
    EvenFibonacci(100).AddIfEven(2, 4) is 6
    EvenFibonacci(100).AddIfEven(2, 3) is 2
    if next % 2 is 0
        current + next
    else
        current

Inside a for loop, an if without else filters values, see For.

Single-line then … else

A single-line conditional is used to return or assign a simple value based on a condition. It works like ?: in C, C# or Java, but uses then and else like F#, Scala or Haskell. It must fit in one line.

value > 0 then value else 0

C#:

var result = value > 0 ? value : 0;

Scala or Haskell:

val result = if value > 0 then value else 0

Conditionals can be chained. From Number.strict:

Clamp(minimum = 0, maximum = 1) Number
    1.7.Clamp(0.5, 1.5) is 1.5
    0.3.Clamp is 0.3
    -0.8.Clamp(-0.5, 0.5) is -0.5
    value > maximum then maximum else value < minimum then minimum else value

A conditional that is one of several arguments needs brackets: Text(value, (isShort then 2 else 4)).

Selector if

The selector if starts like a block if, but the if line ends with is (or is not). Each line below it is a case with a value and then. It works like switch or match in other languages, but it is more powerful: a case can be any expression, any arithmetic or comparison, or a type check. From Examples/ArithmeticFunction.strict:

has first Number
has second Number
Calculate(operation Text) Number
    ArithmeticFunction(10, 5).Calculate("add") is 15
    ArithmeticFunction(10, 5).Calculate("subtract") is 5
    ArithmeticFunction(10, 5).Calculate("multiply") is 50
    if operation is
        "add" then first + second
        "subtract" then first - second
        "multiply" then first * second
        "divide" then first / second

The same in other languages:

var result = operation switch
{
    "add" => first + second,
    "subtract" => first - second,
    "multiply" => first * second,
    "divide" => first / second,
    _ => throw new InvalidOperationException("Unknown operation: " + operation)
};

val result = operation match
    case "add" => first + second
    case "subtract" => first - second
    case "multiply" => first * second
    case "divide" => first / second
    case _ => "Unknown operation"

let result = case operation of
    "add" -> first + second
    "subtract" -> first - second
    "multiply" -> first * second
    "divide" -> first / second
    _ -> "Unknown operation: " ++ operation

The last line can be an else case:

Name Text
    Count(1).Name is "one"
    Count(5).Name is "many"
    if number is
        1 then "one"
        2 then "two"
        else "many"

If there is no else case and no case matches, an Error is created and thrown automatically at runtime. You don't need to write a default case that throws, like the C# _ => throw above.

Cases can also check types. From HashCode.strict:

from(generic)
    HashCode(5) is 5
    HashCode("abc") is 3
    HashCode((1, 2)) is 2
    if generic is
        Number then generic
        Iterator then generic.Length
        else 0

Like any if, a selector if can be the body of a for loop, where value is the current element, see For.