Control Flow

Control flow statements direct the order of execution based on conditions.

If Statements

The if statement executes a block of code when a condition is truthy.

if temperature > 100 {
    say "boiling"
}

The condition is any expression. It is evaluated using Forge’s truthiness rules: false and null are falsy, everything else is truthy.

If-Else

An else clause provides an alternative block when the condition is falsy. Forge supports three equivalent keywords for the else clause:

Classic: else

if age >= 18 {
    say "adult"
} else {
    say "minor"
}

Natural: otherwise

if age >= 18 {
    say "adult"
} otherwise {
    say "minor"
}

Casual: nah

if age >= 18 {
    say "adult"
} nah {
    say "minor"
}

All three forms are semantically identical. The else block executes when the condition is falsy.

If-Else If Chains

Multiple conditions can be tested in sequence using else if (or otherwise if / nah if):

if score >= 90 {
    say "A"
} else if score >= 80 {
    say "B"
} else if score >= 70 {
    say "C"
} else {
    say "F"
}

Conditions are tested top to bottom. The first truthy condition’s block is executed. If no condition is truthy and an else clause is present, its block executes.

Nested If Statements

If statements can be nested arbitrarily:

if user != null {
    if user.role == "admin" {
        say "admin access"
    } else {
        say "regular access"
    }
} else {
    say "not logged in"
}

Block Scoping

Variables declared inside an if or else block are scoped to that block:

if true {
    let msg = "inside"
    say msg     // "inside"
}
// msg is not accessible here

No Ternary Operator

Forge does not have a ternary conditional operator (condition ? a : b). Use an if-else statement or a when expression instead:

// Using when as a conditional expression
let label = when age {
    >= 18 -> "adult",
    else -> "minor"
}

If as a Statement

if is always a statement in Forge. It does not produce a value that can be used in expression position. To select between values conditionally, use a when expression.

Truthiness in Conditions

The condition in an if statement follows Forge’s truthiness rules:

if 0 {
    say "zero is truthy"        // this executes
}

if "" {
    say "empty string is truthy"    // this executes
}

if null {
    say "unreachable"
} else {
    say "null is falsy"         // this executes
}

if false {
    say "unreachable"
} else {
    say "false is falsy"        // this executes
}

See Truthiness Rules for the complete specification.