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Control flow

Conditional statements

Conditional statements are used to execute code based on a condition. In Radon, the if statement is used to execute code if a condition is true. The else statement is used to execute code if the condition is false. The elif statement is used to execute code if the condition is false and another condition is true. The else statement is optional.

conditional-statements.rn
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if true {
    print("true")

} else {
    print("false")
}
conditional-statements.rn
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if true {
    print("true")

} elif false {
    print("false")

} else {
    print("neither")
}

Switch statement

The switch statement matches an expression against one or more case values. The first matching case runs; default runs when no case matches.

switch.rn
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fun describe(x) {
    switch x {
        case 1  -> print("one")
        case 2  -> print("two")
        case 3  -> print("three")
        default -> print("something else: " + str(x))
    }
}

describe(2)  # two
describe(99) # something else: 99

Multi-line case body

When a case body needs more than one statement, wrap it in { }:

switch-block.rn
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switch x {
    case 1 {
        print("one")
        print("still one")
    }
    default { print("not one") }
}

fallthrough

fallthrough causes execution to continue into the next case body without re-checking its condition:

fallthrough.rn
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for x in [1, 2, 3] {
    switch x {
        case 2 { fallthrough }
        case 3 { print("two or three") }
        default { print("other: " + str(x)) }
    }
}

fallout

fallout immediately exits the switch block, similar to break in a loop:

fallout.rn
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switch 44 {
    case 43 -> print("43")
    case 44 -> fallout           # stops here; cases below are skipped
    case 45 -> print("45")
    default -> print("default")
}

Assert statement

assert takes a condition and an optional message. If the condition is falsy the program raises an error with the message.

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assert true, "this never fires"

var x = 42
assert x > 0, "x must be positive"

assert can also be used as an expression — it returns the asserted value on success:

assert-expr.rn
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const y = assert 99, "must be truthy"
print(y) # 99

Catching a failed assertion:

assert-catch.rn
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try {
    assert false, "something went wrong"
} catch as e {
    print(e) # something went wrong
}

Del statement

del removes one or more variables from the current scope. Accessing a deleted name afterwards raises an error.

del.rn
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var a = 1
var b = 2
del a, b

try {
    print(a)
} catch as e {
    print(e) # 'a' is not defined
}

del also works on indexed targets:

del-index.rn
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var arr = [10, 20, 30]
del arr[1]
print(arr) # [10, 30]