@return

@return ends a macro and, optionally, gives a value back to the caller.

Syntax

@return value
@return

Example

macro clamp(x: int, lo: int, hi: int) -> int {
    @if x < lo {
        @return lo
    }
    @if x > hi {
        @return hi
    }
    @return x
}

macro show(value: int) {
    @emit value
}

show clamp(-5, 0, 10)
show clamp(50, 0, 10)
show clamp(7, 0, 10)

0 10 7

Details

• @return stops the macro at once, even from inside @if, @match, @for or @fold.
• A bare @return ends the macro without a value.
• Values the macro emitted before returning stay emitted.
• @return f(...), where f is the macro itself, is a tail call: it doesn’t count toward the recursion limit. See Recursion.
• @return can return the value of a call that emits, and its emitted values are kept. See Returning values.

Returning early

macro first_multiple_of(k: int, limit: int) -> int {
    @for i in 1..limit {
        @if i % k == 0 {
            @return i
        }
    }
    @return -1
}

macro show(value: int) {
    @emit value
}

show first_multiple_of(7, 100)
show first_multiple_of(700, 100)

7 -1