Result Type

The Result(OkType, ErrType) type represents a value that is either success (Ok) or failure (Err).

Syntax

state Result(Ok, Err) {
    Ok(Ok),
    Err(Err)
}

Use Result(i32, str) for a function that returns either an integer or an error string.

Creating Results

craft parse(s: str) -> Result(i32, str) {
    check (s == 0) {
        send Err("null string");
    }
    // ... parse logic ...
    send Ok(42);
}

Pattern Matching with choose

choose parse(input) {
    Ok(value) => {
        print(value);
    }
    Err(msg) => {
        print(`Error: ${msg}`);
    }
}

Checked Arithmetic

The math module provides checked operations that return Result on overflow:

bring "std.math";

craft main() -> void {
    choose math.add_checked_i32(2_000_000_000, 2_000_000_000) {
        Ok(sum) => print(sum);
        Err(_) => print("Overflow!");
    }
    send;
}

Built-in Checked Functions

Function	Returns	On Overflow
math.add_checked_i32	Result(i32, i32)	Err(0)
math.sub_checked_i32	Result(i32, i32)	Err(0)
math.mul_checked_i32	Result(i32, i32)	Err(0)