Runtime Errors

There are three different methods of raising errors at runtime. The first one is just to panic, which doesn’t really count, so we’ll skip past that one!

Unrecoverable errors

Using an ordinary Result as the return type of your function will raise the error immediatly within the VM if the error case is hit.

// rust
#[mimas]
fn oops() -> Result<(), RtErr> {
    Err(RtErr::Custom("oops!"));
}

// mimas
oops(); // runtime error: oops!

The standard library avoids using these in favor of relying on the type system or handing back raisable errors, but hey, you do you.

Raisable errors

To return an actual mimas Result, you use Raisable.

// rust
#[mimas]
fn test(b: bool) -> Raisable<()> {
    if b {
        Raisable::Ok(())
    } else {
        Raisable::Raised("not true!");
    }
}

// mimas
test(false) absolve |e| print(e); // > not true!

Raisable has a blanket implementation on Result<T, E> (so long as E is Display).

#[mimas]
fn load_file(path: &str) -> Raisable<String> {
    std::fs::read_to_string(path).into()
}