Programming Flix

bug! and unreachable!

Flix supports two special "functions": bug! and unreachable! that can be used to indicate when an internal program invariant is broken and execute should abort. For example:

match o {
    case Some(x) => ...
    case None    => bug!("The value of `o` cannot be empty.")
}

As another example:

match k {
    case n if n == 0 => ...
    case n if n >= 0 => ...
    case n if n <= 0 => ...
    case n           =>  unreachable!()
}

Use of bug! and unreachable! should be avoided whenever possible.