Sorry for the confusion! I meant 'unsafe' as in partial (not safe for all inputs). Not as in Rust's unsafe keyword.

Ah, right. It's really important in the context of Rust. :) People sometimes claim that unwrap() violates memory safety, which isn't true.

The definition in Rust's documentation[0] was this:

    let x: Option<&str> = None;
    assert_eq!(x.unwrap(), "air"); // fails

The equivalent Haskell if unwrap throws a panic as the docs[0] seem to imply:

    λ> fromMaybe (error "panic!") Nothing
    *** Exception: panic!

You could also do something like this if you don't mind dealing with the wrapped boolean value:

    λ> fmap (== "air") (Just "air")
    Just True

and the failure case:

    λ> fmap (== "air") (Nothing)
    Nothing 

0: https://doc.rust-lang.org/std/option/enum.Option.html#method...

Right, but it's still not unsafe. The stack unwinds, destructors get called.

And I meant some notion of 'safety', not fromMaybe/fromJust.