Function fallible_func_device 

pub fn fallible_func_device<F, B, T, E>(
    forward: F,
    backward: B,
) -> impl Device<Error = E>
where
    F: FnMut() -> Result<T, E>,
    B: FnMut() -> Result<T, E>,

A device which uses callbacks which may fail.

See func_device() for a version which uses infallible callbacks.