fn main() {
    println!("{:?}", get_number());
}

enum InternalErrorType {
    DidNotProduceValidNumber
}

#[derive(Debug)]
enum OutwardsErrorType {
    SomethingWentWrongPleaseRetry
}

fn get_number() -> Result<u32, OutwardsErrorType> {
    let number = internal_get_interesting_number()?;
    // do interesting operations
    Ok(number)
}

fn internal_get_interesting_number() -> Result<u32, InternalErrorType> {
    Err(InternalErrorType::DidNotProduceValidNumber)
}

impl From<InternalErrorType> for OutwardsErrorType {
    fn from(internal_error: InternalErrorType) -> OutwardsErrorType {
        match internal_error {
            InternalErrorType::DidNotProduceValidNumber => OutwardsErrorType::SomethingWentWrongPleaseRetry
        }
    }
}