Function try_from_raw_reprs 

fn try_from_raw_reprs<'a, E, R: TryFrom<RawRepr, Error = FromRawReprError<E>>>(
    r: impl IntoIterator<Item = &'a Spanned<RawRepr>>,
) -> Result<Option<Spanned<R>>, Spanned<FromRawReprsError<E>>>

Tries to extract a high-level repr from a list of RawReprs.