macro_rules! impl_froms {
($e:ident: $($v:ident $(($($sv:ident),*))?),*) => {
$(
impl From<$v> for $e {
fn from(it: $v) -> $e {
$e::$v(it)
}
}
$($(
impl From<$sv> for $e {
fn from(it: $sv) -> $e {
$e::$v($v::$sv(it))
}
}
)*)?
)*
}
}