#[macro_export]
macro_rules! iff {
(let $pat:pat = $expr:expr, $($tt:tt)+) => {
if let $pat = $expr {
iff!($($tt)+)
}
};
(let $pat:pat = $expr:expr => $block:block) => {
if let $pat = $expr {
$block
}
};
($expr:expr, $($tt:tt)+) => {
if $expr {
iff!($($tt)+)
}
};
($expr:expr => $block:block) => {
if $expr {
$block
}
};
}