Macro cmpchain::chain

macro_rules! chain {
    (@wrap [$($prev:tt)*] [$($cur:tt)+] <  $next:tt $($rest:tt)*) => { ... };
    (@wrap [$($prev:tt)*] [$($cur:tt)+] <= $next:tt $($rest:tt)*) => { ... };
    (@wrap [$($prev:tt)*] [$($cur:tt)+] >  $next:tt $($rest:tt)*) => { ... };
    (@wrap [$($prev:tt)*] [$($cur:tt)+] >= $next:tt $($rest:tt)*) => { ... };
    (@wrap [$($prev:tt)*] [$($cur:tt)+] == $next:tt $($rest:tt)*) => { ... };
    (@wrap [$($prev:tt)*] [$($cur:tt)+] != $next:tt $($rest:tt)*) => { ... };
    (@arg_err $op:tt) => { ... };
    (@wrap [$($a:tt)*] [$($b:tt)*] < ) => { ... };
    (@wrap [$($a:tt)*] [$($b:tt)*] <=) => { ... };
    (@wrap [$($a:tt)*] [$($b:tt)*] > ) => { ... };
    (@wrap [$($a:tt)*] [$($b:tt)*] >=) => { ... };
    (@wrap [$($a:tt)*] [$($b:tt)*] ==) => { ... };
    (@wrap [$($a:tt)*] [$($b:tt)*] !=) => { ... };
    (@wrap [$($prev:tt)*] [$($cur:tt)+]) => { ... };
    (@wrap [$($prev:tt)*] [$($cur:tt)+] $next:tt $($rest:tt)*) => { ... };
    (@op $a:tt $op:tt $b:tt) => { ... };
    (@op $a:tt $op:tt $b:tt $($rest:tt)+) => { ... };
    (@op $($rest:tt)*) => { ... };
    (<  $($rest:tt)*) => { ... };
    (<= $($rest:tt)*) => { ... };
    (>  $($rest:tt)*) => { ... };
    (>= $($rest:tt)*) => { ... };
    (== $($rest:tt)*) => { ... };
    (!= $($rest:tt)*) => { ... };
    ($first:tt $($rest:tt)*) => { ... };
}

Succintly chain comparison operators like in Python and Julia.

chain! allows you to write comparisons that need to be simultaneously true more concisely. Instead of writing a < b && b < c, you can just write chain!(a < b < c). chain! has the added benefit that each argument is only evaluated once, rather than being evaluated for both the left and right comparisons. Arguments are lazily evaluated from left to right so that any arguments after the first failing comparison are not evaluated. chain! supports the comparison operators <, <=, >, >=, ==, != in any order.

Examples

// Check if a value falls between two bounds
let x = 8;
if chain!(4 < x <= 10) {
    assert!(true);
    // ...
}

// Check for equality of multiple values
assert!(chain!(4 == 2 * 2 == 12 / 3));