Binary search

With either of the below implementations of binary_search, one could write a function to search any object that does Positional this way:

sub search (@a, $x --> Int) {
    binary_search { $x cmp @a[$^i] }, 0, @a.end
}

Iterative

sub binary_search (&p, Int $lo is copy, Int $hi is copy --> Int) {
    until $lo > $hi {
        my Int $mid = ($lo + $hi) div 2;
        given p $mid {
            when -1 { $hi = $mid - 1; } 
            when  1 { $lo = $mid + 1; }
            default { return $mid;    }
        }
    }
    fail;
}

Recursive

sub binary_search (&p, Int $lo, Int $hi --> Int) {
    $lo <= $hi or fail;
    my Int $mid = ($lo + $hi) div 2;
    given p $mid {
        when -1 { binary_search &p, $lo,      $mid - 1 } 
        when  1 { binary_search &p, $mid + 1, $hi      }
        default { $mid                                 }
    }
}