mostly correct and complete &min implementation

min.pl

sub my-min(*@values, :&by = &infix:<cmp>) {
    my Mu $min;
    if &by.arity == 0|1 {
        my &transform := &by.arity == 0 ?? -> $x { by() } !! &by;
        my $min-return;
        $min = transform(@values[0]);
        for @values {
            # FIRST next;
            my $current := transform($_);
            if $current cmp $min < 0 {
                $min = $current;
                $min-return = $_;
            }
        }
        @values ?? $min-return !! -Inf;
    } else {
        my &cmp := &by.arity == 2 ?? &by !! { $^a cmp $^b };
        my Bool $is-initialized = False;
        for @values {
            if $is-initialized {
                $min = $_ if cmp($_, $min) < 0;
            } else {
                if .defined {
                    $min = $_;
                    $is-initialized = True;
                }
            }
        }
        $is-initialized ?? $min !! -Inf;
    }
}

say my-min(Any, Any);
say my-min();
say my-min(-3, 5, -8, 9);
say my-min(Any, -3, 5, -8, 9);
say my-min('ab', 'foo', 'bar', 'aa');
say my-min(1..20, :by(&rand));
say my-min(-3, 5, -8, 9, :by(&prefix:<->));