If you look at the output below, the while loop is entered ('a') just one at the top.

The map is entered ('b') just 6 times as required.

If you look at the bottom, of the output, 'just' the required values are returned.

There is just the minor irritation of the weirdness marked '#??'.

sub a{
    my $x = shift;

    while(1){
        print 'a';
        map {
            print 'b';
            last if $_ == $x;
            $_;
        } @_;
        print 'c';
    };
}

my @data = 0 .. 9;

print for a( 5, @data );

__END__
c:\test>junk
a
b
b
b
b
b
b
0 ##??
1 ##??
2 ##??
3 ##??
4 ##??
5 ##??
6 ##??
7 ##??
8 ##??
9 ##??
0
1
2
3
4
[download]

I guess I was hoping for some of the legendary PM inventiveness?