#!perl -l
my %weights=(a=>1,b=>2,c=>3);

my $max=0;
my @values=map { my $range=[ $max, $max+$weights{$_}, $_ ]; 
                 $max+=$weights{$_}; $range } keys %weights;

foreach (1..100) {
	my $r=rand($max);
	$_->[0]<=$r and $r<$_->[1] and print $_->[-1]
		foreach @values;
}