Re (tilly) 1: (Golf as well): List of Partitions

[tilly]

Occasionally I wish I hadn't given away most of my math books, this is one of those occasions. I had a book with lots about partitions in it, but I long ago gave it away. However this problem is quite doable. The trick is to make P a function of 2 variables, first the number n you are interested in partitioning, and then the number i that is the largest number you are willing to partition it into.

With that tip, here is an answer in 90 characters:

sub P {
my($n,$i)=@_;$i||=$n;$i-1?map{my$c=$_;map[($i)x$c,@$_],P($n-$c*$i,$i-1
+)}0..$n/$i:[(1)
x$n]
}