Freq is a trivial Haskell library for computing frequencies of integers and the distribution of combinatorial statistics. As illustrated by the following ghci session you can, for instance, easliy compute the distribution of descents over all permutations of any given (small) length:

> :m +Math.Freq 
> let des xs = sum [ 1 | (x,y) <- zip xs (tail xs), x > y ]
> mapM_ (print . dist des . permutations . enumFromTo 1) [1..5]
[1]
[1,1]
[1,4,1]
[1,11,11,1]
[1,26,66,26,1]