Extract the coefficients of an exponential generating function as
a list of Integers. Since EGF is an instance of Species, the
idea is that labelled can be applied directly to an expression
of the Species DSL. In particular, labelled s !! n is the
number of labelled s-structures on an underlying set of size n
(note that labelled s is guaranteed to be an infinite list).
> take 10 $ labelled octopi
gives the number of labelled octopi on 0, 1, 2, 3, ... 9 elements.