An interpretation of species as exponential generating functions, which count labelled structures.
Extract the coefficients of an exponential generating function as
a list of
EGF is an instance of
idea is that
labelled can be applied directly to an expression
of the species DSL. In particular,
number of labelled
s-structures on an underlying set of size
is guaranteed to be an infinite list).
> take 10 $ labelled octopi [0,1,3,14,90,744,7560,91440,1285200,20603520]
gives the number of labelled octopi on 0, 1, 2, 3, ... 9 labels.