module Biocaml_accu:A datastructure (based on Hashtbl) to accumulate values.sig..end
    An Accu.t can be seen as a generalized histogram: values 
    are mapped to bins, and each bin has a corresponding value
    which may be its size or its contents depending on the need.
type ('a, 'b, 'c, 'd) t 
'instances are mapped to 'bins, 
    and the 'accumulated value for a 'bin is updated with an 
    'incrementval create : ?n:int ->
       'a -> ('b -> 'c) -> ('d -> 'a -> 'a) -> ('b, 'c, 'd, 'a) tcreate ~n e f op creates an accumulator, which maps instances to bins
    with f, uses e as a neutral element (that is the value associated to a 
    bin before any value has been added to it) and updates the value of a bin 
    with op. n is an estimation of the maximum number of bins.val add : ('a, 'b, 'c, 'd) t -> 'a -> 'c -> unitadd accu x y updates the value in accu for
    the bin of x by an increment yval enum : ('a, 'b, 'c, 'd) t -> ('b * 'd) Batteries.Enum.tval get : ('a, 'b, 'c, 'd) t -> 'b -> 'dget accu x returns the value associated to b in accu.type'acounter =('a, 'a, int, int) t
module Counter:sig..end
val counts : ('a -> 'b) -> 'a Batteries.Enum.t -> ('b * int) Batteries.Enum.t