val create : ('a * float) list ‑> 'a tcreate dist compiles a discrete probability distribution into a form
supporting constant-time sampling. The running time is O(N) where N =
List.length dist. dist may be either a probability distribution
(all floats are non-negative and sum to 1) or, more generally,
a histogram in which frequencies are interpreted as probabilities.
val sample : ?state:Core.Random.State.t ‑> 'a t ‑> 'arandomly sample the distribution in constant time