module Exn_string:The point of this module is to be able to include an exn in a type that has to be sexpable or binable. Thesig
..end
Exn_string.t
type is more descriptive than just converting
to a string and is guaranteed to have come from an exn (unless someone abuses the
t_of_sexp
function or something).typet = private
string
include Sexpable
include Stringable
include Binable
val of_exn : exn -> t