Matches one condition against a single fact, independently of any token.
:fun is arity 1, (fact) -> bindings_map | nil. It matches a fact of
any type on purpose: which alpha nodes a fact reaches is decided by
Rete.Taxonomy's type index, so that derive(:premium, :customer) lets a
:premium fact reach a condition written against :customer.
Summary
Types
@type t() :: %Rete.Network.Node.Alpha{ code: atom(), fun: fun(), id: non_neg_integer() | nil, type: atom() }