Asynchronous exceptions can occur during the construction of a lazy data structure. They are represented by a lazy data structure itself.

This module re-exports the type with lazy combinators.

TODO:

• Is the Null type appropriate anywhere? Should it be better a Monoid type with mempty? Shall Monoid.mempty be the default, or functions with explicit default values?
• Shall we replace Monad constraint by Functor constraint, where we only need liftM?