 Computation type:
 Computations which can be interrupted and resumed.
 Binding strategy:
 Binding a function to a monadic value creates
a new continuation which uses the function as the continuation of the monadic
computation.
 Useful for:
 Complex control structures, error handling,
and creating coroutines.
 Zero and plus:
 None.
 Example type:
 Cont r a
The Continuation monad represents computations in continuationpassing style
(CPS).
In continuationpassing style function result is not returned,
but instead is passed to another function,
received as a parameter (continuation).
Computations are built up from sequences
of nested continuations, terminated by a final continuation (often id)
which produces the final result.
Since continuations are functions which represent the future of a computation,
manipulation of the continuation functions can achieve complex manipulations
of the future of the computation,
such as interrupting a computation in the middle, aborting a portion
of a computation, restarting a computation, and interleaving execution of
computations.
The Continuation monad adapts CPS to the structure of a monad.
Before using the Continuation monad, be sure that you have
a firm understanding of continuationpassing style
and that continuations represent the best solution to your particular
design problem.
Many algorithms which require continuations in other languages do not require
them in Haskell, due to Haskell's lazy semantics.
Abuse of the Continuation monad can produce code that is impossible
to understand and maintain.
