cautious

Keep track of warnings and errors during calculations.

A Cautious monad "Monoid w => Cautious w e a" which keeps track of the success of a task. The options are "CautiousWarning w a" (where "CautiousWarning mempty a" represents "success") and "CautiousError e". In addition, there is a monadtransformer "Monad m, Monoid w => CautiousT w e m a"