On Wed, 8 Sep 2010, Gregory Crosswhite wrote:
ExceptionT is a different matter because it handles "fail" as an uncaught error and places no restrictions on the error type, so one could implement the same functionality as AbortT by using ExceptionalT and requiring the end result be a monadic value of type "ExceptionalT e m e", where the exception and result types are the same. However, I believe that it is better to have the AbortT functionality available as a separate simple library specialized for this purpose than to have its functionality buried inside a more general library that is really intended to be used for a different purpose.
If we get rid of the notion of an exception as being something bad, and instead consider an exception as being early exit for whatever reason, I see no problem. E.g. you may well use an exception to terminate a successful search, returning the search result as exception value.