Re: [Haskell-cafe] Stupid question #374: why is MaybeT not in the standard library?

On Tue, Dec 23, 2008 at 12:53 AM, Luke Palmer wrote:

On Mon, Dec 22, 2008 at 6:52 PM, Antoine Latter wrote:

...

Although I still had to use my own because I wanted a MonadPlus instance. I would offer a patch, but since there's more than one useful MonadPlus instance for MaybeT it probably still wouldn't be right for everyone.

There are? The only two I can think of are the left-biased and its dual, in which case the convention is to choose the left-biased one. Is there another?

It's a monad-transformer, so the MonadPlus/Alternative instance could either apply Maybe semantics or lift the behavior of whatever it wraps. -Antoine