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

Antoine Latter aslatter at gmail.com
Tue Dec 23 10:39:24 EST 2008

On Tue, Dec 23, 2008 at 12:53 AM, Luke Palmer <lrpalmer at gmail.com> wrote:
> On Mon, Dec 22, 2008 at 6:52 PM, Antoine Latter <aslatter at gmail.com> 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


More information about the Haskell-Cafe mailing list