Functor => Pointed => Applicative => Monad

Henning Thielemann lemming at
Wed Dec 22 15:23:04 CET 2010

David Menendez wrote:
> On Mon, Nov 29, 2010 at 11:26 AM, Isaac Dupree
>> Is it useful to have Pointed non-Functors?
> Is Pointed useful at all? The last time this discussion came up, I
> asked for algorithms which were generic over pointed functors (in the
> same way that traverse is generic over applicative functors) and no
> one could think of any.

I remember that I have recently abused Applicative in connection with 
Traversable in order to get the 'pure' method.

First example: A general implementation of a 'peek' for traversable 

Second example: The liftPoint function in
that lifts a not-quite arrow (T a b) to a (T (t a) (t b)) where 't' is 

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