Re: Functor => Pointed => Applicative => Monad

From: David Menendez Subject: Re: Functor => Pointed => Applicative => Monad To: Isaac Dupree Cc: libraries@haskell.org Message-ID: Content-Type: text/plain; charset=ISO-8859-1

On Mon, Nov 29, 2010 at 11:26 AM, Isaac Dupree wrote:

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On 11/29/10 03:39, John Smith wrote:

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Is there any intention to reorganise the standard class hierarchy, arranging them logically instead of in order of invention? I plagiarised the following example from http://stackoverflow.com/questions/1634911/can-liftm-differ-from-lifta and Trac:

class Functor f where map :: (a -> b) -> f a -> f b

class Functor f => Pointed f where pure :: a -> f a

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.

It's useful for 'singleton' on probabilistic data structures (e.g. a Bloom filter). John