distributive (empty) → 0.1

raw patch · 4 files changed

+147/−0 lines, 4 filesdep +basedep +transformerssetup-changed

Dependencies added: base, transformers

Files

• Data/Distributive.hs +82/−0
• LICENSE +30/−0
• Setup.lhs +7/−0
• distributive.cabal +28/−0

@@ -0,0 +1,82 @@+-----------------------------------------------------------------------------+-- |+-- Module      :  Data.Distributive+-- Copyright   :  (C) 2011 Edward Kmett+-- License     :  BSD-style (see the file LICENSE)+--+-- Maintainer  :  Edward Kmett <ekmett@gmail.com>+-- Stability   :  provisional+-- Portability :  portable+--+----------------------------------------------------------------------------+module Data.Distributive +  ( Distributive(..)+  , fmapDefault+  , cotraverse+  , comapM+  ) where++import Control.Applicative+import Control.Monad (liftM)+import Control.Monad.Trans.Identity+import Control.Monad.Trans.Reader+import Control.Monad.Instances ()+import Data.Functor.Identity++-- | This is the categorical dual of 'Traversable'. However, there appears+-- to be little benefit to allow the distribution via an arbitrary comonad+-- so we restrict ourselves to 'Functor'.+-- +-- Minimal complete definition: 'distribute' or 'collect'+--+-- To be distributable a container will need to have a way to consistently+-- zip a potentially infinite number of copies of itself. This effectively+-- means that the holes in all values of that type, must have the same +-- cardinality, fixed sized vectors, infinite streams, functions, etc.+-- and no extra information to try to merge together.++class Functor g => Distributive g where+  -- | The dual of 'Data.Traversable.sequence'+  -- +  -- > distribute = collect id+  distribute  :: Functor f => f (g a) -> g (f a)+  distribute  = collect id++  -- | +  -- > collect   = distribute . fmap f+  collect     :: Functor f => (a -> g b) -> f a -> g (f b)+  collect f   = distribute . fmap f++  -- | +  -- > distributeM = fmap unwrapMonad . distribute . WrapMonad+  distributeM :: Monad m => m (g a) -> g (m a)+  distributeM = fmap unwrapMonad . distribute . WrapMonad ++  -- | +  -- > collectM = distributeM . liftM f+  collectM    :: Monad m => (a -> g b) -> m a -> g (m b)+  collectM f  = distributeM . liftM f++cotraverse :: (Functor f, Distributive g) => (f a -> b) -> f (g a) -> g b+cotraverse f = fmap f . distribute++comapM :: (Monad m, Distributive g) => (m a -> b) -> m (g a) -> g b+comapM f = fmap f . distributeM++instance Distributive Identity where+  collect f = Identity . fmap (runIdentity . f)+  distribute = Identity . fmap runIdentity++instance Distributive ((->)e) where+  distribute a e = fmap ($e) a++instance Distributive g => Distributive (ReaderT e g) where+  distribute a = ReaderT $ \e -> collect (flip runReaderT e) a++instance Distributive g => Distributive (IdentityT g) where+  collect f = IdentityT . collect (runIdentityT . f)++-- | Every 'Distributive' is a 'Functor'. This is a valid default definition.+fmapDefault :: Distributive g => (a -> b) -> g a -> g b+fmapDefault f = cotraverse (f . runIdentity) . Identity+

@@ -0,0 +1,30 @@+Copyright 2011 Edward Kmett++All rights reserved.++Redistribution and use in source and binary forms, with or without+modification, are permitted provided that the following conditions+are met:++1. Redistributions of source code must retain the above copyright+   notice, this list of conditions and the following disclaimer.++2. Redistributions in binary form must reproduce the above copyright+   notice, this list of conditions and the following disclaimer in the+   documentation and/or other materials provided with the distribution.++3. Neither the name of the author nor the names of his contributors+   may be used to endorse or promote products derived from this software+   without specific prior written permission.++THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR+IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE+DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE FOR+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS+OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)+HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,+STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN+ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE+POSSIBILITY OF SUCH DAMAGE.

@@ -0,0 +1,7 @@+#!/usr/bin/runhaskell+> module Main (main) where++> import Distribution.Simple++> main :: IO ()+> main = defaultMain

@@ -0,0 +1,28 @@+name:          distributive+category:      Data Structures+version:       0.1+license:       BSD3+cabal-version: >= 1.6+license-file:  LICENSE+author:        Edward A. Kmett+maintainer:    Edward A. Kmett <ekmett@gmail.com>+stability:     provisional+homepage:      http://github.com/ekmett/distributive/+copyright:     Copyright (C) 2011 Edward A. Kmett+synopsis:      Haskell 98 Distributive functors -- Dual to Traversable+description:   Haskell 98 Distributive functors -- Dual to Traversable+build-type:    Simple++source-repository head+  type: git+  location: git://github.com/ekmett/distributive.git++library+  build-depends: +    base >= 4 && < 4.4,+    transformers >= 0.2.0 && < 0.3++  exposed-modules:+    Data.Distributive++  ghc-options: -Wall