contravariant 0.4 → 0.4.1

raw patch · 3 files changed

+200/−4 lines, 3 filesPVP ok

version bump matches the API change (PVP)

API changes (from Hackage documentation)

Files

• CHANGELOG.markdown +4/−0
• Data/Functor/Contravariant/Day.hs +191/−0
• contravariant.cabal +5/−4

@@ -1,3 +1,7 @@+0.4.1+-----+* Added `Day` convolution under `Data.Functor.Contravariant.Day`.+ 0.3 --- * Added `Backwards` and `Reverse` instances for `transformers` 0.3

@@ -0,0 +1,191 @@+{-# LANGUAGE CPP #-}+{-# LANGUAGE ExistentialQuantification #-}+{-# LANGUAGE Rank2Types #-}+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ > 707+{-# LANGUAGE DeriveDataTypeable #-}+#endif+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 707+{-# LANGUAGE KindSignatures #-}+#endif+-----------------------------------------------------------------------------+-- |+-- Copyright   :  (C) 2013 Edward Kmett, Gershom Bazerman and Derek Elkins+-- License     :  BSD-style (see the file LICENSE)+--+-- Maintainer  :  Edward Kmett <ekmett@gmail.com>+-- Stability   :  provisional+-- Portability :  portable+--+-- The Day convolution of two contravariant functors is a contravariant+-- functor.+--+-- <http://ncatlab.org/nlab/show/Day+convolution>+----------------------------------------------------------------------------++module Data.Functor.Contravariant.Day+  ( Day(..)+  , day+  , runDay+  , assoc, disassoc+  , swapped+  , intro1, intro2+  , day1, day2+  , diag+  , trans1, trans2+  ) where++import Control.Applicative+import Data.Functor.Contravariant+import Data.Proxy+import Data.Tuple (swap)+#ifdef __GLASGOW_HASKELL__+import Data.Typeable+#endif++-- | The Day convolution of two contravariant functors.+data Day f g a = forall b c. Day (f b) (g c) (a -> (b, c))+#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ > 707+  deriving Typeable+#endif++-- | Construct the Day convolution+--+-- @+-- 'day1' ('day' f g) = f+-- 'day2' ('day' f g) = g+-- @+day :: f a -> g b -> Day f g (a, b)+day fa gb = Day fa gb id++#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 707+instance (Typeable1 f, Typeable1 g) => Typeable1 (Day f g) where+    typeOf1 tfga = mkTyConApp dayTyCon [typeOf1 (fa tfga), typeOf1 (ga tfga)]+        where fa :: t f (g :: * -> *) a -> f a+              fa = undefined+              ga :: t (f :: * -> *) g a -> g a+              ga = undefined++dayTyCon :: TyCon+#if MIN_VERSION_base(4,4,0)+dayTyCon = mkTyCon3 "contravariant" "Data.Functor.Contravariant.Day" "Day"+#else+dayTyCon = mkTyCon "Data.Functor.Contravariant.Day.Day"+#endif++#endif++instance Contravariant (Day f g) where+  contramap f (Day fb gc abc) = Day fb gc (abc . f)++-- | Break apart the Day convolution of two contravariant functors.+runDay :: (Contravariant f, Contravariant g) => Day f g a -> (f a, g a)+runDay (Day fb gc abc) =+  ( contramap (fst . abc) fb+  , contramap (snd . abc) gc+  )++-- | Day convolution provides a monoidal product. The associativity+-- of this monoid is witnessed by 'assoc' and 'disassoc'.+--+-- @+-- 'assoc' . 'disassoc' = 'id'+-- 'disassoc' . 'assoc' = 'id'+-- 'contramap' f '.' 'assoc' = 'assoc' '.' 'contramap' f+-- @+assoc :: Day f (Day g h) a -> Day (Day f g) h a+assoc (Day fb (Day gd he cde) abc) = Day (Day fb gd id) he $ \a ->+  case cde <$> abc a of+    (b, (d, e)) -> ((b, d), e)++-- | Day convolution provides a monoidal product. The associativity+-- of this monoid is witnessed by 'assoc' and 'disassoc'.+--+-- @+-- 'assoc' . 'disassoc' = 'id'+-- 'disassoc' . 'assoc' = 'id'+-- 'contramap' f '.' 'disassoc' = 'disassoc' '.' 'contramap' f+-- @+disassoc :: Day (Day f g) h a -> Day f (Day g h) a+disassoc (Day (Day fd ge bde) hc abc) = Day fd (Day ge hc id) $ \a ->+  case abc a of+    (b, c) -> case bde b of+      (d, e) -> (d, (e, c))++-- | The monoid for Day convolution /in Haskell/ is symmetric.+--+-- @+-- 'contramap' f '.' 'swapped' = 'swapped' '.' 'contramap' f+-- @+swapped :: Day f g a -> Day g f a+swapped (Day fb gc abc) = Day gc fb (swap . abc)++-- | Proxy serves as the unit of Day convolution.+--+-- @+-- 'day1' '.' 'intro1' = 'id'+-- 'contramap' f '.' 'intro1' = 'intro1' '.' 'contramap' f+-- @+intro1 :: f a -> Day Proxy f a+intro1 fa = Day Proxy fa $ \a -> ((),a)++-- | Proxy serves as the unit of Day convolution.+--+-- @+-- 'day2' '.' 'intro2' = 'id'+-- 'contramap' f '.' 'intro2' = 'intro2' '.' 'contramap' f+-- @+intro2 :: f a -> Day f Proxy a+intro2 fa = Day fa Proxy $ \a -> (a,())++-- | In Haskell we can do general purpose elimination, but in a more general setting+-- it is only possible to eliminate the unit.+--+-- @+-- 'day1' '.' 'intro1' = 'id'+-- 'day1' = 'fst' '.' 'runDay'+-- 'contramap' f '.' 'day1' = 'day1' '.' 'contramap' f+-- @+day1 :: Contravariant f => Day f g a -> f a+day1 (Day fb _ abc) = contramap (fst . abc) fb++-- | In Haskell we can do general purpose elimination, but in a more general setting+-- it is only possible to eliminate the unit.+-- @+-- 'day2' '.' 'intro2' = 'id'+-- 'day2' = 'snd' '.' 'runDay'+-- 'contramap' f '.' 'day2' = 'day2' '.' 'contramap' f+-- @+day2 :: Contravariant g => Day f g a -> g a+day2 (Day _ gc abc) = contramap (snd . abc) gc++-- | Diagonalize the Day convolution:+--+-- @+-- 'day1' '.' 'diag' = 'id'+-- 'day2' '.' 'diag' = 'id'+-- 'runDay '.' 'diag' = \a -> (a,a)+-- 'contramap' f . 'diag' = 'diag' . 'contramap' f+-- @++diag :: f a -> Day f f a+diag fa = Day fa fa $ \a -> (a,a)++-- | Apply a natural transformation to the left-hand side of a Day convolution.+--+-- This respects the naturality of the natural transformation you supplied:+--+-- @+-- 'contramap' f '.' 'trans1' fg = 'trans1' fg '.' 'contramap' f+-- @+trans1 :: (forall x. f x -> g x) -> Day f h a -> Day g h a+trans1 fg (Day fb hc abc) = Day (fg fb) hc abc++-- | Apply a natural transformation to the right-hand side of a Day convolution.+--+-- This respects the naturality of the natural transformation you supplied:+--+-- @+-- 'contramap' f '.' 'trans2' fg = 'trans2' fg '.' 'contramap' f+-- @+trans2 :: (forall x. g x -> h x) -> Day f g a -> Day f h a+trans2 gh (Day fb gc abc) = Day fb (gh gc) abc

@@ -1,6 +1,6 @@ name:          contravariant category:      Control, Data-version:       0.4+version:       0.4.1 license:       BSD3 cabal-version: >= 1.6 license-file:  LICENSE@@ -9,9 +9,9 @@ stability:     provisional homepage:      http://github.com/ekmett/contravariant/ bug-reports:   http://github.com/ekmett/contravariant/issues-copyright:     Copyright (C) 2007-2011 Edward A. Kmett-synopsis:      Haskell 98 contravariant functors-description:   Haskell 98 contravariant functors+copyright:     Copyright (C) 2007-2013 Edward A. Kmett+synopsis:      Contravariant functors+description:   Contravariant functors build-type:    Simple extra-source-files:   .travis.yml@@ -30,4 +30,5 @@   exposed-modules:     Data.Functor.Contravariant     Data.Functor.Contravariant.Compose+    Data.Functor.Contravariant.Day   ghc-options: -Wall