par-dual (empty) → 0.1.0.0
raw patch · 6 files changed
+760/−0 lines, 6 filesdep +asyncdep +basedep +hedgehogsetup-changed
Dependencies added: async, base, hedgehog, par-dual, refined, template-haskell, validators
Files
- LICENSE +201/−0
- README.md +209/−0
- Setup.hs +2/−0
- par-dual.cabal +38/−0
- src/Control/ParDual/Class.hs +178/−0
- test/Main.hs +132/−0
+ LICENSE view
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+ README.md view
@@ -0,0 +1,209 @@+# par-dual++[](https://github.com/gvolpe/par-dual/actions)++The [PureScript](https://www.purescript.org/) language defines a [Parallel](https://pursuit.purescript.org/packages/purescript-parallel/4.0.0/docs/Control.Parallel.Class#t:Parallel) typeclass in the `parallel` package. Quoting its documentation:++> The `Parallel` class abstracts over monads which support parallel composition via some related `Applicative`.++The same typeclass is defined in the [Scala](https://www.scala-lang.org/) language, as part of the [Cats](https://typelevel.org/cats/typeclasses/parallel.html) library.++This typeclass has been controversial, in a sense, for not having strong laws. However, it has been proven to be actually useful in real-world applications.++The idea of this package is to bring this power over to the Haskell language while exploring the design space to identify and define stronger laws (if possible).++Originally, this idea has been described in [this blogpost](https://gvolpe.github.io/blog/parallel-typeclass-for-haskell/).++## ParDual++Here's the definition of the same typeclass in Haskell:++```haskell+class (Monad m, Applicative f) => ParDual f m | m -> f, f -> m where+ parallel :: forall a . m a -> f a+ sequential :: forall a . f a -> m a+```++I decided to call it `ParDual` instead of `Parallel`, because this *duality* doesn't always define a `sequential` and `parallel` relationship. Such is the case between `[]` and `ZipList`, as we will soon discover.++It defines two functions, which are natural transformations between a `Monad m` and an `Applicative f`. It could also be seen as a typeclass version of an isomorphism such as `forall a . Iso (f a) (m a)`.++The most common and useful relationships are both `Either` / `Validation` and `IO` / `Concurrently`.++```haskell+instance Semigroup e => ParDual (Validation e) (Either e) where+ parallel = fromEither+ sequential = toEither++instance ParDual Concurrently IO where+ parallel = Concurrently+ sequential = runConcurrently+```++`Validation` comes from the [validators](https://hackage.haskell.org/package/validators) package, whereas `Concurrently` comes from the [async](https://hackage.haskell.org/package/async) package.++Additionally, we can define a lot of powerful functions solely in terms of `Applicative`, `Monad`, and `ParDual`. A few other functions might require extra requirements, such as `Traversable`.++### parMapN++The `parMapN` set of functions are analogue to combining `<$>` and `<*>`, for any dual `Applicative`.++```haskell+parMap2+ :: (Applicative f, Monad m, ParDual f m)+ => m a0+ -> m a1+ -> (a0 -> a1 -> a)+ -> m a+```++In this case, `parMap2` takes only two computations and a function, but you can find other versions up to `parMap6`. If there is demand, we can consider abstracting over its arity, in order to compose an arbitrary number of computations.++For example, if we define a `Person` datatype with two fields:++```haskell+type Name = Refined NonEmpty String+type Age = Refined (GreaterThan 17) Int++data Person = Person+ { personAge :: Age+ , personName :: Name+ } deriving Show+```++We can then validate different inputs, while accumulating errors on the left side, even when our type is `Either [String] Person`.++```haskell+mkPerson :: Int -> String -> Either [String] Person+mkPerson a n = parMap2 (ref a) (ref n) Person+```++Where `ref` is a generic function that converts `RefineException`s to `[String]`:++```haskell+ref :: Predicate p x => x -> Either [String] (Refined p x)+ref x = left (\e -> [show e]) (refine x)+```++In case of two invalid inputs, we will get as a result a list of validation errors:++```haskell+mkPerson 10 "" == Left ["error 1", "error 2"]+```++If `parMapN` didn't exist, we could do the same by manually converting between `Either` and `Validation` (which is exactly what `parMapN` does via the `ParDual` class).++```haskell+mkPerson :: Int -> String -> Either [String] Person+mkPerson a n = toEither $ Person <$> fromEither (ref a) <*> fromEither (ref n)+```++Though, we can see how cumbersome and boilerplatey it gets.++### parTraverse++Another great application of the `ParDual` class is the definition of a `traverse` function that takes a `Monad` and a `Traversable t`, but that operates over its dual `Applicative`, and at the end it converts back to this `Monad`.++```haskell+parTraverse+ :: (Traversable t, Applicative f, Monad m, ParDual f m)+ => (a -> m b)+ -> t a+ -> m (t b)+```++The type signature is exactly the same as `traverse`, except the constraints are different.++We can appreciate its usability by looking at some examples. Here's one with `Either`:++```haskell+f :: Int -> Either [String] Int+f n = Left [show n]++traverse f [1..5] == Left ["1"]+parTraverse f [1..5] == Left ["1","2","3","4","5"]+```++Below there is another one with `IO`:++```haskell+randomDelay :: IO ()+randomDelay = do+ r <- randomRIO (1, 10)+ threadDelay (r * 500000)++traverseIO :: IO ()+traverseIO = traverse_ (\n -> randomDelay >> print n) [1 .. 10]++parTraverseIO :: IO ()+parTraverseIO = parTraverse_ (\n -> randomDelay >> print n) [1 .. 10]+```++The `traverse` version prints out numbers from 1 to 10 in sequence, while waiting for every random delay. So the output is pretty much `1 2 3 4 5 6 7 8 9 10`.++The `parTraverse` version has a non-deterministic output, since it goes through `Concurrently` (`IO`'s dual). It is exactly what you would expect while using [mapConcurrently](https://hackage.haskell.org/package/async-2.2.2/docs/Control-Concurrent-Async.html#v:mapConcurrently). One possible output is `5 10 6 1 3 2 9 4 7 8`.++### ZipList++The dual `Applicative` instance of `[]` is the one defined by `ZipList`, which doesn't have anything to do with parallelism.++```haskell+instance ParDual ZipList [] where+ parallel = ZipList+ sequential = getZipList+```++Let's have a look at the examples shown below.++```haskell+((+) <$> [1..5] <*> [6..10]) == [7,8,9,10,11,8,9,10,11,12,9,10,11,12,13,10,11,12,13,14,11,12,13,14,15]++parMap2 [1..5] [6..10] (+) == [7,9,11,13,15]+```++The standard version iterates over both lists "sequentially". That is, it iterates over the first one, and then over the second one, returning the cartesian product of both lists.++Conversely, `ZipList`s only return the sum of the current elements of both lists such as `1 + 6`, `2 + 7`, and so on. It iterates over both lists in "parallel", effectively traversing both at once.++### parBitraverse++Operates over any `Bitraversable` such as `Either` or `(,,)`.++```haskell+res1 = [("ba",'2','T'),("ba",'2','r'),("ba",'2','u'),("ba",'2','e'),("ba",'4','T'),("ba",'4','r'),("ba",'4','u'),("ba",'4','e')]++(bitraverse show show ("ba", 24, True)) == res1+```++The standard `bitraverse` for `(String, Int, Bool)` traverses over the second value and then over the third value, combining the results on each iteration.++```haskell+(parBitraverse show show ("ba", 24, True)) == [("ba",'2','T'),("ba",'4','r')]+```++The dual variant traverses all the values at the same time, terminating as soon as either value is empty.++## Test suite++The test suite property-checks the functions defined in `ParDual` applied to different types of values.++```+$ nix-shell --run 'cabal new-run par-dual-tests'+━━━ Main ━━━+ ✓ prop_parMap2_on_success passed 100 tests.+ ✓ prop_parMap2_accumulates_errors passed 100 tests.+ ✓ prop_parTraverse_accumulates_errors passed 100 tests.+ ✓ prop_parTraverse_io_is_concurrent passed 10 tests.+ ✓ prop_parMap2_on_lists passed 100 tests.+ ✓ prop_parBitraverse passed 100 tests.+ ✓ 6 succeeded.+```++## Publishing++Generating documentation and tarball file to upload.++```+$ cabal new-haddock --haddock-for-hackage --enable-doc+$ cabal upload -d dist-newstyle/par-dual-0.1.0.0-docs.tar.gz+$ cabal new-sdist
+ Setup.hs view
@@ -0,0 +1,2 @@+import Distribution.Simple+main = defaultMain
+ par-dual.cabal view
@@ -0,0 +1,38 @@+cabal-version: 2.4++name: par-dual+version: 0.1.0.0+synopsis: ParDual class for Parallel <-> Sequential+description: Defines a ParDual class for a Parallel <-> Sequential relationship+homepage: https://github.com/gvolpe/par-dual+bug-reports: https://github.com/gvolpe/par-dual/issues+license: Apache-2.0+license-file: LICENSE+category: Library+author: Gabriel Volpe+copyright: 2020 - Gabriel Volpe+maintainer: volpegabriel@gmail.com+build-type: Simple+extra-source-files: README.md++library+ exposed-modules: Control.ParDual.Class+ build-depends: base >= 4.13.0 && < 4.14+ , async >= 2.2.2 && < 2.3+ , validators >= 0.0.1 && < 0.1+ hs-source-dirs: src+ default-language: Haskell2010+ ghc-options: -Wall++test-Suite par-dual-tests+ type: exitcode-stdio-1.0+ main-is: Main.hs+ hs-source-dirs: test+ build-depends: base+ , hedgehog+ , par-dual+ , refined+ , template-haskell+ , validators+ default-language: Haskell2010+ ghc-options: -Wall -threaded -with-rtsopts -N
+ src/Control/ParDual/Class.hs view
@@ -0,0 +1,178 @@+{-# LANGUAGE FunctionalDependencies, RankNTypes, TypeOperators #-}++{-|+Module : Control.ParDual.Class+Description : Definition of the 'ParDual' class and its functions.+Copyright : (c) Gabriel Volpe, 2020+License : Apache-2.0+Maintainer : volpegabriel@gmail.com+Stability : experimental++You can find here functions such as 'parMap2', 'parTraverse', 'parBitraverse', etc.+-}+module Control.ParDual.Class where++import Control.Applicative ( ZipList(..) )+import Control.Concurrent.Async ( Concurrently(..) )+import Data.Bitraversable ( Bitraversable+ , bitraverse+ )+import Data.Functor ( void )+import Data.Validation ( Validation+ , toEither+ , fromEither+ )++{- | The ParDual class abstracts over 'Monad's that have a dual+'Applicative' instance that acts in a different useful way.++E.g., the duality between 'Either' and 'Validation'. As well+as the duality between 'IO' and 'Concurrently'.++It can also be seen as an isomorphism defined at the class level.+-}+class (Monad m, Applicative f) => ParDual f m | m -> f, f -> m where+ {- | A natural transformation from 'm' to 'f'+ -}+ parallel :: forall a . m a -> f a++ {- | A natural transformation from 'f' to 'm'+ -}+ sequential :: forall a . f a -> m a++ {- |+ It is the analogue to using '<$>' and '<*>' for the dual+ 'Applicative' of the current 'Monad', as defined by the+ relationship defined by the 'ParDual' instance.+ -}+ parMap2 :: m a0 -> m a1 -> (a0 -> a1 -> a) -> m a+ parMap2 ma0 ma1 f = sequential $ f+ <$> parallel ma0+ <*> parallel ma1++ {- |+ It is the analogue to using '<$>' and '<*>' for the dual+ 'Applicative' of the current 'Monad', as defined by the+ relationship defined by the 'ParDual' instance.+ -}+ parMap3 :: m a0 -> m a1 -> m a2 -> (a0 -> a1 -> a2 -> a) -> m a+ parMap3 ma0 ma1 ma2 f = sequential $ f+ <$> parallel ma0+ <*> parallel ma1+ <*> parallel ma2++ {- |+ It is the analogue to using '<$>' and '<*>' for the dual+ 'Applicative' of the current 'Monad', as defined by the+ relationship defined by the 'ParDual' instance.+ -}+ parMap4 :: m a0 -> m a1 -> m a2 -> m a3 -> (a0 -> a1 -> a2 -> a3 -> a) -> m a+ parMap4 ma0 ma1 ma2 ma3 f = sequential $ f+ <$> parallel ma0+ <*> parallel ma1+ <*> parallel ma2+ <*> parallel ma3++ {- |+ It is the analogue to using '<$>' and '<*>' for the dual+ 'Applicative' of the current 'Monad', as defined by the+ relationship defined by the 'ParDual' instance.+ -}+ parMap5 :: m a0 -> m a1 -> m a2 -> m a3 -> m a4 -> (a0 -> a1 -> a2 -> a3 -> a4 -> a) -> m a+ parMap5 ma0 ma1 ma2 ma3 ma4 f = sequential $ f+ <$> parallel ma0+ <*> parallel ma1+ <*> parallel ma2+ <*> parallel ma3+ <*> parallel ma4++ {- |+ It is the analogue to using '<$>' and '<*>' for the dual+ 'Applicative' of the current 'Monad', as defined by the+ relationship defined by the 'ParDual' instance.+ -}+ parMap6 :: m a0 -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> (a0 -> a1 -> a2 -> a3 -> a4 -> a5 -> a) -> m a+ parMap6 ma0 ma1 ma2 ma3 ma4 ma5 f = sequential $ f+ <$> parallel ma0+ <*> parallel ma1+ <*> parallel ma2+ <*> parallel ma3+ <*> parallel ma4+ <*> parallel ma5++ {- |+ Same as 'traverse', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parTraverse :: Traversable t => (a -> m b) -> t a -> m (t b)+ parTraverse f ta =+ let g a = parallel (f a)+ res = sequenceA $ fmap g ta+ in sequential res++ {- |+ Same as 'Data.Foldable.traverse_', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parTraverse_ :: Traversable t => (a -> m b) -> t a -> m ()+ parTraverse_ f = void . parTraverse f++ {- |+ Same as 'sequence', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parSequence :: Traversable t => t (m a) -> m (t a)+ parSequence = parTraverse id++ {- |+ Same as 'sequence_', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parSequence_ :: Traversable t => t (m a) -> m ()+ parSequence_ = void . parSequence++ {- |+ Same as '*>', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parProductR :: m a -> m b -> m b+ parProductR ma mb = parMap2 ma mb (\_ b -> b)++ {- |+ Same as '<*', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parProductL :: m a -> m b -> m a+ parProductL ma mb = parMap2 ma mb const++ {- |+ Same as 'bitraverse', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parBitraverse :: Bitraversable t => (a -> m c) -> (b -> m d) -> t a b -> m (t c d)+ parBitraverse ma mb tab =+ let fa = (\a -> parallel (ma a))+ fb = (\b -> parallel (mb b))+ res = bitraverse fa fb tab+ in sequential res++ {- |+ Same as 'Data.Traversable.bisequence', except it uses the dual 'Applicative' of+ the current 'Monad', as defined by the 'ParDual' relationship.+ -}+ parBisequence :: Bitraversable t => t (m a) (m b) -> m (t a b)+ parBisequence = parBitraverse id id++--------------------- Instances ----------------------------++instance Semigroup e => ParDual (Validation e) (Either e) where+ parallel = fromEither+ sequential = toEither++instance ParDual Concurrently IO where+ parallel = Concurrently+ sequential = runConcurrently++instance ParDual ZipList [] where+ parallel = ZipList+ sequential = getZipList
+ test/Main.hs view
@@ -0,0 +1,132 @@+{-# LANGUAGE DataKinds, OverloadedStrings, TemplateHaskell #-}++module Main where++import Control.Arrow ( left )+import Control.Concurrent ( threadDelay )+import Control.ParDual.Class+import Control.Monad ( unless )+import Data.Bitraversable ( bitraverse )+import Data.Foldable ( traverse_ )+import Data.IORef+import Data.Validation ( fromEither+ , toEither+ )+import Hedgehog+import qualified Hedgehog.Gen as Gen+import qualified Hedgehog.Range as Range+import Refined+import System.Exit ( exitFailure )++main :: IO ()+main = do+ results <- sequence [checkParallel dualTests]+ unless (and results) exitFailure++dualTests :: Group+dualTests = $$(discover)++prop_parMap2_on_success :: Property+prop_parMap2_on_success = property $ do+ a <- forAll $ Gen.int (Range.linear 18 100)+ n <- forAll $ Gen.list (Range.linear 1 50) Gen.alpha+ let result = parMap2 (ref a) (ref n) Person+ expected = Person <$> ref a <*> ref n+ result === expected++prop_parMap2_accumulates_errors :: Property+prop_parMap2_accumulates_errors = property $ do+ a <- forAll $ Gen.int (Range.linear 0 17)+ n <- forAll $ Gen.list (Range.linear 0 0) Gen.alpha+ let+ res1 = parMap2 (ref a) (ref n) Person+ res2 = Person <$> ref a <*> ref n+ exp1 = Left+ [ "The predicate (GreaterThan 17) does not hold: \n Value is not greater than 17"+ , "The predicate (SizeGreaterThan 0) does not hold: \n Size of Foldable is not greater than 0\n Size is: 0"+ ]+ exp2 = left (take 1) exp1+ res1 === exp1+ res2 === exp2++prop_parTraverse_accumulates_errors :: Property+prop_parTraverse_accumulates_errors = property $ do+ xs <- forAll $ Gen.list (Range.linear 1 10) (Gen.int (Range.linear 1 10))+ let f :: Int -> Either [String] Int+ f n = Left [show n]+ res1 = parTraverse f xs+ res2 = traverse f xs+ exp1 = Left (show <$> xs)+ exp2 = Left (take 1 $ show <$> xs)+ res1 === exp1+ res2 === exp2++-- This one is tricky to test but this seems good enough for now+prop_parTraverse_io_is_concurrent :: Property+prop_parTraverse_io_is_concurrent = withTests (10 :: TestLimit) $ property $ do+ xs <- forAll $ Gen.list (Range.linear 15 25) (Gen.int (Range.linear 1 10))+ let f r n = threadDelay (1 * 3000) >> atomicModifyIORef r (\x -> (n : x, n))+ ref1 <- evalIO $ newIORef [] :: PropertyT IO (IORef [Int])+ ref2 <- evalIO $ newIORef [] :: PropertyT IO (IORef [Int])+ evalIO $ parTraverse_ (f ref1) xs+ evalIO $ traverse_ (f ref2) xs+ res1 <- evalIO $ readIORef ref1+ res2 <- evalIO $ readIORef ref2+ -- Avoid cases where all elements are the same (could prob. be done in a better way)+ let exp1 = if and (fmap (== head xs) (tail xs)) then [] else reverse xs+ res1 /== exp1+ res2 === reverse xs++prop_parMap2_on_lists :: Property+prop_parMap2_on_lists = property $ do+ xs <- forAll $ Gen.constant [1 .. 5] :: PropertyT IO [Int]+ ys <- forAll $ Gen.constant [6 .. 10] :: PropertyT IO [Int]+ let res1 = parMap2 xs ys (+)+ res2 = (+) <$> xs <*> ys+ exp1 = [7, 9, 11, 13, 15]+ exp2 = [7 .. 11] ++ [8 .. 12] ++ [9 .. 13] ++ [10 .. 14] ++ [11 .. 15]+ res1 === exp1+ res2 === exp2++prop_parBitraverse :: Property+prop_parBitraverse = property $ do+ a <- forAll $ Gen.list (Range.linear 5 10) Gen.alpha+ b <- forAll $ Gen.int (Range.linear 5 10)+ c <- forAll Gen.bool+ let res1 = parBitraverse show show (a, b, c)+ res2 = bitraverse show show (a, b, c)+ length res1 === min (length $ show b) (length $ show c)+ length res2 === length (show b) * length (show c)++-------------- Datatypes -------------------------++type Name = Refined NonEmpty String+type Age = Refined (GreaterThan 17) Int++data Person = Person+ { personAge :: Age+ , personName :: Name+ } deriving (Eq, Show)++-------------- Sequential Validation -------------++mkPersonSeq :: Int -> String -> Either RefineException Person+mkPersonSeq a n = do+ age <- refine a+ name <- refine n+ return $ Person age name++-------------- Parallel Validation (manually) -------------------++type Eff a = Either [String] a++ref :: Predicate p x => x -> Eff (Refined p x)+ref x = left (\e -> [show e]) (refine x)++mkPerson :: Int -> String -> Eff Person+mkPerson a n = toEither $ Person <$> fromEither (ref a) <*> fromEither (ref n)++-------------- Parallel Validation -------------++makePerson :: Int -> String -> Eff Person+makePerson a n = parMap2 (ref a) (ref n) Person