pipes (empty) → 1.0
raw patch · 5 files changed
+1524/−0 lines, 5 filesdep +basedep +mtlsetup-changed
Dependencies added: base, mtl
Files
- Control/Pipe.hs +501/−0
- Control/Pipe/Common.hs +281/−0
- LICENSE +674/−0
- Setup.hs +2/−0
- pipes.cabal +66/−0
+ Control/Pipe.hs view
@@ -0,0 +1,501 @@+{-+ Copyright 2012 Gabriel Gonzalez++ This file is part of the Haskell Pipes Library.++ The is free software: you can redistribute it and/or modify+ it under the terms of the GNU General Public License as published by+ the Free Software Foundation, either version 3 of the License, or+ (at your option) any later version.++ hPDB is distributed in the hope that it will be useful,+ but WITHOUT ANY WARRANTY; without even the implied warranty of+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the+ GNU General Public License for more details.++ You should have received a copy of the GNU General Public License+ along with the Haskell Pipes Library. If not, see+ <http://www.gnu.org/licenses/>.+-}++{-|+ This library only provides a single data type: 'Pipe'.++ 'Pipe' is a monad transformer that extends the base monad with the ability+ to 'await' input from or 'yield' output to other 'Pipe's. 'Pipe's resemble+ enumeratees in other libraries because they receive an input stream and+ transform it into a new stream.++ I'll introduce our first 'Pipe', which is a verbose version of the Prelude's+ 'take' function:++> take' :: Int -> Pipe a a IO ()+> take' n = do+> replicateM_ n $ do+> x <- await+> yield x+> lift $ putStrLn "You shall not pass!"++ This 'Pipe' allows the first @n@ values it receives to pass through+ undisturbed, then it outputs a cute message and shuts down. Shutdown is+ automatic when you reach the end of the monad. You don't need to send a+ special signal to connected 'Pipe's to let them know you are done handling+ input or generating output.++ Let's dissect the above 'Pipe''s type to learn a bit about how 'Pipe's work:++> | Input Type | Output Type | Base monad | Return value+> Pipe a a IO ()++ So @take'@ 'await's input of type @a@ from upstream 'Pipe's and 'yield's+ output of type @a@ to downstream 'Pipe's. @take'@ uses 'IO' as its base+ monad because it invokes the 'putStrLn' function. If we remove the call to+ 'putStrLn' the compiler infers the following type instead, which is+ polymorphic in the base monad:++> take' :: (Monad m) => Int -> Pipe a a m ()++ 'Pipe's are conservative about using the base monad. In fact, you can only+ invoke the base monad by using the 'lift' function from 'Pipe''s+ 'MonadTrans' instance. If you never use 'lift', your 'Pipe' will translate+ into pure code.++ Now let's create a function that converts a list into a 'Pipe' by+ 'yield'ing each element of the list:++> fromList :: (Monad m) => [a] -> Pipe Zero a m ()+> fromList = mapM_ yield++ The 'Zero' in the type signature represents a type with no constructors+ and we use it to block the input end of the 'Pipe' so that it can't request+ any input from an upstream 'Pipe'. You can think of @fromList@ as a one way+ 'Pipe' that can only deliver output, which makes it suitable for the first+ stage in a 'Pipeline'. I provide a type synonym for this common case:++> type Producer b m r = Pipe Zero b m r++ You can then rewrite the type signature for @fromList@ as:++> fromList :: (Monad m) => [a] -> Producer a m ()++ Note that you don't have to block the input end with the 'Zero' type. If+ you let the compiler infer the type, you would get:++> fromList :: (Monad m) => [a] -> Pipe b a m ()++ The compiler says that the input could be anything since without any calls+ to 'await' it can't infer the input type. I only provide the 'Zero' type+ as a convenience so that you can intentionally block 'Pipe' ends.++ 'Producer's resemble enumerators in other libraries because they are a data+ source. 'Producer's never use 'await' statements.++ Now let's create a 'Pipe' that prints every value delivered to it and never+ terminates:++> printer :: (Show a) => Pipe a Zero IO b+> printer = forever $ do+> x <- await+> lift $ print x++ The 'Zero' in @printer@'s type signature indicates that it never delivers+ output downstream, so it represents the final stage in a 'Pipeline'. Again,+ I provide a type synonym for this common case:++> type Consumer a m r = Pipe a Zero m r++ So we could instead write @printer@'s type as:++> printer :: (Show a) => Consumer a IO b++ 'Consumer's resemble iteratees in other libraries because they are a data+ sink. 'Consumer's never use 'yield' statements.++ What distinguishes 'Pipe's from every other iteratee implementation is that+ they form a 'Category'. Because of this, you can literally compose 'Pipe's+ into 'Pipeline's. 'Pipe's actually possess two 'Category' instances:++> newtype Lazy m r a b = Lazy { unLazy :: Pipe a b m r }+> newtype Strict m r a b = Strict { unStrict :: Pipe a b m r }+> instance Category (Lazy m r) where ...+> instance Category (Strict m r) where ...++ The first category composes pipes with 'Lazy' semantics and the second one+ composes 'Pipe's with 'Strict' semantics. I'll begin by demonstrating+ 'Lazy' semantics.++ For example, you can compose the above 'Pipe's with:++> pipeline :: Pipe Zero Zero IO ()+> pipeline :: unLazy $ Lazy printer . Lazy (take 3) . Lazy (fromList [1..])++ The compiler deduces that the final 'Pipe' must be blocked at both ends,+ meaning it will never 'await' any input and it will never 'yield' any+ output. This represents a self-contained 'Pipeline' and I provide a type+ synonym for this common case:++> type Pipeline m r = Pipe Zero Zero m r++ Also, I provide convenience operators for composing 'Pipe's without the+ burden of wrapping and unwrapping newtypes. For example, to compose 'Pipe's+ using 'Lazy' semantics, just use the '<+<' operator:++> p1 <+< p2 = unLazy $ Lazy p1 <<< Lazy p2 -- (<<<) is the same as (.)++ So you can rewrite @pipeline@ as:++> pipeline :: Pipeline IO ()+> pipeline = printer <+< take 3 <+< fromList [1..]++ Like many other monad transformers, you convert the 'Pipe' monad back to the+ base monad using some sort of \"@run...@\" function. In this case, it's the+ 'runPipe' function:++> runPipe :: (Monad m) => Pipeline m r -> m r++ 'runPipe' only works on self-contained 'Pipeline's. This is the only+ function in the entire library that actually requires the 'Zero' type+ because it must guarantee that its argument 'Pipe' will never try to+ 'await' or 'yield'. You don't need to worry about explicitly giving it+ capped 'Pipe's because self-contained 'Pipe's will automatically have+ polymorphic input and output ends and 'runPipe' will just assume those ends+ are 'Zero'.++ Let's try using 'runPipe':++>>> runPipe pipeline+1+2+3+You shall not pass!++ Fascinating! Our 'Pipe' terminated even though @printer@ never terminates+ and @fromList@ never terminates when given an infinite list. To illustrate+ why our 'Pipe' terminated, let's outline the 'Pipe' flow control rules for+ 'Lazy' composition:++ * Execution begins at the most downstream 'Pipe' (@printer@ in our example).++ * If a 'Pipe' 'await's input, it blocks and transfers control to the next+ 'Pipe' upstream until that 'Pipe' 'yield's back a value.++ * If a 'Pipe' 'yield's output, it restores control to the original+ downstream 'Pipe' that was 'await'ing its input and binds its result to+ the return value of the 'await' command.++ * If a 'Pipe' terminates, it terminates every other 'Pipe' composed with it.++ The last rule follows from laziness. If a 'Pipe' terminates then every+ downstream 'Pipe' depending on its output cannot proceed, and upstream+ 'Pipe's are never evaluated because the terminated 'Pipe' will not request+ values from them any longer.++ So in our previous example, the 'Pipeline' terminated because @take' 3@+ terminated and brought down the entire 'Pipeline' with it.++ 'Pipe's promote loose coupling, allowing you to mix and match them+ transparently using composition. For example, we can define a new+ 'Producer' pipe that indefinitely prompts the user for integers:++> prompt :: Producer Int IO a+> prompt = forever $ do+> lift $ putStrLn "Enter a number: "+> n <- read <$> lift getLine+> yield n++ Now we can compose it with any of our previous 'Pipe's:++>>> runPipe $ printer <+< take' 3 <+< prompt+Enter a number:+1<Enter>+1+Enter a number:+2<Enter>+2+Enter a number:+3<Enter>+3+You shall not pass!++ You can easily \"vertically\" concatenate 'Pipe's, 'Producer's, and+ 'Consumer's, all using simple monad sequencing: ('>>'). For example, here+ is how you concatenate 'Producer's:++>>> runPipe $ printer <+< (fromList [1..3] >> fromList [10..12])+1+2+3+10+11+12++ Here's how you would concatenate 'Consumer's:++>>> let print' n = printer <+< take' n :: (Show a) => Int -> Consumer a IO ()+>>> runPipe $ (print' 3 >> print' 4) <+< fromList [1..]+1+2+3+You shall not pass!+4+5+6+7+You shall not pass!++ ... but the above example is gratuitous because we could have just+ concatenated the intermediate @take'@ 'Pipe':++>>> runPipe $ printer <+< (take' 3 >> take' 4) <+< fromList [1..]+1+2+3+You shall not pass!+4+5+6+7+You shall not pass!++ Pipe composition imposes an important limitation: You can only compose+ 'Pipe's that have the same return type. For example, I could write the+ following function:++> deliver :: (Monad m) => Int -> Consumer a m [a]+> deliver n = replicateM n await++ ... and I might try to compose it with @fromList@:++>>> runPipe $ deliver 3 <+< fromList [1..10] -- wrong!++ ... but this wouldn't type-check, because @fromList@ has a return type of+ @()@ and @deliver@ has a return type of @[Int]@. 'Lazy' composition+ requires that every 'Pipe' has a return value ready in case it terminates+ first. This was not a conscious design choice, but rather a requirement of+ the 'Category' instance.++ Fortunately, we don't have to rewrite the @fromList@ function because we can+ add a return value using vertical concatenation:++>>> runPipe $ deliver 3 <+< (fromList [1..10] >> return [])+[1,2,3]++ ... although a more idiomatic Haskell version would be:++>>> runPipe $ (Just <$> deliver 3) <+< (fromList [1..10] *> pure Nothing)+Just [1,2,3]++ This forces you to cover all code paths by thinking about what return value+ you would provide if something were to go wrong. For example, let's say I+ make a mistake and request more input than @fromList@ can deliver:++>>> runPipe $ (Just <$> deliver 99) <+< (fromList [1..10] *> pure Nothing)+Nothing++ The type system saved me by forcing me to handle all possible ways my+ program could terminate.++ Now what if you want to write a 'Pipe' that only reads from its input end+ (i.e. a 'Consumer') and returns a list of every value delivered to it when+ its input 'Pipe' terminates?++> toList :: (Monad m) => Consumer a m [a]+> toList = ???++ You can't write such a 'Pipe' because if its input terminates then it brings+ down @toList@ with it! This is a good thing because @toList@ as defined+ is not compositional.++ To see why, let's say you somehow got @toList@ to work and the following+ imaginary code sample worked:++>>> runPipe $ toList <+< (fromList [1..5] >> return [])+[1,2,3,4,5]++ @toList@ is defined to return its value when the 'Pipe' immediately upstream+ (@fromList@ in this case) terminates. This behavior immediately leads to a+ problem. What if I were to insert an \"identity\" 'Pipe' between+ @toList@ and @fromList@:++> identity = forever $ await >>= yield+> -- This is how id in both categories is actually implemented++ This 'Pipe' forwards every valued untouched, so we would expect it to not+ have any affect if we were to insert it in the middle:++>>> runPipe $ toList <+< identity <+< (fromList [1..5] >> return [])+??? -- Oops! Something other than [1,2,3,4,5], perhaps even non-termination++ The answer couldn't be @[1,2,3,4,5]@ because @toList@ would monitor + @identity@ instead of @fromList@ and since @identity@ never terminates+ @toList@ never terminates. This is what I mean when I say that @toList@'s+ specified behavior is non-compositional. It only works if it is coupled+ directly to the desired 'Pipe' and breaks when you introduce intermediate+ stages.++ This fortunate limitation was not an intentional design choice, but rather+ an inadvertent consequence of enforcing the 'Category' laws when I was+ implementing 'Pipe''s 'Category' instance. Satisfying the 'Category' laws+ forces code to be compositional.++ Note that a terminated 'Pipe' only brings down 'Pipe's composed with it. To+ illustrate this, let's use the following example:++> p = do a <+< b+> c++ @a@, @b@, and @c@ are 'Pipe's, and @c@ shares the same input and output as+ @a <+< b@, otherwise we cannot combine them within the same monad. In the+ above example, either @a@ or @b@ could terminate and bring down the other+ one since they are composed, but @c@ is guaranteed to continue after+ @a <+< b@ terminates because it is not composed with them. Conceptually,+ we can think of this as @c@ automatically taking over the 'Pipe''s+ channeling responsibilities when @a <+< b@ can no longer continue. There+ is no need to \"restart\" the input or output manually as in some other+ iteratee libraries.++ The @pipes@ library, unlike other iteratee libraries, grounds its vertical+ and horizontal concatenation in mathematics by deriving horizontal+ concatenation ('.') from 'Category' instance and vertical concatenation+ ('>>') from its 'Monad' instance. This makes it easier to reason about+ 'Pipe's because you can leverage your intuition about 'Category's and+ 'Monad's to understand their behavior. The only 'Pipe'-specific primitives+ are the 'await' and 'yield' functions.++ 'Lazy' composition has one important defect: resource finalization. Let's+ say we have the file \"test.txt\" with the following contents:++> This is a test.+> Don't panic!+> Calm down, please!++ .. and we wish to lazily read a line at a time from it:++> readFile' :: Handle -> Producer Text IO ()+> readFile' h = do+> eof <- lift $ hIsEOF h+> if eof+> then return ()+> else do+> s <- lift $ hGetLine h+> yield s+> readFile' h++ We can use our 'Monad' and 'Category' instances to generate a+ resource-efficient version that only reads as many lines as we request:++> read' n = do+> lift $ putStrLn "Opening file ..."+> h <- lift $ openFile "test.txt"+> take' n <+< readFile' h+> lift $ putStrLn "Closing file ..."+> lift $ hClose h++ Now compose!++>>> runPipe $ printer <+< read' 2+Opening file ...+"This is a test."+"Don't panic!"+Closing file ...++>>> runPipe $ printer <+< read' 99+Opening file ...+"This is a test."+"Don't panic!"+"Calm down, please!"+Closing file ...++ In the first example, @take' n <+< readFile' h@ terminates because+ @take'@ only requested 2 lines. In the second example, it terminates+ because @readFile'@ ran out of input. However, in both cases the 'Pipe'+ never reads more lines than we request frees \"test.txt\" immediately when+ it was no longer needed.++ Even more importantly, the @file@ is never opened if we replace @printer@+ with a 'Pipe' that never demands input:++>>> runPipe $ (lift $ putStrLn "I don't need input") <+< read' 2+I don't need input++ There is still one problem, though. What if we wrote:++>>> runPipe $ printer <+< take' 1 <+< read' 3+Opening file ...+"This is a test."++ Oh no! Our 'Pipe' didn't properly close our file! @take' 1@ terminated+ before @read' 3@, preventing @read' 3@ from properly closing \"test.txt\".+ We can force the @read' 3@ 'Pipe' to close the file by using the 'discard'+ function:++> discard :: (Monad m) => Pipe a b m r+> discard = forever await++ If we append 'discard' to @take' 1@, we will drive @read' 3@ to completion+ by continuing to pull values from it:++>>> runPipe $ printer <+< (take' 1 >> discard) <+< read' 3+Opening file ...+"This is a test."+Closing file ...++ This allows @read' 3@ to complete so it can properly finalize itself. I+ include a convenience operator for this behavior:++> p1 <-< p2 = (p1 >> discard) <+< p2++ Interestingly, '<-<' forms a 'Category', too, namely the 'Strict' category.+ This 'Category' draws down all input by default (as the name suggests). I+ call it the 'Strict' 'Category' because 'discard' resembles 'seq'. 'discard'+ drives its input to continue until one upstream 'Pipe' terminates and this+ behavior resembles forcing its input to weak head normal form. If every+ 'Pipe' drives its input to weak head normal form, you get 'Strict'+ composition.++ 'Strict' composition works terribly on infinite inputs, as you would expect:++>>> runPipe $ printer <-< take' 3 <-< prompt+Enter a number:+1<Enter>+1+Enter a number:+2<Enter>+2+Enter a number:+3<Enter>+3+You shall not pass!+Enter a number:+4<Enter>+5<Enter>+6<Enter>+... <Prompts for input indefinitely and discards it>++ 'Strict' composition works best for inputs that are finite and require+ finalization. 'Lazy' composition works best for inputs that are infinite+ (and obviously an infinite input never needs finalization).++ However, unlike conventional strictness in Haskell, 'Strict' 'Pipe's do not+ load the entire input in memory. They still stream and immediately handle+ input just as 'Lazy' 'Pipe's. The only difference is that they guarantee+ input finalization (for better or for worse). Also, for 'Strict'+ 'Pipeline's the return value must come from the most upstream 'Pipe'. Other+ than that, 'Strict' composition will have the exact same sequence of monadic+ effects, resource usage, memory profile, and performance.++ Like Haskell, you can mix 'Lazy' and 'Strict' composition. Keep in mind,+ though, that while '<+<' is associative with itself and '<-<' is associative+ with itself, mixtures of them are not associative. Alternatively, you+ could stick to 'Lazy' composition and sprinkle 'discard' statements+ wherever you desire strictness. It's up to you. However, when designing+ library functions, make them 'Lazy' by default, since you can make 'Lazy'+ code 'Strict' by adding a 'discard' statement, but you can't make 'Strict'+ code 'Lazy'.+-}++module Control.Pipe (module Control.Pipe.Common) where++import Control.Category+import Control.Monad.Trans+import Control.Pipe.Common
+ Control/Pipe/Common.hs view
@@ -0,0 +1,281 @@+{-+ Copyright 2012 Gabriel Gonzalez++ This file is part of the Haskell Pipes Library.++ The is free software: you can redistribute it and/or modify+ it under the terms of the GNU General Public License as published by+ the Free Software Foundation, either version 3 of the License, or+ (at your option) any later version.++ hPDB is distributed in the hope that it will be useful,+ but WITHOUT ANY WARRANTY; without even the implied warranty of+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the+ GNU General Public License for more details.++ You should have received a copy of the GNU General Public License+ along with the Haskell Pipes Library. If not, see+ <http://www.gnu.org/licenses/>.+-}+{-# LANGUAGE Rank2Types #-}++module Control.Pipe.Common (+ -- * Types+ Pipe,+ Zero,+ Producer,+ Consumer,+ Pipeline,+ -- * Create Pipes+ {-|+ 'yield' and 'await' are the only two primitives you need to create+ 'Pipe's. Because 'Pipe' is a monad, you can assemble them using+ ordinary @do@ notation. Since 'Pipe' is also a monad transformer, you+ can use 'lift' to invoke the base monad. For example:++> check :: Pipe a a IO r+> check = forever $ do+> x <- await+> lift $ putStrLn $ "Can " ++ (show x) ++ " pass?"+> ok <- lift $ read <$> getLine+> when ok (yield x)+ -}+ await,+ yield,+ pipe,+ discard,+ -- * Compose Pipes+ {-|+ There are two possible category implementations for 'Pipe':++ ['Lazy' composition]++ * Use as little input as possible++ * Ideal for infinite input streams that never need finalization++ ['Strict' composition]++ * Use as much input as possible++ * Ideal for finite input streams that need finalization++ Both category implementations enforce the category laws:++ * Composition is associative (within each instance). This is not+ merely associativity of monadic effects, but rather true+ associativity. The result of composition produces identical+ composite 'Pipe's regardless of how you group composition.++ * 'id' is the identity 'Pipe'. Composing a 'Pipe' with 'id' returns the+ original pipe.++ Both categories prioritize downstream effects over upstream effects.+ -}+ Lazy(..),+ Strict(..),+ -- ** Compose Pipes+ {-|+ I provide convenience functions for composition that take care of+ newtype wrapping and unwrapping. For example:++> p1 <+< p2 = unLazy $ Lazy p1 <<< Lazy p2++ '<+<' and '<-<' correspond to '<<<' from "Control.Category"++ '>+>' and '>+>' correspond to '>>>' from "Control.Category"++ '<+<' and '>+>' use 'Lazy' composition (Mnemonic: + for optimistic+ evaluation)++ '<-<' and '>->' use 'Strict' composition (Mnemonic: - for pessimistic+ evaluation) ++ However, the above operators won't work with 'id' because they work on+ 'Pipe's whereas 'id' is a newtype on a 'Pipe'. However, both 'Category'+ instances share the same 'id' implementation:++> instance Category (Lazy m r) where+> id = Lazy $ pipe id+> ....+> instance Category (Strict m r) where+> id = Strict $ pipe id+> ...++ So if you need an identity 'Pipe' that works with the above convenience+ operators, you can use 'idP' which is just @pipe id@.+ -}+ (<+<),+ (>+>),+ (<-<),+ (>->),+ idP,+ -- * Run Pipes+ runPipe+ ) where++import Control.Applicative+import Control.Category+import Control.Monad+import Control.Monad.Trans+import Prelude hiding ((.), id)++{-|+ The base type for pipes++ [@a@] The type of input received from upstream pipes++ [@b@] The type of output delivered to downstream pipes++ [@m@] The base monad++ [@r@] The type of the monad's final result++ The Pipe type is partly inspired by Mario Blazevic's Coroutine in his+ concurrency article from Issue 19 of The Monad Reader and partly inspired by+ the Trace data type from "A Language Based Approach to Unifying Events and+ Threads".+-}+data Pipe a b m r =+ Pure r -- pure = Pure+ | M (m (Pipe a b m r)) -- Monad+ | Await (a -> Pipe a b m r ) -- ((->) a) Functor+ | Yield (b, Pipe a b m r ) -- ((,) b) Functor+{- I could have factored Pipe as:++data Computation f r = Pure r | F (f (Computation f r))+data PipeF a b m r = Await (a -> r) | Yield (b, r) | M (m r)+newtype Pipe a b m r = P { unP :: Computation (PipeF a b m) r }++ This makes the Functor, Applicative, and Monad instances much simpler at the+ expense of making the Category instances *much* harder to follow because of+ excessive newtype and constructor wrapping/unwrapping. Since the Category+ instance is the meat of the library, I opted to in-line PipeF into+ computation to make it much simpler. It's a shame, because the Computation+ type is very useful in its own right and I will probably create a separate+ library around it. -}++instance (Monad m) => Functor (Pipe a b m) where+ fmap f c = case c of+ Pure r -> Pure $ f r+ M mc -> M $ liftM (fmap f) mc+ Await fc -> Await $ fmap (fmap f) fc+ Yield fc -> Yield $ fmap (fmap f) fc++instance (Monad m) => Applicative (Pipe a b m) where+ pure = Pure+ f <*> x = case f of+ Pure r -> fmap r x+ M mc -> M $ liftM (<*> x) mc+ Await fc -> Await $ fmap (<*> x) fc+ Yield fc -> Yield $ fmap (<*> x) fc++instance (Monad m) => Monad (Pipe a b m) where+ return = pure+ m >>= f = case m of+ Pure r -> f r+ M mc -> M $ liftM (>>= f) mc+ Await fc -> Await $ fmap (>>= f) fc+ Yield fc -> Yield $ fmap (>>= f) fc++instance MonadTrans (Pipe a b) where lift = M . liftM pure++-- | A data type with no exposed constructors+data Zero = Zero+{- I'm not quite sure that this is the correct approach. I also considered+ using "()" or universal quantification (i.e. Producer b m r =+ forall a . Pipe a b m r). What I really want is some way to provide runPipe+ some compile-time guarantee that its argument Pipe has no residual await or+ yield statements. -}++-- | A pipe that can only produce values+type Producer b m r = Pipe Zero b m r++-- | A pipe that can only consume values+type Consumer a m r = Pipe a Zero m r++-- | A self-contained pipeline that is ready to be run+type Pipeline m r = Pipe Zero Zero m r++{-|+ Wait for input from upstream within the 'Pipe' monad:++ 'await' blocks until input is ready.+-}+await :: Pipe a b m a+await = Await Pure ++{-|+ Pass output downstream within the 'Pipe' monad:++ 'yield' blocks until the output has been received.+-}+yield :: b -> Pipe a b m ()+yield x = Yield (x, Pure ())++{-|+ Convert a pure function into a pipe++> pipe = forever $ do+> x <- await+> yield (f x)+-}+pipe :: (Monad m) => (a -> b) -> Pipe a b m r+pipe f = forever $ await >>= yield . f++-- | The 'discard' pipe silently discards all input fed to it.+discard :: (Monad m) => Pipe a b m r+discard = forever await++newtype Lazy m r a b = Lazy { unLazy :: Pipe a b m r}+newtype Strict m r a b = Strict { unStrict :: Pipe a b m r}++idP :: (Monad m) => Pipe a a m r+idP = pipe id++(<+<), (<-<) :: (Monad m) => Pipe b c m r -> Pipe a b m r -> Pipe a c m r+p1 <+< p2 = unLazy (Lazy p1 <<< Lazy p2)+p1 <-< p2 = unStrict (Strict p1 <<< Strict p2)++(>+>), (>->) :: (Monad m) => Pipe a b m r -> Pipe b c m r -> Pipe a c m r+p1 >+> p2 = unLazy (Lazy p1 >>> Lazy p2)+p1 >-> p2 = unStrict (Strict p1 >>> Strict p2)++-- These associativities help composition detect termination quickly+infixr 9 <+<, >->+infixl 9 >+>, <-<++{- If you assume id = forever $ await >>= yield, then the below are the only two+ Category instances possible. I couldn't find any other useful definition of+ id, but perhaps I'm not being creative enough. -}+instance (Monad m) => Category (Lazy m r) where+ id = Lazy $ pipe id+ Lazy p1' . Lazy p2' = Lazy $ case (p1', p2') of+ (Yield (x1, p1), p2 ) -> yield x1 >> p1 <+< p2+ (M m1 , p2 ) -> lift m1 >>= \p1 -> p1 <+< p2+ (p1 , Await f2 ) -> await >>= \x -> p1 <+< f2 x+ (p1 , M m2 ) -> lift m2 >>= \p2 -> p1 <+< p2+ (Await f1 , Yield (x2, p2)) -> f1 x2 <+< p2+ (Pure r1 , _ ) -> Pure r1+ (_ , Pure r2 ) -> Pure r2++instance (Monad m) => Category (Strict m r) where+ id = Strict $ pipe id+ Strict p1 . Strict p2 = Strict $ (p1 >> discard) <+< p2++{-|+ Run the 'Pipe' monad transformer, converting it back into the base monad++ 'runPipe' will not work on a pipe that has loose input or output ends. If+ your pipe is still generating unhandled output, handle it. I choose not to+ automatically 'discard' output for you, because that is only one of many+ ways to deal with unhandled output.+-}+runPipe :: (Monad m) => Pipeline m r -> m r+runPipe p' = case p' of+ Pure r -> return r+ M mp -> mp >>= runPipe+ -- Technically a blocked Pipe can still await+ Await f -> runPipe $ f Zero+ -- A blocked Pipe can not yield, but I include this as a precaution+ Yield (_, p) -> runPipe p
+ LICENSE view
@@ -0,0 +1,674 @@+ GNU GENERAL PUBLIC LICENSE+ Version 3, 29 June 2007++ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>+ Everyone is permitted to copy and distribute verbatim copies+ of this license document, but changing it is not allowed.++ Preamble++ The GNU General Public License is a free, copyleft license for+software and other kinds of works.++ The licenses for most software and other practical works are designed+to take away your freedom to share and change the works. By contrast,+the GNU General Public License is intended to guarantee your freedom to+share and change all versions of a program--to make sure it remains free+software for all its users. We, the Free Software Foundation, use the+GNU General Public License for most of our software; it applies also to+any other work released this way by its authors. You can apply it to+your programs, too.++ When we speak of free software, we are referring to freedom, not+price. Our General Public Licenses are designed to make sure that you+have the freedom to distribute copies of free software (and charge for+them if you wish), that you receive source code or can get it if you+want it, that you can change the software or use pieces of it in new+free programs, and that you know you can do these things.++ To protect your rights, we need to prevent others from denying you+these rights or asking you to surrender the rights. Therefore, you have+certain responsibilities if you distribute copies of the software, or if+you modify it: responsibilities to respect the freedom of others.++ For example, if you distribute copies of such a program, whether+gratis or for a fee, you must pass on to the recipients the same+freedoms that you received. You must make sure that they, too, receive+or can get the source code. And you must show them these terms so they+know their rights.++ Developers that use the GNU GPL protect your rights with two steps:+(1) assert copyright on the software, and (2) offer you this License+giving you legal permission to copy, distribute and/or modify it.++ For the developers' and authors' protection, the GPL clearly explains+that there is no warranty for this free software. For both users' and+authors' sake, the GPL requires that modified versions be marked as+changed, so that their problems will not be attributed erroneously to+authors of previous versions.++ Some devices are designed to deny users access to install or run+modified versions of the software inside them, although the manufacturer+can do so. This is fundamentally incompatible with the aim of+protecting users' freedom to change the software. The systematic+pattern of such abuse occurs in the area of products for individuals to+use, which is precisely where it is most unacceptable. Therefore, we+have designed this version of the GPL to prohibit the practice for those+products. If such problems arise substantially in other domains, we+stand ready to extend this provision to those domains in future versions+of the GPL, as needed to protect the freedom of users.++ Finally, every program is threatened constantly by software patents.+States should not allow patents to restrict development and use of+software on general-purpose computers, but in those that do, we wish to+avoid the special danger that patents applied to a free program could+make it effectively proprietary. To prevent this, the GPL assures that+patents cannot be used to render the program non-free.++ The precise terms and conditions for copying, distribution and+modification follow.++ TERMS AND CONDITIONS++ 0. Definitions.++ "This License" refers to version 3 of the GNU General Public License.++ "Copyright" also means copyright-like laws that apply to other kinds of+works, such as semiconductor masks.++ "The Program" refers to any copyrightable work licensed under this+License. Each licensee is addressed as "you". "Licensees" and+"recipients" may be individuals or organizations.++ To "modify" a work means to copy from or adapt all or part of the work+in a fashion requiring copyright permission, other than the making of an+exact copy. The resulting work is called a "modified version" of the+earlier work or a work "based on" the earlier work.++ A "covered work" means either the unmodified Program or a work based+on the Program.++ To "propagate" a work means to do anything with it that, without+permission, would make you directly or secondarily liable for+infringement under applicable copyright law, except executing it on a+computer or modifying a private copy. Propagation includes copying,+distribution (with or without modification), making available to the+public, and in some countries other activities as well.++ To "convey" a work means any kind of propagation that enables other+parties to make or receive copies. Mere interaction with a user through+a computer network, with no transfer of a copy, is not conveying.++ An interactive user interface displays "Appropriate Legal Notices"+to the extent that it includes a convenient and prominently visible+feature that (1) displays an appropriate copyright notice, and (2)+tells the user that there is no warranty for the work (except to the+extent that warranties are provided), that licensees may convey the+work under this License, and how to view a copy of this License. If+the interface presents a list of user commands or options, such as a+menu, a prominent item in the list meets this criterion.++ 1. Source Code.++ The "source code" for a work means the preferred form of the work+for making modifications to it. "Object code" means any non-source+form of a work.++ A "Standard Interface" means an interface that either is an official+standard defined by a recognized standards body, or, in the case of+interfaces specified for a particular programming language, one that+is widely used among developers working in that language.++ The "System Libraries" of an executable work include anything, other+than the work as a whole, that (a) is included in the normal form of+packaging a Major Component, but which is not part of that Major+Component, and (b) serves only to enable use of the work with that+Major Component, or to implement a Standard Interface for which an+implementation is available to the public in source code form. A+"Major Component", in this context, means a major essential component+(kernel, window system, and so on) of the specific operating system+(if any) on which the executable work runs, or a compiler used to+produce the work, or an object code interpreter used to run it.++ The "Corresponding Source" for a work in object code form means all+the source code needed to generate, install, and (for an executable+work) run the object code and to modify the work, including scripts to+control those activities. However, it does not include the work's+System Libraries, or general-purpose tools or generally available free+programs which are used unmodified in performing those activities but+which are not part of the work. For example, Corresponding Source+includes interface definition files associated with source files for+the work, and the source code for shared libraries and dynamically+linked subprograms that the work is specifically designed to require,+such as by intimate data communication or control flow between those+subprograms and other parts of the work.++ The Corresponding Source need not include anything that users+can regenerate automatically from other parts of the Corresponding+Source.++ The Corresponding Source for a work in source code form is that+same work.++ 2. Basic Permissions.++ All rights granted under this License are granted for the term of+copyright on the Program, and are irrevocable provided the stated+conditions are met. This License explicitly affirms your unlimited+permission to run the unmodified Program. The output from running a+covered work is covered by this License only if the output, given its+content, constitutes a covered work. This License acknowledges your+rights of fair use or other equivalent, as provided by copyright law.++ You may make, run and propagate covered works that you do not+convey, without conditions so long as your license otherwise remains+in force. You may convey covered works to others for the sole purpose+of having them make modifications exclusively for you, or provide you+with facilities for running those works, provided that you comply with+the terms of this License in conveying all material for which you do+not control copyright. Those thus making or running the covered works+for you must do so exclusively on your behalf, under your direction+and control, on terms that prohibit them from making any copies of+your copyrighted material outside their relationship with you.++ Conveying under any other circumstances is permitted solely under+the conditions stated below. Sublicensing is not allowed; section 10+makes it unnecessary.++ 3. Protecting Users' Legal Rights From Anti-Circumvention Law.++ No covered work shall be deemed part of an effective technological+measure under any applicable law fulfilling obligations under article+11 of the WIPO copyright treaty adopted on 20 December 1996, or+similar laws prohibiting or restricting circumvention of such+measures.++ When you convey a covered work, you waive any legal power to forbid+circumvention of technological measures to the extent such circumvention+is effected by exercising rights under this License with respect to+the covered work, and you disclaim any intention to limit operation or+modification of the work as a means of enforcing, against the work's+users, your or third parties' legal rights to forbid circumvention of+technological measures.++ 4. Conveying Verbatim Copies.++ You may convey verbatim copies of the Program's source code as you+receive it, in any medium, provided that you conspicuously and+appropriately publish on each copy an appropriate copyright notice;+keep intact all notices stating that this License and any+non-permissive terms added in accord with section 7 apply to the code;+keep intact all notices of the absence of any warranty; and give all+recipients a copy of this License along with the Program.++ You may charge any price or no price for each copy that you convey,+and you may offer support or warranty protection for a fee.++ 5. Conveying Modified Source Versions.++ You may convey a work based on the Program, or the modifications to+produce it from the Program, in the form of source code under the+terms of section 4, provided that you also meet all of these conditions:++ a) The work must carry prominent notices stating that you modified+ it, and giving a relevant date.++ b) The work must carry prominent notices stating that it is+ released under this License and any conditions added under section+ 7. This requirement modifies the requirement in section 4 to+ "keep intact all notices".++ c) You must license the entire work, as a whole, under this+ License to anyone who comes into possession of a copy. This+ License will therefore apply, along with any applicable section 7+ additional terms, to the whole of the work, and all its parts,+ regardless of how they are packaged. This License gives no+ permission to license the work in any other way, but it does not+ invalidate such permission if you have separately received it.++ d) If the work has interactive user interfaces, each must display+ Appropriate Legal Notices; however, if the Program has interactive+ interfaces that do not display Appropriate Legal Notices, your+ work need not make them do so.++ A compilation of a covered work with other separate and independent+works, which are not by their nature extensions of the covered work,+and which are not combined with it such as to form a larger program,+in or on a volume of a storage or distribution medium, is called an+"aggregate" if the compilation and its resulting copyright are not+used to limit the access or legal rights of the compilation's users+beyond what the individual works permit. Inclusion of a covered work+in an aggregate does not cause this License to apply to the other+parts of the aggregate.++ 6. Conveying Non-Source Forms.++ You may convey a covered work in object code form under the terms+of sections 4 and 5, provided that you also convey the+machine-readable Corresponding Source under the terms of this License,+in one of these ways:++ a) Convey the object code in, or embodied in, a physical product+ (including a physical distribution medium), accompanied by the+ Corresponding Source fixed on a durable physical medium+ customarily used for software interchange.++ b) Convey the object code in, or embodied in, a physical product+ (including a physical distribution medium), accompanied by a+ written offer, valid for at least three years and valid for as+ long as you offer spare parts or customer support for that product+ model, to give anyone who possesses the object code either (1) a+ copy of the Corresponding Source for all the software in the+ product that is covered by this License, on a durable physical+ medium customarily used for software interchange, for a price no+ more than your reasonable cost of physically performing this+ conveying of source, or (2) access to copy the+ Corresponding Source from a network server at no charge.++ c) Convey individual copies of the object code with a copy of the+ written offer to provide the Corresponding Source. This+ alternative is allowed only occasionally and noncommercially, and+ only if you received the object code with such an offer, in accord+ with subsection 6b.++ d) Convey the object code by offering access from a designated+ place (gratis or for a charge), and offer equivalent access to the+ Corresponding Source in the same way through the same place at no+ further charge. You need not require recipients to copy the+ Corresponding Source along with the object code. If the place to+ copy the object code is a network server, the Corresponding Source+ may be on a different server (operated by you or a third party)+ that supports equivalent copying facilities, provided you maintain+ clear directions next to the object code saying where to find the+ Corresponding Source. Regardless of what server hosts the+ Corresponding Source, you remain obligated to ensure that it is+ available for as long as needed to satisfy these requirements.++ e) Convey the object code using peer-to-peer transmission, provided+ you inform other peers where the object code and Corresponding+ Source of the work are being offered to the general public at no+ charge under subsection 6d.++ A separable portion of the object code, whose source code is excluded+from the Corresponding Source as a System Library, need not be+included in conveying the object code work.++ A "User Product" is either (1) a "consumer product", which means any+tangible personal property which is normally used for personal, family,+or household purposes, or (2) anything designed or sold for incorporation+into a dwelling. In determining whether a product is a consumer product,+doubtful cases shall be resolved in favor of coverage. For a particular+product received by a particular user, "normally used" refers to a+typical or common use of that class of product, regardless of the status+of the particular user or of the way in which the particular user+actually uses, or expects or is expected to use, the product. A product+is a consumer product regardless of whether the product has substantial+commercial, industrial or non-consumer uses, unless such uses represent+the only significant mode of use of the product.++ "Installation Information" for a User Product means any methods,+procedures, authorization keys, or other information required to install+and execute modified versions of a covered work in that User Product from+a modified version of its Corresponding Source. The information must+suffice to ensure that the continued functioning of the modified object+code is in no case prevented or interfered with solely because+modification has been made.++ If you convey an object code work under this section in, or with, or+specifically for use in, a User Product, and the conveying occurs as+part of a transaction in which the right of possession and use of the+User Product is transferred to the recipient in perpetuity or for a+fixed term (regardless of how the transaction is characterized), the+Corresponding Source conveyed under this section must be accompanied+by the Installation Information. But this requirement does not apply+if neither you nor any third party retains the ability to install+modified object code on the User Product (for example, the work has+been installed in ROM).++ The requirement to provide Installation Information does not include a+requirement to continue to provide support service, warranty, or updates+for a work that has been modified or installed by the recipient, or for+the User Product in which it has been modified or installed. Access to a+network may be denied when the modification itself materially and+adversely affects the operation of the network or violates the rules and+protocols for communication across the network.++ Corresponding Source conveyed, and Installation Information provided,+in accord with this section must be in a format that is publicly+documented (and with an implementation available to the public in+source code form), and must require no special password or key for+unpacking, reading or copying.++ 7. Additional Terms.++ "Additional permissions" are terms that supplement the terms of this+License by making exceptions from one or more of its conditions.+Additional permissions that are applicable to the entire Program shall+be treated as though they were included in this License, to the extent+that they are valid under applicable law. If additional permissions+apply only to part of the Program, that part may be used separately+under those permissions, but the entire Program remains governed by+this License without regard to the additional permissions.++ When you convey a copy of a covered work, you may at your option+remove any additional permissions from that copy, or from any part of+it. (Additional permissions may be written to require their own+removal in certain cases when you modify the work.) You may place+additional permissions on material, added by you to a covered work,+for which you have or can give appropriate copyright permission.++ Notwithstanding any other provision of this License, for material you+add to a covered work, you may (if authorized by the copyright holders of+that material) supplement the terms of this License with terms:++ a) Disclaiming warranty or limiting liability differently from the+ terms of sections 15 and 16 of this License; or++ b) Requiring preservation of specified reasonable legal notices or+ author attributions in that material or in the Appropriate Legal+ Notices displayed by works containing it; or++ c) Prohibiting misrepresentation of the origin of that material, or+ requiring that modified versions of such material be marked in+ reasonable ways as different from the original version; or++ d) Limiting the use for publicity purposes of names of licensors or+ authors of the material; or++ e) Declining to grant rights under trademark law for use of some+ trade names, trademarks, or service marks; or++ f) Requiring indemnification of licensors and authors of that+ material by anyone who conveys the material (or modified versions of+ it) with contractual assumptions of liability to the recipient, for+ any liability that these contractual assumptions directly impose on+ those licensors and authors.++ All other non-permissive additional terms are considered "further+restrictions" within the meaning of section 10. If the Program as you+received it, or any part of it, contains a notice stating that it is+governed by this License along with a term that is a further+restriction, you may remove that term. If a license document contains+a further restriction but permits relicensing or conveying under this+License, you may add to a covered work material governed by the terms+of that license document, provided that the further restriction does+not survive such relicensing or conveying.++ If you add terms to a covered work in accord with this section, you+must place, in the relevant source files, a statement of the+additional terms that apply to those files, or a notice indicating+where to find the applicable terms.++ Additional terms, permissive or non-permissive, may be stated in the+form of a separately written license, or stated as exceptions;+the above requirements apply either way.++ 8. Termination.++ You may not propagate or modify a covered work except as expressly+provided under this License. Any attempt otherwise to propagate or+modify it is void, and will automatically terminate your rights under+this License (including any patent licenses granted under the third+paragraph of section 11).++ However, if you cease all violation of this License, then your+license from a particular copyright holder is reinstated (a)+provisionally, unless and until the copyright holder explicitly and+finally terminates your license, and (b) permanently, if the copyright+holder fails to notify you of the violation by some reasonable means+prior to 60 days after the cessation.++ Moreover, your license from a particular copyright holder is+reinstated permanently if the copyright holder notifies you of the+violation by some reasonable means, this is the first time you have+received notice of violation of this License (for any work) from that+copyright holder, and you cure the violation prior to 30 days after+your receipt of the notice.++ Termination of your rights under this section does not terminate the+licenses of parties who have received copies or rights from you under+this License. If your rights have been terminated and not permanently+reinstated, you do not qualify to receive new licenses for the same+material under section 10.++ 9. Acceptance Not Required for Having Copies.++ You are not required to accept this License in order to receive or+run a copy of the Program. Ancillary propagation of a covered work+occurring solely as a consequence of using peer-to-peer transmission+to receive a copy likewise does not require acceptance. However,+nothing other than this License grants you permission to propagate or+modify any covered work. These actions infringe copyright if you do+not accept this License. Therefore, by modifying or propagating a+covered work, you indicate your acceptance of this License to do so.++ 10. Automatic Licensing of Downstream Recipients.++ Each time you convey a covered work, the recipient automatically+receives a license from the original licensors, to run, modify and+propagate that work, subject to this License. You are not responsible+for enforcing compliance by third parties with this License.++ An "entity transaction" is a transaction transferring control of an+organization, or substantially all assets of one, or subdividing an+organization, or merging organizations. If propagation of a covered+work results from an entity transaction, each party to that+transaction who receives a copy of the work also receives whatever+licenses to the work the party's predecessor in interest had or could+give under the previous paragraph, plus a right to possession of the+Corresponding Source of the work from the predecessor in interest, if+the predecessor has it or can get it with reasonable efforts.++ You may not impose any further restrictions on the exercise of the+rights granted or affirmed under this License. For example, you may+not impose a license fee, royalty, or other charge for exercise of+rights granted under this License, and you may not initiate litigation+(including a cross-claim or counterclaim in a lawsuit) alleging that+any patent claim is infringed by making, using, selling, offering for+sale, or importing the Program or any portion of it.++ 11. Patents.++ A "contributor" is a copyright holder who authorizes use under this+License of the Program or a work on which the Program is based. The+work thus licensed is called the contributor's "contributor version".++ A contributor's "essential patent claims" are all patent claims+owned or controlled by the contributor, whether already acquired or+hereafter acquired, that would be infringed by some manner, permitted+by this License, of making, using, or selling its contributor version,+but do not include claims that would be infringed only as a+consequence of further modification of the contributor version. For+purposes of this definition, "control" includes the right to grant+patent sublicenses in a manner consistent with the requirements of+this License.++ Each contributor grants you a non-exclusive, worldwide, royalty-free+patent license under the contributor's essential patent claims, to+make, use, sell, offer for sale, import and otherwise run, modify and+propagate the contents of its contributor version.++ In the following three paragraphs, a "patent license" is any express+agreement or commitment, however denominated, not to enforce a patent+(such as an express permission to practice a patent or covenant not to+sue for patent infringement). To "grant" such a patent license to a+party means to make such an agreement or commitment not to enforce a+patent against the party.++ If you convey a covered work, knowingly relying on a patent license,+and the Corresponding Source of the work is not available for anyone+to copy, free of charge and under the terms of this License, through a+publicly available network server or other readily accessible means,+then you must either (1) cause the Corresponding Source to be so+available, or (2) arrange to deprive yourself of the benefit of the+patent license for this particular work, or (3) arrange, in a manner+consistent with the requirements of this License, to extend the patent+license to downstream recipients. "Knowingly relying" means you have+actual knowledge that, but for the patent license, your conveying the+covered work in a country, or your recipient's use of the covered work+in a country, would infringe one or more identifiable patents in that+country that you have reason to believe are valid.++ If, pursuant to or in connection with a single transaction or+arrangement, you convey, or propagate by procuring conveyance of, a+covered work, and grant a patent license to some of the parties+receiving the covered work authorizing them to use, propagate, modify+or convey a specific copy of the covered work, then the patent license+you grant is automatically extended to all recipients of the covered+work and works based on it.++ A patent license is "discriminatory" if it does not include within+the scope of its coverage, prohibits the exercise of, or is+conditioned on the non-exercise of one or more of the rights that are+specifically granted under this License. You may not convey a covered+work if you are a party to an arrangement with a third party that is+in the business of distributing software, under which you make payment+to the third party based on the extent of your activity of conveying+the work, and under which the third party grants, to any of the+parties who would receive the covered work from you, a discriminatory+patent license (a) in connection with copies of the covered work+conveyed by you (or copies made from those copies), or (b) primarily+for and in connection with specific products or compilations that+contain the covered work, unless you entered into that arrangement,+or that patent license was granted, prior to 28 March 2007.++ Nothing in this License shall be construed as excluding or limiting+any implied license or other defenses to infringement that may+otherwise be available to you under applicable patent law.++ 12. No Surrender of Others' Freedom.++ If conditions are imposed on you (whether by court order, agreement or+otherwise) that contradict the conditions of this License, they do not+excuse you from the conditions of this License. If you cannot convey a+covered work so as to satisfy simultaneously your obligations under this+License and any other pertinent obligations, then as a consequence you may+not convey it at all. For example, if you agree to terms that obligate you+to collect a royalty for further conveying from those to whom you convey+the Program, the only way you could satisfy both those terms and this+License would be to refrain entirely from conveying the Program.++ 13. Use with the GNU Affero General Public License.++ Notwithstanding any other provision of this License, you have+permission to link or combine any covered work with a work licensed+under version 3 of the GNU Affero General Public License into a single+combined work, and to convey the resulting work. The terms of this+License will continue to apply to the part which is the covered work,+but the special requirements of the GNU Affero General Public License,+section 13, concerning interaction through a network will apply to the+combination as such.++ 14. Revised Versions of this License.++ The Free Software Foundation may publish revised and/or new versions of+the GNU General Public License from time to time. Such new versions will+be similar in spirit to the present version, but may differ in detail to+address new problems or concerns.++ Each version is given a distinguishing version number. If the+Program specifies that a certain numbered version of the GNU General+Public License "or any later version" applies to it, you have the+option of following the terms and conditions either of that numbered+version or of any later version published by the Free Software+Foundation. If the Program does not specify a version number of the+GNU General Public License, you may choose any version ever published+by the Free Software Foundation.++ If the Program specifies that a proxy can decide which future+versions of the GNU General Public License can be used, that proxy's+public statement of acceptance of a version permanently authorizes you+to choose that version for the Program.++ Later license versions may give you additional or different+permissions. However, no additional obligations are imposed on any+author or copyright holder as a result of your choosing to follow a+later version.++ 15. Disclaimer of Warranty.++ THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY+APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR+PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM+IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.++ 16. Limitation of Liability.++ IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF+SUCH DAMAGES.++ 17. Interpretation of Sections 15 and 16.++ If the disclaimer of warranty and limitation of liability provided+above cannot be given local legal effect according to their terms,+reviewing courts shall apply local law that most closely approximates+an absolute waiver of all civil liability in connection with the+Program, unless a warranty or assumption of liability accompanies a+copy of the Program in return for a fee.++ END OF TERMS AND CONDITIONS++ How to Apply These Terms to Your New Programs++ If you develop a new program, and you want it to be of the greatest+possible use to the public, the best way to achieve this is to make it+free software which everyone can redistribute and change under these terms.++ To do so, attach the following notices to the program. It is safest+to attach them to the start of each source file to most effectively+state the exclusion of warranty; and each file should have at least+the "copyright" line and a pointer to where the full notice is found.++ <one line to give the program's name and a brief idea of what it does.>+ Copyright (C) <year> <name of author>++ This program is free software: you can redistribute it and/or modify+ it under the terms of the GNU General Public License as published by+ the Free Software Foundation, either version 3 of the License, or+ (at your option) any later version.++ This program is distributed in the hope that it will be useful,+ but WITHOUT ANY WARRANTY; without even the implied warranty of+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the+ GNU General Public License for more details.++ You should have received a copy of the GNU General Public License+ along with this program. If not, see <http://www.gnu.org/licenses/>.++Also add information on how to contact you by electronic and paper mail.++ If the program does terminal interaction, make it output a short+notice like this when it starts in an interactive mode:++ <program> Copyright (C) <year> <name of author>+ This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.+ This is free software, and you are welcome to redistribute it+ under certain conditions; type `show c' for details.++The hypothetical commands `show w' and `show c' should show the appropriate+parts of the General Public License. Of course, your program's commands+might be different; for a GUI interface, you would use an "about box".++ You should also get your employer (if you work as a programmer) or school,+if any, to sign a "copyright disclaimer" for the program, if necessary.+For more information on this, and how to apply and follow the GNU GPL, see+<http://www.gnu.org/licenses/>.++ The GNU General Public License does not permit incorporating your program+into proprietary programs. If your program is a subroutine library, you+may consider it more useful to permit linking proprietary applications with+the library. If this is what you want to do, use the GNU Lesser General+Public License instead of this License. But first, please read+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
+ Setup.hs view
@@ -0,0 +1,2 @@+import Distribution.Simple+main = defaultMain
+ pipes.cabal view
@@ -0,0 +1,66 @@+Name: pipes+Version: 1.0+Cabal-Version: >=1.10.1+Build-Type: Simple+License: GPL+License-File: LICENSE+Copyright: 2012 Gabriel Gonzalez+Author: Gabriel Gonzalez+Maintainer: Gabriel439@gmail.com+Stability: Experimental+Bug-Reports: mailto:Gabriel439@gmail.com+Synopsis: Compositional pipelines+Description:+ \"Iteratees done right\". This library implements+ iteratees\/enumerators\/enumeratees simply and elegantly, but uses different+ naming conventions.+ .+ Advantages over traditional iteratee implementations:+ .+ * /Simpler semantics/: There is only one data type ('Pipe'), two primitives+ ('await' and 'yield'), and only one way to compose 'Pipe's ('.'). In fact,+ this library introduces no new operators, using only its 'Monad' and+ 'Category' instances to implement all behavior.+ .+ * /Clearer naming conventions/: Enumeratees are called 'Pipe's, Enumerators+ are 'Producer's, and Iteratees are 'Consumer's. 'Producer's and 'Consumer's+ are just type synonyms for 'Pipe's with either the input or output end+ closed.+ .+ * /Pipes are Categories/: You compose them using ordinary composition.+ There are actually two 'Category' instances: one for 'Lazy' composition and+ one for 'Strict' composition. Both instances satisfy the 'Category' laws.+ .+ * /Intuitive/: Pipe composition is easier to reason about because it is a true+ 'Category'. Composition works seamlessly and you don't have to worry about+ restarting iteratees, feeding new input, etc. \"It just works\".+ .+ * /"Vertical" concatenation works flawlessly on everything/: ('>>')+ concatenates 'Pipe's, but since everything is a 'Pipe', you can use it to+ concatenate 'Producer's, 'Consumer's, and even intermediate 'Pipe' stages.+ Vertical Concatenation always works the way you expect, picking up where the+ previous 'Pipe' left off.+ .+ * /Symmetric implementation/: Most iteratee libraries are either+ enumerator-driven or iteratee-driven. 'Pipe's are implemented+ symmetrically, which is why they can be composed with either 'Lazy'+ ('Consumer'-driven) or 'Strict' ('Producer'-driven) semantics.+ .+ Check out "Control.Pipe" for a copious introduction (in the spirit of the+ @iterIO@ library) and "Control.Pipe.Common" for the actual implementation.+ .+ This library does not yet provide convenience 'Pipe's for common operations,+ but they are forthcoming. However, there are several examples in the+ documentation to get you started and I encourage you to write your own to see+ how easy they are to write.+Category: Control, Enumerator+Tested-With: GHC ==7.0.3+Source-Repository head+ Type: git+ Location: https://github.com/Gabriel439/Haskell-Pipes-Library++Library+ Build-Depends: base >= 4 && < 5, mtl+ Exposed-Modules: Control.Pipe, Control.Pipe.Common+ GHC-Options: -O2+ Default-Language: Haskell2010