pipes-4.1.9/benchmarks/0000755000000000000000000000000012713420457013155 5ustar0000000000000000pipes-4.1.9/src/0000755000000000000000000000000012713420534011623 5ustar0000000000000000pipes-4.1.9/src/Pipes/0000755000000000000000000000000012713420555012706 5ustar0000000000000000pipes-4.1.9/tests/0000755000000000000000000000000012267121502012173 5ustar0000000000000000pipes-4.1.9/src/Pipes.hs0000644000000000000000000004106412713420457013250 0ustar0000000000000000{-# LANGUAGE RankNTypes , FlexibleInstances , MultiParamTypeClasses , UndecidableInstances , Trustworthy #-} {-| This module is the recommended entry point to the @pipes@ library. Read "Pipes.Tutorial" if you want a tutorial explaining how to use this library. -} module Pipes ( -- * The Proxy Monad Transformer Proxy , X , Effect , Effect' , runEffect -- ** Producers -- $producers , Producer , Producer' , yield , for , (~>) , (<~) -- ** Consumers -- $consumers , Consumer , Consumer' , await , (>~) , (~<) -- ** Pipes -- $pipes , Pipe , cat , (>->) , (<-<) -- * ListT , ListT(..) , runListT , Enumerable(..) -- * Utilities , next , each , every , discard -- * Re-exports -- $reexports , module Control.Monad , module Control.Monad.IO.Class , module Control.Monad.Trans.Class , module Control.Monad.Morph , module Data.Foldable ) where import Control.Applicative (Applicative(pure, (<*>)), Alternative(empty, (<|>))) import Control.Monad (void) import Control.Monad.Error (MonadError(..)) import Control.Monad.IO.Class (MonadIO(liftIO)) import Control.Monad (MonadPlus(mzero, mplus)) import Control.Monad.Reader (MonadReader(..)) import Control.Monad.State (MonadState(..)) import Control.Monad.Trans.Class (MonadTrans(lift)) import Control.Monad.Trans.Error (ErrorT(runErrorT)) import Control.Monad.Trans.Identity (IdentityT(runIdentityT)) import Control.Monad.Trans.Maybe (MaybeT(runMaybeT)) import Control.Monad.Writer (MonadWriter(..)) import Data.Foldable (Foldable) import Data.Monoid (Monoid(..)) import Pipes.Core import Pipes.Internal (Proxy(..)) import qualified Data.Foldable as F -- Re-exports import Control.Monad.Morph (MFunctor(hoist)) infixl 4 <~ infixr 4 ~> infixl 5 ~< infixr 5 >~ infixl 7 >-> infixr 7 <-< {- $producers Use 'yield' to produce output and ('~>') \/ 'for' to substitute 'yield's. 'yield' and ('~>') obey the 'Control.Category.Category' laws: @ \-\- Substituting \'yield\' with \'f\' gives \'f\' 'yield' '~>' f = f \-\- Substituting every \'yield\' with another \'yield\' does nothing f '~>' 'yield' = f \-\- \'yield\' substitution is associative (f '~>' g) '~>' h = f '~>' (g '~>' h) @ These are equivalent to the following \"for loop laws\": @ \-\- Looping over a single yield simplifies to function application 'for' ('yield' x) f = f x \-\- Re-yielding every element of a stream returns the original stream 'for' s 'yield' = s \-\- Nested for loops can become a sequential 'for' loops if the inner loop \-\- body ignores the outer loop variable 'for' s (\\a -\> 'for' (f a) g) = 'for' ('for' s f) g = 'for' s (f '~>' g) @ -} {-| Produce a value @ 'yield' :: 'Monad' m => a -> 'Pipe' x a m () @ -} yield :: Monad m => a -> Producer' a m () yield = respond {-# INLINABLE [1] yield #-} {-| @(for p body)@ loops over @p@ replacing each 'yield' with @body@. @ 'for' :: 'Monad' m => 'Producer' b m r -> (b -> 'Effect' m ()) -> 'Effect' m r 'for' :: 'Monad' m => 'Producer' b m r -> (b -> 'Producer' c m ()) -> 'Producer' c m r 'for' :: 'Monad' m => 'Pipe' x b m r -> (b -> 'Consumer' x m ()) -> 'Consumer' x m r 'for' :: 'Monad' m => 'Pipe' x b m r -> (b -> 'Pipe' x c m ()) -> 'Pipe' x c m r @ The following diagrams show the flow of information: @ .---> b / | +-----------+ / +-----|-----+ +---------------+ | | / | v | | | | | / | | | | x ==> p ==> b ---' x ==> body ==> c = x ==> 'for' p body ==> c | | | | | | | | | | | | | | | +-----|-----+ +-----|-----+ +-------|-------+ v v v r () r @ For a more complete diagram including bidirectional flow, see "Pipes.Core#respond-diagram". -} for :: Monad m => Proxy x' x b' b m a' -- ^ -> (b -> Proxy x' x c' c m b') -- ^ -> Proxy x' x c' c m a' for = (//>) -- There are a number of useful rewrites which can be performed on various uses -- of this combinator; to ensure that they fire we defer inlining until quite -- late. {-# INLINABLE [0] for #-} {-# RULES "for (for p f) g" forall p f g . for (for p f) g = for p (\a -> for (f a) g) ; "for p yield" forall p . for p yield = p ; "for (yield x) f" forall x f . for (yield x) f = f x ; "for cat f" forall f . for cat f = let go = do x <- await f x go in go ; "f >~ (g >~ p)" forall f g p . f >~ (g >~ p) = (f >~ g) >~ p ; "await >~ p" forall p . await >~ p = p ; "p >~ await" forall p . p >~ await = p ; "m >~ cat" forall m . m >~ cat = let go = do x <- m yield x go in go ; "p1 >-> (p2 >-> p3)" forall p1 p2 p3 . p1 >-> (p2 >-> p3) = (p1 >-> p2) >-> p3 ; "p >-> cat" forall p . p >-> cat = p ; "cat >-> p" forall p . cat >-> p = p #-} {-| Compose loop bodies @ ('~>') :: 'Monad' m => (a -> 'Producer' b m r) -> (b -> 'Effect' m ()) -> (a -> 'Effect' m r) ('~>') :: 'Monad' m => (a -> 'Producer' b m r) -> (b -> 'Producer' c m ()) -> (a -> 'Producer' c m r) ('~>') :: 'Monad' m => (a -> 'Pipe' x b m r) -> (b -> 'Consumer' x m ()) -> (a -> 'Consumer' x m r) ('~>') :: 'Monad' m => (a -> 'Pipe' x b m r) -> (b -> 'Pipe' x c m ()) -> (a -> 'Pipe' x c m r) @ The following diagrams show the flow of information: @ a .---> b a | / | | +-----|-----+ / +-----|-----+ +------|------+ | v | / | v | | v | | | / | | | | x ==> f ==> b ---' x ==> g ==> c = x ==> f '~>' g ==> c | | | | | | | | | | | | | | | +-----|-----+ +-----|-----+ +------|------+ v v v r () r @ For a more complete diagram including bidirectional flow, see "Pipes.Core#respond-diagram". -} (~>) :: Monad m => (a -> Proxy x' x b' b m a') -- ^ -> (b -> Proxy x' x c' c m b') -- ^ -> (a -> Proxy x' x c' c m a') (~>) = (/>/) {-# INLINABLE (~>) #-} -- | ('~>') with the arguments flipped (<~) :: Monad m => (b -> Proxy x' x c' c m b') -- ^ -> (a -> Proxy x' x b' b m a') -- ^ -> (a -> Proxy x' x c' c m a') g <~ f = f ~> g {-# INLINABLE (<~) #-} {- $consumers Use 'await' to request input and ('>~') to substitute 'await's. 'await' and ('>~') obey the 'Control.Category.Category' laws: @ \-\- Substituting every \'await\' with another \'await\' does nothing 'await' '>~' f = f \-\- Substituting \'await\' with \'f\' gives \'f\' f '>~' 'await' = f \-\- \'await\' substitution is associative (f '>~' g) '>~' h = f '>~' (g '>~' h) @ -} {-| Consume a value @ 'await' :: 'Monad' m => 'Pipe' a y m a @ -} await :: Monad m => Consumer' a m a await = request () {-# INLINABLE [1] await #-} {-| @(draw >~ p)@ loops over @p@ replacing each 'await' with @draw@ @ ('>~') :: 'Monad' m => 'Effect' m b -> 'Consumer' b m c -> 'Effect' m c ('>~') :: 'Monad' m => 'Consumer' a m b -> 'Consumer' b m c -> 'Consumer' a m c ('>~') :: 'Monad' m => 'Producer' y m b -> 'Pipe' b y m c -> 'Producer' y m c ('>~') :: 'Monad' m => 'Pipe' a y m b -> 'Pipe' b y m c -> 'Pipe' a y m c @ The following diagrams show the flow of information: @ +-----------+ +-----------+ +-------------+ | | | | | | | | | | | | a ==> f ==> y .---> b ==> g ==> y = a ==> f '>~' g ==> y | | / | | | | | | | / | | | | | | +-----|-----+ / +-----|-----+ +------|------+ v / v v b ----' c c @ For a more complete diagram including bidirectional flow, see "Pipes.Core#request-diagram". -} (>~) :: Monad m => Proxy a' a y' y m b -- ^ -> Proxy () b y' y m c -- ^ -> Proxy a' a y' y m c p1 >~ p2 = (\() -> p1) >\\ p2 {-# INLINABLE [1] (>~) #-} -- | ('>~') with the arguments flipped (~<) :: Monad m => Proxy () b y' y m c -- ^ -> Proxy a' a y' y m b -- ^ -> Proxy a' a y' y m c p2 ~< p1 = p1 >~ p2 {-# INLINABLE (~<) #-} {- $pipes Use 'await' and 'yield' to build 'Pipe's and ('>->') to connect 'Pipe's. 'cat' and ('>->') obey the 'Control.Category.Category' laws: @ \-\- Useless use of cat 'cat' '>->' f = f \-\- Redirecting output to cat does nothing f '>->' 'cat' = f \-\- The pipe operator is associative (f '>->' g) '>->' h = f '>->' (g '>->' h) @ -} -- | The identity 'Pipe', analogous to the Unix @cat@ program cat :: Monad m => Pipe a a m r cat = pull () {-# INLINABLE [1] cat #-} {-| 'Pipe' composition, analogous to the Unix pipe operator @ ('>->') :: 'Monad' m => 'Producer' b m r -> 'Consumer' b m r -> 'Effect' m r ('>->') :: 'Monad' m => 'Producer' b m r -> 'Pipe' b c m r -> 'Producer' c m r ('>->') :: 'Monad' m => 'Pipe' a b m r -> 'Consumer' b m r -> 'Consumer' a m r ('>->') :: 'Monad' m => 'Pipe' a b m r -> 'Pipe' b c m r -> 'Pipe' a c m r @ The following diagrams show the flow of information: @ +-----------+ +-----------+ +-------------+ | | | | | | | | | | | | a ==> f ==> b ==> g ==> c = a ==> f '>->' g ==> c | | | | | | | | | | | | | | | +-----|-----+ +-----|-----+ +------|------+ v v v r r r @ For a more complete diagram including bidirectional flow, see "Pipes.Core#pull-diagram". -} (>->) :: Monad m => Proxy a' a () b m r -- ^ -> Proxy () b c' c m r -- ^ -> Proxy a' a c' c m r p1 >-> p2 = (\() -> p1) +>> p2 {-# INLINABLE [1] (>->) #-} {-| The list monad transformer, which extends a monad with non-determinism 'return' corresponds to 'yield', yielding a single value ('>>=') corresponds to 'for', calling the second computation once for each time the first computation 'yield's. -} newtype ListT m a = Select { enumerate :: Producer a m () } instance (Monad m) => Functor (ListT m) where fmap f p = Select (for (enumerate p) (\a -> yield (f a))) instance (Monad m) => Applicative (ListT m) where pure a = Select (yield a) mf <*> mx = Select ( for (enumerate mf) (\f -> for (enumerate mx) (\x -> yield (f x) ) ) ) instance (Monad m) => Monad (ListT m) where return = pure m >>= f = Select (for (enumerate m) (\a -> enumerate (f a))) fail _ = mzero instance MonadTrans ListT where lift m = Select (do a <- lift m yield a ) instance (MonadIO m) => MonadIO (ListT m) where liftIO m = lift (liftIO m) instance (Monad m) => Alternative (ListT m) where empty = Select (return ()) p1 <|> p2 = Select (do enumerate p1 enumerate p2 ) instance (Monad m) => MonadPlus (ListT m) where mzero = empty mplus = (<|>) instance MFunctor ListT where hoist morph = Select . hoist morph . enumerate instance (Monad m) => Monoid (ListT m a) where mempty = empty mappend = (<|>) instance (MonadState s m) => MonadState s (ListT m) where get = lift get put s = lift (put s) state f = lift (state f) instance (MonadWriter w m) => MonadWriter w (ListT m) where writer = lift . writer tell w = lift (tell w) listen l = Select (go (enumerate l) mempty) where go p w = case p of Request a' fa -> Request a' (\a -> go (fa a ) w) Respond b fb' -> Respond (b, w) (\b' -> go (fb' b') w) M m -> M (do (p', w') <- listen m return (go p' $! mappend w w') ) Pure r -> Pure r pass l = Select (go (enumerate l) mempty) where go p w = case p of Request a' fa -> Request a' (\a -> go (fa a ) w) Respond (b, f) fb' -> M (pass (return (Respond b (\b' -> go (fb' b') (f w)), \_ -> f w) )) M m -> M (do (p', w') <- listen m return (go p' $! mappend w w') ) Pure r -> Pure r instance (MonadReader i m) => MonadReader i (ListT m) where ask = lift ask local f l = Select (local f (enumerate l)) reader f = lift (reader f) instance (MonadError e m) => MonadError e (ListT m) where throwError e = lift (throwError e) catchError l k = Select (catchError (enumerate l) (\e -> enumerate (k e))) -- | Run a self-contained `ListT` computation runListT :: Monad m => ListT m a -> m () runListT l = runEffect (enumerate (l >> mzero)) {-# INLINABLE runListT #-} {-| 'Enumerable' generalizes 'Data.Foldable.Foldable', converting effectful containers to 'ListT's. Instances of 'Enumerable' must satisfy these two laws: > toListT (return r) = return r > > toListT $ do x <- m = do x <- toListT m > f x toListT (f x) In other words, 'toListT' is monad morphism. -} class Enumerable t where toListT :: Monad m => t m a -> ListT m a instance Enumerable ListT where toListT = id instance Enumerable IdentityT where toListT m = Select $ do a <- lift $ runIdentityT m yield a instance Enumerable MaybeT where toListT m = Select $ do x <- lift $ runMaybeT m case x of Nothing -> return () Just a -> yield a instance Enumerable (ErrorT e) where toListT m = Select $ do x <- lift $ runErrorT m case x of Left _ -> return () Right a -> yield a {-| Consume the first value from a 'Producer' 'next' either fails with a 'Left' if the 'Producer' terminates or succeeds with a 'Right' providing the next value and the remainder of the 'Producer'. -} next :: Monad m => Producer a m r -> m (Either r (a, Producer a m r)) next = go where go p = case p of Request v _ -> closed v Respond a fu -> return (Right (a, fu ())) M m -> m >>= go Pure r -> return (Left r) {-# INLINABLE next #-} -- | Convert a 'F.Foldable' to a 'Producer' each :: (Monad m, Foldable f) => f a -> Producer' a m () each = F.foldr (\a p -> yield a >> p) (return ()) {-# INLINABLE each #-} {- The above code is the same as: > each = Data.Foldable.mapM_ yield ... except writing it directly in terms of `Data.Foldable.foldr` improves build/foldr fusion -} -- | Convert an 'Enumerable' to a 'Producer' every :: (Monad m, Enumerable t) => t m a -> Producer' a m () every it = discard >\\ enumerate (toListT it) {-# INLINABLE every #-} -- | Discards a value discard :: Monad m => a -> m () discard _ = return () {-# INLINABLE discard #-} -- | ('>->') with the arguments flipped (<-<) :: Monad m => Proxy () b c' c m r -- ^ -> Proxy a' a () b m r -- ^ -> Proxy a' a c' c m r p2 <-< p1 = p1 >-> p2 {-# INLINABLE (<-<) #-} {- $reexports "Control.Monad" re-exports 'void' "Control.Monad.IO.Class" re-exports 'MonadIO'. "Control.Monad.Trans.Class" re-exports 'MonadTrans'. "Control.Monad.Morph" re-exports 'MFunctor'. "Data.Foldable" re-exports 'Foldable' (the class name only). -} pipes-4.1.9/src/Pipes/Core.hs0000644000000000000000000005474312713420457014150 0ustar0000000000000000{-| The core functionality for the 'Proxy' monad transformer Read "Pipes.Tutorial" if you want a beginners tutorial explaining how to use this library. The documentation in this module targets more advanced users who want to understand the theory behind this library. This module is not exported by default, and I recommend you use the unidirectional operations exported by the "Pipes" module if you can. You should only use this module if you require advanced features like: * bidirectional communication, or: * push-based 'Pipe's. -} {-# LANGUAGE RankNTypes, Trustworthy #-} module Pipes.Core ( -- * Proxy Monad Transformer -- $proxy Proxy , runEffect -- * Categories -- $categories -- ** Respond -- $respond , respond , (/>/) , (//>) -- ** Request -- $request , request , (\>\) , (>\\) -- ** Push -- $push , push , (>~>) , (>>~) -- ** Pull -- $pull , pull , (>+>) , (+>>) -- ** Reflect -- $reflect , reflect -- * Concrete Type Synonyms , X , Effect , Producer , Pipe , Consumer , Client , Server -- * Polymorphic Type Synonyms , Effect' , Producer' , Consumer' , Client' , Server' -- * Flipped operators , (\<\) , (/ ==> b | | | +----|----+ v r @ You can connect proxies together in five different ways: * ('Pipes.>+>'): connect pull-based streams * ('Pipes.>~>'): connect push-based streams * ('Pipes.\>\'): chain folds * ('Pipes./>/'): chain unfolds * ('Control.Monad.>=>'): sequence proxies -} -- | Run a self-contained 'Effect', converting it back to the base monad runEffect :: Monad m => Effect m r -> m r runEffect = go where go p = case p of Request v _ -> closed v Respond v _ -> closed v M m -> m >>= go Pure r -> return r {-# INLINABLE runEffect #-} {- * Keep proxy composition lower in precedence than function composition, which is 9 at the time of of this comment, so that users can write things like: > lift . k >+> p > > hoist f . k >+> p * Keep the priorities different so that users can mix composition operators like: > up \>\ p />/ dn > > up >~> p >+> dn * Keep 'request' and 'respond' composition lower in precedence than 'pull' and 'push' composition, so that users can do: > read \>\ pull >+> writer * I arbitrarily choose a lower priority for downstream operators so that lazy pull-based computations need not evaluate upstream stages unless absolutely necessary. -} infixl 3 //> infixr 3 <\\ -- GHC will raise a parse error if either of these lines ends infixr 4 />/, >\\ -- with '\', which is why this comment is here infixl 4 \<\, //< infixl 5 \>\ -- Same thing here infixr 5 /> infixl 7 >+>, >>~ infixr 7 <+<, ~<< infixl 8 <~< infixr 8 >~> {- $categories A 'Control.Category.Category' is a set of components that you can connect with a composition operator, ('Control.Category..'), that has an identity, 'Control.Category.id'. The ('Control.Category..') and 'Control.Category.id' must satisfy the following three 'Control.Category.Category' laws: @ \-\- Left identity 'Control.Category.id' 'Control.Category..' f = f \-\- Right identity f 'Control.Category..' 'Control.Category.id' = f \-\- Associativity (f 'Control.Category..' g) 'Control.Category..' h = f 'Control.Category..' (g 'Control.Category..' h) @ The 'Proxy' type sits at the intersection of five separate categories, four of which are named after their identity: @ Identity | Composition | Point-ful +-------------+-------------+-------------+ respond category | 'respond' | '/>/' | '//>' | request category | 'request' | '\>\' | '>\\' | push category | 'push' | '>~>' | '>>~' | pull category | 'pull' | '>+>' | '+>>' | Kleisli category | 'return' | 'Control.Monad.>=>' | '>>=' | +-------------+-------------+-------------+ @ Each composition operator has a \"point-ful\" version, analogous to how ('>>=') is the point-ful version of ('Control.Monad.>=>'). For example, ('//>') is the point-ful version of ('/>/'). The convention is that the odd character out faces the argument that is a function. -} {- $respond The 'respond' category closely corresponds to the generator design pattern. The 'respond' category obeys the category laws, where 'respond' is the identity and ('/>/') is composition: @ \-\- Left identity 'respond' '/>/' f = f \-\- Right identity f '/>/' 'respond' = f \-\- Associativity (f '/>/' g) '/>/' h = f '/>/' (g '/>/' h) @ #respond-diagram# The following diagrams show the flow of information: @ 'respond' :: 'Monad' m => a -> 'Proxy' x' x a' a m a' \ a | +----|----+ | | | x' <== \\ /==== a' | X | x ==> / \\===> a | | | +----|----+ v a' ('/>/') :: 'Monad' m => (a -> 'Proxy' x' x b' b m a') -> (b -> 'Proxy' x' x c' c m b') -> (a -> 'Proxy' x' x c' c m a') \ a /===> b a | / | | +----|----+ / +----|----+ +----|----+ | v | / | v | | v | x' <== <== b' <==\\ / x'<== <== c' x' <== <== c' | f | X | g | = | f '/>/' g | x ==> ==> b ===/ \\ x ==> ==> c x ==> ==> c' | | | \\ | | | | | | +----|----+ \\ +----|----+ +----|----+ v \\ v v a' \\==== b' a' ('//>') :: 'Monad' m => 'Proxy' x' x b' b m a' -> (b -> 'Proxy' x' x c' c m b') -> 'Proxy' x' x c' c m a' \ /===> b / | +---------+ / +----|----+ +---------+ | | / | v | | | x' <== <== b' <==\\ / x'<== <== c' x' <== <== c' | f | X | g | = | f '//>' g | x ==> ==> b ===/ \\ x ==> ==> c x ==> ==> c' | | | \\ | | | | | | +----|----+ \\ +----|----+ +----|----+ v \\ v v a' \\==== b' a' @ -} {-| Send a value of type @a@ downstream and block waiting for a reply of type @a'@ 'respond' is the identity of the respond category. -} respond :: Monad m => a -> Proxy x' x a' a m a' respond a = Respond a Pure {-# INLINABLE [1] respond #-} {-| Compose two unfolds, creating a new unfold @ (f '/>/' g) x = f x '//>' g @ ('/>/') is the composition operator of the respond category. -} (/>/) :: Monad m => (a -> Proxy x' x b' b m a') -- ^ -> (b -> Proxy x' x c' c m b') -- ^ -> (a -> Proxy x' x c' c m a') -- ^ (fa />/ fb) a = fa a //> fb {-# INLINABLE (/>/) #-} {-| @(p \/\/> f)@ replaces each 'respond' in @p@ with @f@. Point-ful version of ('/>/') -} (//>) :: Monad m => Proxy x' x b' b m a' -- ^ -> (b -> Proxy x' x c' c m b') -- ^ -> Proxy x' x c' c m a' -- ^ p0 //> fb = go p0 where go p = case p of Request x' fx -> Request x' (\x -> go (fx x)) Respond b fb' -> fb b >>= \b' -> go (fb' b') M m -> M (m >>= \p' -> return (go p')) Pure a -> Pure a {-# INLINE [1] (//>) #-} {-# RULES "(Request x' fx ) //> fb" forall x' fx fb . (Request x' fx ) //> fb = Request x' (\x -> fx x //> fb); "(Respond b fb') //> fb" forall b fb' fb . (Respond b fb') //> fb = fb b >>= \b' -> fb' b' //> fb; "(M m ) //> fb" forall m fb . (M m ) //> fb = M (m >>= \p' -> return (p' //> fb)); "(Pure a ) //> fb" forall a fb . (Pure a ) //> fb = Pure a; #-} {- $request The 'request' category closely corresponds to the iteratee design pattern. The 'request' category obeys the category laws, where 'request' is the identity and ('\>\') is composition: @ -- Left identity 'request' '\>\' f = f \-\- Right identity f '\>\' 'request' = f \-\- Associativity (f '\>\' g) '\>\' h = f '\>\' (g '\>\' h) @ #request-diagram# The following diagrams show the flow of information: @ 'request' :: 'Monad' m => a' -> 'Proxy' a' a y' y m a \ a' | +----|----+ | | | a' <=====/ <== y' | | a ======\\ ==> y | | | +----|----+ v a ('\>\') :: 'Monad' m => (b' -> 'Proxy' a' a y' y m b) -> (c' -> 'Proxy' b' b y' y m c) -> (c' -> 'Proxy' a' a y' y m c) \ b'<=====\\ c' c' | \\ | | +----|----+ \\ +----|----+ +----|----+ | v | \\ | v | | v | a' <== <== y' \\== b' <== <== y' a' <== <== y' | f | | g | = | f '\>\' g | a ==> ==> y /=> b ==> ==> y a ==> ==> y | | | / | | | | | | +----|----+ / +----|----+ +----|----+ v / v v b ======/ c c ('>\\') :: Monad m => (b' -> Proxy a' a y' y m b) -> Proxy b' b y' y m c -> Proxy a' a y' y m c \ b'<=====\\ | \\ +----|----+ \\ +---------+ +---------+ | v | \\ | | | | a' <== <== y' \\== b' <== <== y' a' <== <== y' | f | | g | = | f '>\\' g | a ==> ==> y /=> b ==> ==> y a ==> ==> y | | | / | | | | | | +----|----+ / +----|----+ +----|----+ v / v v b ======/ c c @ -} {-| Send a value of type @a'@ upstream and block waiting for a reply of type @a@ 'request' is the identity of the request category. -} request :: Monad m => a' -> Proxy a' a y' y m a request a' = Request a' Pure {-# INLINABLE [1] request #-} {-| Compose two folds, creating a new fold @ (f '\>\' g) x = f '>\\' g x @ ('\>\') is the composition operator of the request category. -} (\>\) :: Monad m => (b' -> Proxy a' a y' y m b) -- ^ -> (c' -> Proxy b' b y' y m c) -- ^ -> (c' -> Proxy a' a y' y m c) -- ^ (fb' \>\ fc') c' = fb' >\\ fc' c' {-# INLINABLE (\>\) #-} {-| @(f >\\\\ p)@ replaces each 'request' in @p@ with @f@. Point-ful version of ('\>\') -} (>\\) :: Monad m => (b' -> Proxy a' a y' y m b) -- ^ -> Proxy b' b y' y m c -- ^ -> Proxy a' a y' y m c -- ^ fb' >\\ p0 = go p0 where go p = case p of Request b' fb -> fb' b' >>= \b -> go (fb b) Respond x fx' -> Respond x (\x' -> go (fx' x')) M m -> M (m >>= \p' -> return (go p')) Pure a -> Pure a {-# INLINE [1] (>\\) #-} {-# RULES "fb' >\\ (Request b' fb )" forall fb' b' fb . fb' >\\ (Request b' fb ) = fb' b' >>= \b -> fb' >\\ fb b; "fb' >\\ (Respond x fx')" forall fb' x fx' . fb' >\\ (Respond x fx') = Respond x (\x' -> fb' >\\ fx' x'); "fb' >\\ (M m )" forall fb' m . fb' >\\ (M m ) = M (m >>= \p' -> return (fb' >\\ p')); "fb' >\\ (Pure a )" forall fb' a . fb' >\\ (Pure a ) = Pure a; #-} {- $push The 'push' category closely corresponds to push-based Unix pipes. The 'push' category obeys the category laws, where 'push' is the identity and ('>~>') is composition: @ \-\- Left identity 'push' '>~>' f = f \-\- Right identity f '>~>' 'push' = f \-\- Associativity (f '>~>' g) '>~>' h = f '>~>' (g '>~>' h) @ The following diagram shows the flow of information: @ 'push' :: 'Monad' m => a -> 'Proxy' a' a a' a m r \ a | +----|----+ | v | a' <============ a' | | a ============> a | | | +----|----+ v r ('>~>') :: 'Monad' m => (a -> 'Proxy' a' a b' b m r) -> (b -> 'Proxy' b' b c' c m r) -> (a -> 'Proxy' a' a c' c m r) \ a b a | | | +----|----+ +----|----+ +----|----+ | v | | v | | v | a' <== <== b' <== <== c' a' <== <== c' | f | | g | = | f '>~>' g | a ==> ==> b ==> ==> c a ==> ==> c | | | | | | | | | +----|----+ +----|----+ +----|----+ v v v r r r @ -} {-| Forward responses followed by requests @ 'push' = 'respond' 'Control.Monad.>=>' 'request' 'Control.Monad.>=>' 'push' @ 'push' is the identity of the push category. -} push :: Monad m => a -> Proxy a' a a' a m r push = go where go a = Respond a (\a' -> Request a' go) {-# INLINABLE [1] push #-} {-| Compose two proxies blocked while 'request'ing data, creating a new proxy blocked while 'request'ing data @ (f '>~>' g) x = f x '>>~' g @ ('>~>') is the composition operator of the push category. -} (>~>) :: Monad m => (_a -> Proxy a' a b' b m r) -- ^ -> ( b -> Proxy b' b c' c m r) -- ^ -> (_a -> Proxy a' a c' c m r) -- ^ (fa >~> fb) a = fa a >>~ fb {-# INLINABLE (>~>) #-} {-| @(p >>~ f)@ pairs each 'respond' in @p@ with a 'request' in @f@. Point-ful version of ('>~>') -} (>>~) :: Monad m => Proxy a' a b' b m r -- ^ -> (b -> Proxy b' b c' c m r) -- ^ -> Proxy a' a c' c m r -- ^ p >>~ fb = case p of Request a' fa -> Request a' (\a -> fa a >>~ fb) Respond b fb' -> fb' +>> fb b M m -> M (m >>= \p' -> return (p' >>~ fb)) Pure r -> Pure r {-# INLINE [1] (>>~) #-} {- $pull The 'pull' category closely corresponds to pull-based Unix pipes. The 'pull' category obeys the category laws, where 'pull' is the identity and ('>+>') is composition: @ \-\- Left identity 'pull' '>+>' f = f \-\- Right identity f '>+>' 'pull' = f \-\- Associativity (f '>+>' g) '>+>' h = f '>+>' (g '>+>' h) @ #pull-diagram# The following diagrams show the flow of information: @ 'pull' :: 'Monad' m => a' -> 'Proxy' a' a a' a m r \ a' | +----|----+ | v | a' <============ a' | | a ============> a | | | +----|----+ v r ('>+>') :: 'Monad' m -> (b' -> 'Proxy' a' a b' b m r) -> (c' -> 'Proxy' b' b c' c m r) -> (c' -> 'Proxy' a' a c' c m r) \ b' c' c' | | | +----|----+ +----|----+ +----|----+ | v | | v | | v | a' <== <== b' <== <== c' a' <== <== c' | f | | g | = | f >+> g | a ==> ==> b ==> ==> c a ==> ==> c | | | | | | | | | +----|----+ +----|----+ +----|----+ v v v r r r @ -} {-| Forward requests followed by responses: @ 'pull' = 'request' 'Control.Monad.>=>' 'respond' 'Control.Monad.>=>' 'pull' @ 'pull' is the identity of the pull category. -} pull :: Monad m => a' -> Proxy a' a a' a m r pull = go where go a' = Request a' (\a -> Respond a go) {-# INLINABLE [1] pull #-} {-| Compose two proxies blocked in the middle of 'respond'ing, creating a new proxy blocked in the middle of 'respond'ing @ (f '>+>' g) x = f '+>>' g x @ ('>+>') is the composition operator of the pull category. -} (>+>) :: Monad m => ( b' -> Proxy a' a b' b m r) -- ^ -> (_c' -> Proxy b' b c' c m r) -- ^ -> (_c' -> Proxy a' a c' c m r) -- ^ (fb' >+> fc') c' = fb' +>> fc' c' {-# INLINABLE (>+>) #-} {-| @(f +>> p)@ pairs each 'request' in @p@ with a 'respond' in @f@. Point-ful version of ('>+>') -} (+>>) :: Monad m => (b' -> Proxy a' a b' b m r) -- ^ -> Proxy b' b c' c m r -- ^ -> Proxy a' a c' c m r -- ^ fb' +>> p = case p of Request b' fb -> fb' b' >>~ fb Respond c fc' -> Respond c (\c' -> fb' +>> fc' c') M m -> M (m >>= \p' -> return (fb' +>> p')) Pure r -> Pure r {-# INLINABLE [1] (+>>) #-} {- $reflect @(reflect .)@ transforms each streaming category into its dual: * The request category is the dual of the respond category @ 'reflect' '.' 'respond' = 'request' 'reflect' '.' (f '/>/' g) = 'reflect' '.' f '/\' g) = 'reflect' '.' f '\<\' 'reflect' '.' g @ * The pull category is the dual of the push category @ 'reflect' '.' 'push' = 'pull' 'reflect' '.' (f '>~>' g) = 'reflect' '.' f '<+<' 'reflect' '.' g @ @ 'reflect' '.' 'pull' = 'push' 'reflect' '.' (f '>+>' g) = 'reflect' '.' f '<~<' 'reflect' '.' g @ -} -- | Switch the upstream and downstream ends reflect :: Monad m => Proxy a' a b' b m r -> Proxy b b' a a' m r reflect = go where go p = case p of Request a' fa -> Respond a' (\a -> go (fa a )) Respond b fb' -> Request b (\b' -> go (fb' b')) M m -> M (m >>= \p' -> return (go p')) Pure r -> Pure r {-# INLINABLE reflect #-} {-| An effect in the base monad 'Effect's neither 'Pipes.await' nor 'Pipes.yield' -} type Effect = Proxy X () () X -- | 'Producer's can only 'Pipes.yield' type Producer b = Proxy X () () b -- | 'Pipe's can both 'Pipes.await' and 'Pipes.yield' type Pipe a b = Proxy () a () b -- | 'Consumer's can only 'Pipes.await' type Consumer a = Proxy () a () X {-| @Client a' a@ sends requests of type @a'@ and receives responses of type @a@. 'Client's only 'request' and never 'respond'. -} type Client a' a = Proxy a' a () X {-| @Server b' b@ receives requests of type @b'@ and sends responses of type @b@. 'Server's only 'respond' and never 'request'. -} type Server b' b = Proxy X () b' b -- | Like 'Effect', but with a polymorphic type type Effect' m r = forall x' x y' y . Proxy x' x y' y m r -- | Like 'Producer', but with a polymorphic type type Producer' b m r = forall x' x . Proxy x' x () b m r -- | Like 'Consumer', but with a polymorphic type type Consumer' a m r = forall y' y . Proxy () a y' y m r -- | Like 'Server', but with a polymorphic type type Server' b' b m r = forall x' x . Proxy x' x b' b m r -- | Like 'Client', but with a polymorphic type type Client' a' a m r = forall y' y . Proxy a' a y' y m r -- | Equivalent to ('/>/') with the arguments flipped (\<\) :: Monad m => (b -> Proxy x' x c' c m b') -- ^ -> (a -> Proxy x' x b' b m a') -- ^ -> (a -> Proxy x' x c' c m a') -- ^ p1 \<\ p2 = p2 />/ p1 {-# INLINABLE (\<\) #-} -- | Equivalent to ('\>\') with the arguments flipped (/ (c' -> Proxy b' b x' x m c) -- ^ -> (b' -> Proxy a' a x' x m b) -- ^ -> (c' -> Proxy a' a x' x m c) -- ^ p1 /\ p1 {-# INLINABLE (/~>') with the arguments flipped (<~<) :: Monad m => (b -> Proxy b' b c' c m r) -- ^ -> (a -> Proxy a' a b' b m r) -- ^ -> (a -> Proxy a' a c' c m r) -- ^ p1 <~< p2 = p2 >~> p1 {-# INLINABLE (<~<) #-} -- | Equivalent to ('>+>') with the arguments flipped (<+<) :: Monad m => (c' -> Proxy b' b c' c m r) -- ^ -> (b' -> Proxy a' a b' b m r) -- ^ -> (c' -> Proxy a' a c' c m r) -- ^ p1 <+< p2 = p2 >+> p1 {-# INLINABLE (<+<) #-} -- | Equivalent to ('//>') with the arguments flipped (<\\) :: Monad m => (b -> Proxy x' x c' c m b') -- ^ -> Proxy x' x b' b m a' -- ^ -> Proxy x' x c' c m a' -- ^ f <\\ p = p //> f {-# INLINABLE (<\\) #-} -- | Equivalent to ('>\\') with the arguments flipped (//<) :: Monad m => Proxy b' b y' y m c -- ^ -> (b' -> Proxy a' a y' y m b) -- ^ -> Proxy a' a y' y m c -- ^ p //< f = f >\\ p {-# INLINABLE (//<) #-} -- | Equivalent to ('>>~') with the arguments flipped (~<<) :: Monad m => (b -> Proxy b' b c' c m r) -- ^ -> Proxy a' a b' b m r -- ^ -> Proxy a' a c' c m r -- ^ k ~<< p = p >>~ k {-# INLINABLE (~<<) #-} -- | Equivalent to ('+>>') with the arguments flipped (<<+) :: Monad m => Proxy b' b c' c m r -- ^ -> (b' -> Proxy a' a b' b m r) -- ^ -> Proxy a' a c' c m r -- ^ k <<+ p = p +>> k {-# INLINABLE (<<+) #-} {-# RULES "(p //> f) //> g" forall p f g . (p //> f) //> g = p //> (\x -> f x //> g) ; "p //> respond" forall p . p //> respond = p ; "respond x //> f" forall x f . respond x //> f = f x ; "f >\\ (g >\\ p)" forall f g p . f >\\ (g >\\ p) = (\x -> f >\\ g x) >\\ p ; "request >\\ p" forall p . request >\\ p = p ; "f >\\ request x" forall f x . f >\\ request x = f x ; "(p >>~ f) >>~ g" forall p f g . (p >>~ f) >>~ g = p >>~ (\x -> f x >>~ g) ; "p >>~ push" forall p . p >>~ push = p ; "push x >>~ f" forall x f . push x >>~ f = f x ; "f +>> (g +>> p)" forall f g p . f +>> (g +>> p) = (\x -> f +>> g x) +>> p ; "pull +>> p" forall p . pull +>> p = p ; "f +>> pull x" forall f x . f +>> pull x = f x #-} pipes-4.1.9/src/Pipes/Internal.hs0000644000000000000000000002146012656021257015023 0ustar0000000000000000{-| This is an internal module, meaning that it is unsafe to import unless you understand the risks. This module provides a fast implementation by weakening the monad transformer laws. These laws do not hold if you can pattern match on the constructors, as the following counter-example illustrates: @ 'lift' '.' 'return' = 'M' '.' 'return' '.' 'Pure' 'return' = 'Pure' 'lift' '.' 'return' /= 'return' @ You do not need to worry about this if you do not import this module, since the other modules in this library do not export the constructors or export any functions which can violate the monad transformer laws. -} {-# LANGUAGE FlexibleInstances , MultiParamTypeClasses , RankNTypes , UndecidableInstances , Trustworthy #-} module Pipes.Internal ( -- * Internal Proxy(..) , unsafeHoist , observe , X , closed ) where import Control.Applicative ( Applicative(pure, (<*>), (*>)), Alternative(empty, (<|>)) ) import Control.Monad (MonadPlus(..)) import Control.Monad.IO.Class (MonadIO(liftIO)) import Control.Monad.Trans.Class (MonadTrans(lift)) import Control.Monad.Morph (MFunctor(hoist), MMonad(embed)) import Control.Monad.Error (MonadError(..)) import Control.Monad.Reader (MonadReader(..)) import Control.Monad.State (MonadState(..)) import Control.Monad.Writer (MonadWriter(..)) import Data.Monoid (Monoid(mempty,mappend)) {-| A 'Proxy' is a monad transformer that receives and sends information on both an upstream and downstream interface. The type variables signify: * @a'@ and @a@ - The upstream interface, where @(a')@s go out and @(a)@s come in * @b'@ and @b@ - The downstream interface, where @(b)@s go out and @(b')@s come in * @m @ - The base monad * @r @ - The return value -} data Proxy a' a b' b m r = Request a' (a -> Proxy a' a b' b m r ) | Respond b (b' -> Proxy a' a b' b m r ) | M (m (Proxy a' a b' b m r)) | Pure r instance Monad m => Functor (Proxy a' a b' b m) where fmap f p0 = go p0 where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) M m -> M (m >>= \p' -> return (go p')) Pure r -> Pure (f r) instance Monad m => Applicative (Proxy a' a b' b m) where pure = Pure pf <*> px = go pf where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) M m -> M (m >>= \p' -> return (go p')) Pure f -> fmap f px m *> k = m >>= (\_ -> k) instance Monad m => Monad (Proxy a' a b' b m) where return = pure (>>=) = _bind _bind :: Monad m => Proxy a' a b' b m r -> (r -> Proxy a' a b' b m r') -> Proxy a' a b' b m r' p0 `_bind` f = go p0 where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) M m -> M (m >>= \p' -> return (go p')) Pure r -> f r {-# RULES "_bind (Request a' k) f" forall a' k f . _bind (Request a' k) f = Request a' (\a -> _bind (k a) f); "_bind (Respond b k) f" forall b k f . _bind (Respond b k) f = Respond b (\b' -> _bind (k b') f); "_bind (M m) f" forall m f . _bind (M m) f = M (m >>= \p -> return (_bind p f)); "_bind (Pure r ) f" forall r f . _bind (Pure r ) f = f r; #-} instance (Monad m, Monoid r) => Monoid (Proxy a' a b' b m r) where mempty = Pure mempty mappend p1 p2 = go p1 where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) M m -> M (m >>= \p' -> return (go p')) Pure r1 -> fmap (mappend r1) p2 instance MonadTrans (Proxy a' a b' b) where lift m = M (m >>= \r -> return (Pure r)) {-| 'unsafeHoist' is like 'hoist', but faster. This is labeled as unsafe because you will break the monad transformer laws if you do not pass a monad morphism as the first argument. This function is safe if you pass a monad morphism as the first argument. -} unsafeHoist :: Monad m => (forall x . m x -> n x) -> Proxy a' a b' b m r -> Proxy a' a b' b n r unsafeHoist nat = go where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) M m -> M (nat (m >>= \p' -> return (go p'))) Pure r -> Pure r {-# INLINABLE unsafeHoist #-} instance MFunctor (Proxy a' a b' b) where hoist nat p0 = go (observe p0) where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) M m -> M (nat (m >>= \p' -> return (go p'))) Pure r -> Pure r instance MMonad (Proxy a' a b' b) where embed f = go where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) M m -> f m >>= go Pure r -> Pure r instance MonadIO m => MonadIO (Proxy a' a b' b m) where liftIO m = M (liftIO (m >>= \r -> return (Pure r))) instance MonadReader r m => MonadReader r (Proxy a' a b' b m) where ask = lift ask local f = go where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) Pure r -> Pure r M m -> M (local f m >>= \r -> return (go r)) reader = lift . reader instance MonadState s m => MonadState s (Proxy a' a b' b m) where get = lift get put = lift . put state = lift . state instance MonadWriter w m => MonadWriter w (Proxy a' a b' b m) where writer = lift . writer tell = lift . tell listen p0 = go p0 mempty where go p w = case p of Request a' fa -> Request a' (\a -> go (fa a ) w) Respond b fb' -> Respond b (\b' -> go (fb' b') w) M m -> M (do (p', w') <- listen m return (go p' $! mappend w w') ) Pure r -> Pure (r, w) pass p0 = go p0 mempty where go p w = case p of Request a' fa -> Request a' (\a -> go (fa a ) w) Respond b fb' -> Respond b (\b' -> go (fb' b') w) M m -> M (do (p', w') <- listen m return (go p' $! mappend w w') ) Pure (r, f) -> M (pass (return (Pure r, \_ -> f w))) instance MonadError e m => MonadError e (Proxy a' a b' b m) where throwError = lift . throwError catchError p0 f = go p0 where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) Pure r -> Pure r M m -> M ((do p' <- m return (go p') ) `catchError` (\e -> return (f e)) ) instance MonadPlus m => Alternative (Proxy a' a b' b m) where empty = mzero (<|>) = mplus instance MonadPlus m => MonadPlus (Proxy a' a b' b m) where mzero = lift mzero mplus p0 p1 = go p0 where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) Pure r -> Pure r M m -> M ((do p' <- m return (go p') ) `mplus` return p1 ) {-| The monad transformer laws are correct when viewed through the 'observe' function: @ 'observe' ('lift' ('return' r)) = 'observe' ('return' r) 'observe' ('lift' (m '>>=' f)) = 'observe' ('lift' m '>>=' 'lift' '.' f) @ This correctness comes at a small cost to performance, so use this function sparingly. This function is a convenience for low-level @pipes@ implementers. You do not need to use 'observe' if you stick to the safe API. -} observe :: Monad m => Proxy a' a b' b m r -> Proxy a' a b' b m r observe p0 = M (go p0) where go p = case p of Request a' fa -> return (Request a' (\a -> observe (fa a ))) Respond b fb' -> return (Respond b (\b' -> observe (fb' b'))) M m' -> m' >>= go Pure r -> return (Pure r) {-# INLINABLE observe #-} {-| The empty type, used to close output ends When @Data.Void@ is merged into @base@, this will change to: > type X = Void -} newtype X = X X -- | Use 'closed' to \"handle\" impossible outputs closed :: X -> a closed (X x) = closed x {-# INLINABLE closed #-} pipes-4.1.9/src/Pipes/Lift.hs0000644000000000000000000002362412272655427014157 0ustar0000000000000000{-| Many actions in base monad transformers cannot be automatically 'Control.Monad.Trans.Class.lift'ed. These functions lift these remaining actions so that they work in the 'Proxy' monad transformer. See the mini-tutorial at the bottom of this module for example code and typical use cases where this module will come in handy. -} module Pipes.Lift ( -- * Utilities distribute -- * ErrorT , errorP , runErrorP , catchError , liftCatchError -- * MaybeT , maybeP , runMaybeP -- * ReaderT , readerP , runReaderP -- * StateT , stateP , runStateP , evalStateP , execStateP -- * WriterT -- $writert , writerP , runWriterP , execWriterP -- * RWST , rwsP , runRWSP , evalRWSP , execRWSP -- * Tutorial -- $tutorial ) where import Control.Monad.Trans.Class (lift, MonadTrans(..)) import qualified Control.Monad.Trans.Error as E import qualified Control.Monad.Trans.Maybe as M import qualified Control.Monad.Trans.Reader as R import qualified Control.Monad.Trans.State.Strict as S import qualified Control.Monad.Trans.Writer.Strict as W import qualified Control.Monad.Trans.RWS.Strict as RWS import Data.Monoid (Monoid) import Pipes.Internal (Proxy(..), unsafeHoist) import Control.Monad.Morph (hoist, MFunctor(..)) import Pipes.Core (runEffect, request, respond, (//>), (>\\)) -- | Distribute 'Proxy' over a monad transformer distribute :: ( Monad m , MonadTrans t , MFunctor t , Monad (t m) , Monad (t (Proxy a' a b' b m)) ) => Proxy a' a b' b (t m) r -- ^ -> t (Proxy a' a b' b m) r -- ^ distribute p = runEffect $ request' >\\ unsafeHoist (hoist lift) p //> respond' where request' = lift . lift . request respond' = lift . lift . respond {-# INLINABLE distribute #-} -- | Wrap the base monad in 'E.ErrorT' errorP :: (Monad m, E.Error e) => Proxy a' a b' b m (Either e r) -> Proxy a' a b' b (E.ErrorT e m) r errorP p = do x <- unsafeHoist lift p lift $ E.ErrorT (return x) {-# INLINABLE errorP #-} -- | Run 'E.ErrorT' in the base monad runErrorP :: (Monad m, E.Error e) => Proxy a' a b' b (E.ErrorT e m) r -> Proxy a' a b' b m (Either e r) runErrorP = E.runErrorT . distribute {-# INLINABLE runErrorP #-} -- | Catch an error in the base monad catchError :: (Monad m, E.Error e) => Proxy a' a b' b (E.ErrorT e m) r -- ^ -> (e -> Proxy a' a b' b (E.ErrorT e m) r) -- ^ -> Proxy a' a b' b (E.ErrorT e m) r catchError e h = errorP . E.runErrorT $ E.catchError (distribute e) (distribute . h) {-# INLINABLE catchError #-} -- | Catch an error using a catch function for the base monad liftCatchError :: Monad m => ( m (Proxy a' a b' b m r) -> (e -> m (Proxy a' a b' b m r)) -> m (Proxy a' a b' b m r) ) -- ^ -> (Proxy a' a b' b m r -> (e -> Proxy a' a b' b m r) -> Proxy a' a b' b m r) -- ^ liftCatchError c p0 f = go p0 where go p = case p of Request a' fa -> Request a' (\a -> go (fa a )) Respond b fb' -> Respond b (\b' -> go (fb' b')) Pure r -> Pure r M m -> M ((do p' <- m return (go p') ) `c` (\e -> return (f e)) ) {-# INLINABLE liftCatchError #-} -- | Wrap the base monad in 'M.MaybeT' maybeP :: Monad m => Proxy a' a b' b m (Maybe r) -> Proxy a' a b' b (M.MaybeT m) r maybeP p = do x <- unsafeHoist lift p lift $ M.MaybeT (return x) {-# INLINABLE maybeP #-} -- | Run 'M.MaybeT' in the base monad runMaybeP :: Monad m => Proxy a' a b' b (M.MaybeT m) r -> Proxy a' a b' b m (Maybe r) runMaybeP p = M.runMaybeT $ distribute p {-# INLINABLE runMaybeP #-} -- | Wrap the base monad in 'R.ReaderT' readerP :: Monad m => (i -> Proxy a' a b' b m r) -> Proxy a' a b' b (R.ReaderT i m) r readerP k = do i <- lift R.ask unsafeHoist lift (k i) {-# INLINABLE readerP #-} -- | Run 'R.ReaderT' in the base monad runReaderP :: Monad m => i -> Proxy a' a b' b (R.ReaderT i m) r -> Proxy a' a b' b m r runReaderP r p = (`R.runReaderT` r) $ distribute p {-# INLINABLE runReaderP #-} -- | Wrap the base monad in 'S.StateT' stateP :: Monad m => (s -> Proxy a' a b' b m (r, s)) -> Proxy a' a b' b (S.StateT s m) r stateP k = do s <- lift S.get (r, s') <- unsafeHoist lift (k s) lift (S.put s') return r {-# INLINABLE stateP #-} -- | Run 'S.StateT' in the base monad runStateP :: Monad m => s -> Proxy a' a b' b (S.StateT s m) r -> Proxy a' a b' b m (r, s) runStateP s p = (`S.runStateT` s) $ distribute p {-# INLINABLE runStateP #-} -- | Evaluate 'S.StateT' in the base monad evalStateP :: Monad m => s -> Proxy a' a b' b (S.StateT s m) r -> Proxy a' a b' b m r evalStateP s p = fmap fst $ runStateP s p {-# INLINABLE evalStateP #-} -- | Execute 'S.StateT' in the base monad execStateP :: Monad m => s -> Proxy a' a b' b (S.StateT s m) r -> Proxy a' a b' b m s execStateP s p = fmap snd $ runStateP s p {-# INLINABLE execStateP #-} {- $writert Note that 'runWriterP' and 'execWriterP' will keep the accumulator in weak-head-normal form so that folds run in constant space when possible. This means that until @transformers@ adds a truly strict 'W.WriterT', you should consider unwrapping 'W.WriterT' first using 'runWriterP' or 'execWriterP' before running your 'Proxy'. You will get better performance this way and eliminate space leaks if your accumulator doesn't have any lazy fields. -} -- | Wrap the base monad in 'W.WriterT' writerP :: (Monad m, Monoid w) => Proxy a' a b' b m (r, w) -> Proxy a' a b' b (W.WriterT w m) r writerP p = do (r, w) <- unsafeHoist lift p lift $ W.tell w return r {-# INLINABLE writerP #-} -- | Run 'W.WriterT' in the base monad runWriterP :: (Monad m, Monoid w) => Proxy a' a b' b (W.WriterT w m) r -> Proxy a' a b' b m (r, w) runWriterP p = W.runWriterT $ distribute p {-# INLINABLE runWriterP #-} -- | Execute 'W.WriterT' in the base monad execWriterP :: (Monad m, Monoid w) => Proxy a' a b' b (W.WriterT w m) r -> Proxy a' a b' b m w execWriterP p = fmap snd $ runWriterP p {-# INLINABLE execWriterP #-} -- | Wrap the base monad in 'RWS.RWST' rwsP :: (Monad m, Monoid w) => (i -> s -> Proxy a' a b' b m (r, s, w)) -> Proxy a' a b' b (RWS.RWST i w s m) r rwsP k = do i <- lift RWS.ask s <- lift RWS.get (r, s', w) <- unsafeHoist lift (k i s) lift $ do RWS.put s' RWS.tell w return r {-# INLINABLE rwsP #-} -- | Run 'RWS.RWST' in the base monad runRWSP :: (Monad m, Monoid w) => r -> s -> Proxy a' a b' b (RWS.RWST r w s m) d -> Proxy a' a b' b m (d, s, w) runRWSP i s p = (\b -> RWS.runRWST b i s) $ distribute p {-# INLINABLE runRWSP #-} -- | Evaluate 'RWS.RWST' in the base monad evalRWSP :: (Monad m, Monoid w) => r -> s -> Proxy a' a b' b (RWS.RWST r w s m) d -> Proxy a' a b' b m (d, w) evalRWSP i s p = fmap f $ runRWSP i s p where f x = let (r, _, w) = x in (r, w) {-# INLINABLE evalRWSP #-} -- | Execute 'RWS.RWST' in the base monad execRWSP :: (Monad m, Monoid w) => r -> s -> Proxy a' a b' b (RWS.RWST r w s m) d -> Proxy a' a b' b m (s, w) execRWSP i s p = fmap f $ runRWSP i s p where f x = let (_, s', w) = x in (s', w) {-# INLINABLE execRWSP #-} {- $tutorial Probably the most useful functionality in this module is lifted error handling. Suppose that you have a 'Pipes.Pipe' whose base monad can fail using 'E.ErrorT': > import Control.Monad.Trans.Error > import Pipes > > example :: Monad m => Pipe Int Int (ErrorT String m) r > example = for cat $ \n -> > if n == 0 > then lift $ throwError "Zero is forbidden" > else yield n Without the tools in this module you cannot recover from any potential error until after you compose and run the pipeline: >>> import qualified Pipes.Prelude as P >>> runErrorT $ runEffect $ P.readLn >-> example >-> P.print 42 42 1 1 0 Zero is forbidden >>> This module provides `catchError`, which lets you catch and recover from errors inside the 'Pipe': > import qualified Pipes.Lift as Lift > > caught :: Pipe Int Int (ErrorT String IO) r > caught = example `Lift.catchError` \str -> do > liftIO (putStrLn str) > caught This lets you resume streaming in the face of errors raised within the base monad: >>> runErrorT $ runEffect $ P.readLn >-> caught >-> P.print 0 Zero is forbidden 42 42 0 Zero is forbidden 1 1 ... Another common use case is running a base monad before running the pipeline. For example, the following contrived 'Producer' uses 'S.StateT' gratuitously to increment numbers: > import Control.Monad (forever) > import Control.Monad.Trans.State.Strict > import Pipes > > numbers :: Monad m => Producer Int (StateT Int m) r > numbers = forever $ do > n <- lift get > yield n > lift $ put $! n + 1 You can run the 'StateT' monad by supplying an initial state, before you ever compose the 'Producer': > import Pipes.Lift > > naturals :: Monad m => Producer Int m r > naturals = evalStateP 0 numbers This deletes 'StateT' from the base monad entirely, give you a completely pure 'Pipes.Producer': >>> Pipes.Prelude.toList naturals [0,1,2,3,4,5,6...] Note that the convention for the 'S.StateT' run functions is backwards from @transformers@ for convenience: the initial state is the first argument. All of these functions internally use 'distribute', which can pull out most monad transformers from the base monad. For example, 'evalStateP' is defined in terms of 'distribute': > evalStateP s p = evalStateT (distribute p) s Therefore you can use 'distribute' to run other monad transformers, too, as long as they implement the 'MFunctor' type class from the @mmorph@ library. -} pipes-4.1.9/src/Pipes/Prelude.hs0000644000000000000000000005523312713420457014653 0ustar0000000000000000{-| General purpose utilities The names in this module clash heavily with the Haskell Prelude, so I recommend the following import scheme: > import Pipes > import qualified Pipes.Prelude as P -- or use any other qualifier you prefer Note that 'String'-based 'IO' is inefficient. The 'String'-based utilities in this module exist only for simple demonstrations without incurring a dependency on the @text@ package. Also, 'stdinLn' and 'stdoutLn' remove and add newlines, respectively. This behavior is intended to simplify examples. The corresponding @stdin@ and @stdout@ utilities from @pipes-bytestring@ and @pipes-text@ preserve newlines. -} {-# LANGUAGE RankNTypes, Trustworthy #-} {-# OPTIONS_GHC -fno-warn-unused-do-bind #-} module Pipes.Prelude ( -- * Producers -- $producers stdinLn , readLn , fromHandle , repeatM , replicateM , unfoldr -- * Consumers -- $consumers , stdoutLn , stdoutLn' , mapM_ , print , toHandle , drain -- * Pipes -- $pipes , map , mapM , sequence , mapFoldable , filter , filterM , take , takeWhile , takeWhile' , drop , dropWhile , concat , elemIndices , findIndices , scan , scanM , chain , read , show , seq -- *ListT , loop -- * Folds -- $folds , fold , fold' , foldM , foldM' , all , any , and , or , elem , notElem , find , findIndex , head , index , last , length , maximum , minimum , null , sum , product , toList , toListM , toListM' -- * Zips , zip , zipWith -- * Utilities , tee , generalize ) where import Control.Exception (throwIO, try) import Control.Monad (liftM, when, unless) import Control.Monad.Trans.State.Strict (get, put) import Data.Functor.Identity (Identity, runIdentity) import Foreign.C.Error (Errno(Errno), ePIPE) import Pipes import Pipes.Core import Pipes.Internal import Pipes.Lift (evalStateP) import qualified GHC.IO.Exception as G import qualified System.IO as IO import qualified Prelude import Prelude hiding ( all , and , any , concat , drop , dropWhile , elem , filter , head , last , length , map , mapM , mapM_ , maximum , minimum , notElem , null , or , print , product , read , readLn , sequence , show , seq , sum , take , takeWhile , zip , zipWith ) {- $producers Use 'for' loops to iterate over 'Producer's whenever you want to perform the same action for every element: > -- Echo all lines from standard input to standard output > runEffect $ for P.stdinLn $ \str -> do > lift $ putStrLn str ... or more concisely: >>> runEffect $ for P.stdinLn (lift . putStrLn) Test Test ABC ABC ... -} {-| Read 'String's from 'IO.stdin' using 'getLine' Terminates on end of input -} stdinLn :: MonadIO m => Producer' String m () stdinLn = fromHandle IO.stdin {-# INLINABLE stdinLn #-} -- | 'read' values from 'IO.stdin', ignoring failed parses readLn :: (MonadIO m, Read a) => Producer' a m () readLn = stdinLn >-> read {-# INLINABLE readLn #-} {-| Read 'String's from a 'IO.Handle' using 'IO.hGetLine' Terminates on end of input -} fromHandle :: MonadIO m => IO.Handle -> Producer' String m () fromHandle h = go where go = do eof <- liftIO $ IO.hIsEOF h unless eof $ do str <- liftIO $ IO.hGetLine h yield str go {-# INLINABLE fromHandle #-} -- | Repeat a monadic action indefinitely, 'yield'ing each result repeatM :: Monad m => m a -> Producer' a m r repeatM m = lift m >~ cat {-# INLINABLE [1] repeatM #-} {-# RULES "repeatM m >-> p" forall m p . repeatM m >-> p = lift m >~ p #-} {-| Repeat a monadic action a fixed number of times, 'yield'ing each result > replicateM 0 x = return () > > replicateM (m + n) x = replicateM m x >> replicateM n x -- 0 <= {m,n} -} replicateM :: Monad m => Int -> m a -> Producer' a m () replicateM n m = lift m >~ take n {-# INLINABLE replicateM #-} {- $consumers Feed a 'Consumer' the same value repeatedly using ('>~'): >>> runEffect $ lift getLine >~ P.stdoutLn Test Test ABC ABC ... -} {-| Write 'String's to 'IO.stdout' using 'putStrLn' Unlike 'toHandle', 'stdoutLn' gracefully terminates on a broken output pipe -} stdoutLn :: MonadIO m => Consumer' String m () stdoutLn = go where go = do str <- await x <- liftIO $ try (putStrLn str) case x of Left (G.IOError { G.ioe_type = G.ResourceVanished , G.ioe_errno = Just ioe }) | Errno ioe == ePIPE -> return () Left e -> liftIO (throwIO e) Right () -> go {-# INLINABLE stdoutLn #-} {-| Write 'String's to 'IO.stdout' using 'putStrLn' This does not handle a broken output pipe, but has a polymorphic return value -} stdoutLn' :: MonadIO m => Consumer' String m r stdoutLn' = for cat (\str -> liftIO (putStrLn str)) {-# INLINABLE [1] stdoutLn' #-} {-# RULES "p >-> stdoutLn'" forall p . p >-> stdoutLn' = for p (\str -> liftIO (putStrLn str)) #-} -- | Consume all values using a monadic function mapM_ :: Monad m => (a -> m ()) -> Consumer' a m r mapM_ f = for cat (\a -> lift (f a)) {-# INLINABLE [1] mapM_ #-} {-# RULES "p >-> mapM_ f" forall p f . p >-> mapM_ f = for p (\a -> lift (f a)) #-} -- | 'print' values to 'IO.stdout' print :: (MonadIO m, Show a) => Consumer' a m r print = for cat (\a -> liftIO (Prelude.print a)) {-# INLINABLE [1] print #-} {-# RULES "p >-> print" forall p . p >-> print = for p (\a -> liftIO (Prelude.print a)) #-} -- | Write 'String's to a 'IO.Handle' using 'IO.hPutStrLn' toHandle :: MonadIO m => IO.Handle -> Consumer' String m r toHandle handle = for cat (\str -> liftIO (IO.hPutStrLn handle str)) {-# INLINABLE [1] toHandle #-} {-# RULES "p >-> toHandle handle" forall p handle . p >-> toHandle handle = for p (\str -> liftIO (IO.hPutStrLn handle str)) #-} -- | 'discard' all incoming values drain :: Monad m => Consumer' a m r drain = for cat discard {-# INLINABLE [1] drain #-} {-# RULES "p >-> drain" forall p . p >-> drain = for p discard #-} {- $pipes Use ('>->') to connect 'Producer's, 'Pipe's, and 'Consumer's: >>> runEffect $ P.stdinLn >-> P.takeWhile (/= "quit") >-> P.stdoutLn Test Test ABC ABC quit >>> -} {-| Apply a function to all values flowing downstream > map id = cat > > map (g . f) = map f >-> map g -} map :: Monad m => (a -> b) -> Pipe a b m r map f = for cat (\a -> yield (f a)) {-# INLINABLE [1] map #-} {-# RULES "p >-> map f" forall p f . p >-> map f = for p (\a -> yield (f a)) ; "map f >-> p" forall p f . map f >-> p = (do a <- await return (f a) ) >~ p #-} {-| Apply a monadic function to all values flowing downstream > mapM return = cat > > mapM (f >=> g) = mapM f >-> mapM g -} mapM :: Monad m => (a -> m b) -> Pipe a b m r mapM f = for cat $ \a -> do b <- lift (f a) yield b {-# INLINABLE [1] mapM #-} {-# RULES "p >-> mapM f" forall p f . p >-> mapM f = for p (\a -> do b <- lift (f a) yield b ) ; "mapM f >-> p" forall p f . mapM f >-> p = (do a <- await b <- lift (f a) return b ) >~ p #-} -- | Convert a stream of actions to a stream of values sequence :: Monad m => Pipe (m a) a m r sequence = mapM id {-# INLINABLE sequence #-} {- | Apply a function to all values flowing downstream, and forward each element of the result. -} mapFoldable :: (Monad m, Foldable t) => (a -> t b) -> Pipe a b m r mapFoldable f = for cat (\a -> each (f a)) {-# INLINABLE [1] mapFoldable #-} {-# RULES "p >-> mapFoldable f" forall p f . p >-> mapFoldable f = for p (\a -> each (f a)) #-} {-| @(filter predicate)@ only forwards values that satisfy the predicate. > filter (pure True) = cat > > filter (liftA2 (&&) p1 p2) = filter p1 >-> filter p2 -} filter :: Monad m => (a -> Bool) -> Pipe a a m r filter predicate = for cat $ \a -> when (predicate a) (yield a) {-# INLINABLE [1] filter #-} {-# RULES "p >-> filter predicate" forall p predicate. p >-> filter predicate = for p (\a -> when (predicate a) (yield a)) #-} {-| @(filterM predicate)@ only forwards values that satisfy the monadic predicate > filterM (pure (pure True)) = cat > > filterM (liftA2 (liftA2 (&&)) p1 p2) = filterM p1 >-> filterM p2 -} filterM :: Monad m => (a -> m Bool) -> Pipe a a m r filterM predicate = for cat $ \a -> do b <- lift (predicate a) when b (yield a) {-# INLINABLE [1] filterM #-} {-# RULES "p >-> filterM predicate" forall p predicate . p >-> filterM predicate = for p (\a -> do b <- lift (predicate a) when b (yield a) ) #-} {-| @(take n)@ only allows @n@ values to pass through > take 0 = return () > > take (m + n) = take m >> take n > take = cat > > take (min m n) = take m >-> take n -} take :: Monad m => Int -> Pipe a a m () take = loop where loop 0 = return () loop n = do a <- await yield a loop (n-1) {-# INLINABLE take #-} {-| @(takeWhile p)@ allows values to pass downstream so long as they satisfy the predicate @p@. > takeWhile (pure True) = cat > > takeWhile (liftA2 (&&) p1 p2) = takeWhile p1 >-> takeWhile p2 -} takeWhile :: Monad m => (a -> Bool) -> Pipe a a m () takeWhile predicate = go where go = do a <- await if (predicate a) then do yield a go else return () {-# INLINABLE takeWhile #-} {-| @(takeWhile' p)@ is a version of takeWhile that returns the value failing the predicate. > takeWhile' (pure True) = cat > > takeWhile' (liftA2 (&&) p1 p2) = takeWhile' p1 >-> takeWhile' p2 -} takeWhile' :: Monad m => (a -> Bool) -> Pipe a a m a takeWhile' predicate = go where go = do a <- await if (predicate a) then do yield a go else return a {-# INLINABLE takeWhile' #-} {-| @(drop n)@ discards @n@ values going downstream > drop 0 = cat > > drop (m + n) = drop m >-> drop n -} drop :: Monad m => Int -> Pipe a a m r drop = loop where loop 0 = cat loop n = do await loop (n-1) {-# INLINABLE drop #-} {-| @(dropWhile p)@ discards values going downstream until one violates the predicate @p@. > dropWhile (pure False) = cat > > dropWhile (liftA2 (||) p1 p2) = dropWhile p1 >-> dropWhile p2 -} dropWhile :: Monad m => (a -> Bool) -> Pipe a a m r dropWhile predicate = go where go = do a <- await if (predicate a) then go else do yield a cat {-# INLINABLE dropWhile #-} -- | Flatten all 'Foldable' elements flowing downstream concat :: (Monad m, Foldable f) => Pipe (f a) a m r concat = for cat each {-# INLINABLE [1] concat #-} {-# RULES "p >-> concat" forall p . p >-> concat = for p each #-} -- | Outputs the indices of all elements that match the given element elemIndices :: (Monad m, Eq a) => a -> Pipe a Int m r elemIndices a = findIndices (a ==) {-# INLINABLE elemIndices #-} -- | Outputs the indices of all elements that satisfied the predicate findIndices :: Monad m => (a -> Bool) -> Pipe a Int m r findIndices predicate = go 0 where go n = do a <- await when (predicate a) (yield n) go $! n + 1 {-# INLINABLE findIndices #-} {-| Strict left scan > Control.Foldl.purely scan :: Monad m => Fold a b -> Pipe a b m r -} scan :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Pipe a b m r scan step begin done = go begin where go x = do yield (done x) a <- await let x' = step x a go $! x' {-# INLINABLE scan #-} {-| Strict, monadic left scan > Control.Foldl.impurely scan :: Monad m => FoldM a m b -> Pipe a b m r -} scanM :: Monad m => (x -> a -> m x) -> m x -> (x -> m b) -> Pipe a b m r scanM step begin done = do x <- lift begin go x where go x = do b <- lift (done x) yield b a <- await x' <- lift (step x a) go $! x' {-# INLINABLE scanM #-} {-| Apply an action to all values flowing downstream > chain (pure (return ())) = cat > > chain (liftA2 (>>) m1 m2) = chain m1 >-> chain m2 -} chain :: Monad m => (a -> m ()) -> Pipe a a m r chain f = for cat $ \a -> do lift (f a) yield a {-# INLINABLE [1] chain #-} {-# RULES "p >-> chain f" forall p f . p >-> chain f = for p (\a -> do lift (f a) yield a ) ; "chain f >-> p" forall p f . chain f >-> p = (do a <- await lift (f a) return a ) >~ p #-} -- | Parse 'Read'able values, only forwarding the value if the parse succeeds read :: (Monad m, Read a) => Pipe String a m r read = for cat $ \str -> case (reads str) of [(a, "")] -> yield a _ -> return () {-# INLINABLE [1] read #-} {-# RULES "p >-> read" forall p . p >-> read = for p (\str -> case (reads str) of [(a, "")] -> yield a _ -> return () ) #-} -- | Convert 'Show'able values to 'String's show :: (Monad m, Show a) => Pipe a String m r show = map Prelude.show {-# INLINABLE show #-} -- | Evaluate all values flowing downstream to WHNF seq :: Monad m => Pipe a a m r seq = for cat $ \a -> yield $! a {-# INLINABLE seq #-} {-| Create a `Pipe` from a `ListT` transformation > loop (k1 >=> k2) = loop k1 >-> loop k2 > > loop return = cat -} loop :: Monad m => (a -> ListT m b) -> Pipe a b m r loop k = for cat (every . k) {-# INLINABLE loop #-} {- $folds Use these to fold the output of a 'Producer'. Many of these folds will stop drawing elements if they can compute their result early, like 'any': >>> P.any null P.stdinLn Test ABC True >>> -} {-| Strict fold of the elements of a 'Producer' > Control.Foldl.purely fold :: Monad m => Fold a b -> Producer a m () -> m b -} fold :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Producer a m () -> m b fold step begin done p0 = go p0 begin where go p x = case p of Request v _ -> closed v Respond a fu -> go (fu ()) $! step x a M m -> m >>= \p' -> go p' x Pure _ -> return (done x) {-# INLINABLE fold #-} {-| Strict fold of the elements of a 'Producer' that preserves the return value > Control.Foldl.purely fold' :: Monad m => Fold a b -> Producer a m r -> m (b, r) -} fold' :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Producer a m r -> m (b, r) fold' step begin done p0 = go p0 begin where go p x = case p of Request v _ -> closed v Respond a fu -> go (fu ()) $! step x a M m -> m >>= \p' -> go p' x Pure r -> return (done x, r) {-# INLINABLE fold' #-} {-| Strict, monadic fold of the elements of a 'Producer' > Control.Foldl.impurely foldM :: Monad m => FoldM a b -> Producer a m () -> m b -} foldM :: Monad m => (x -> a -> m x) -> m x -> (x -> m b) -> Producer a m () -> m b foldM step begin done p0 = do x0 <- begin go p0 x0 where go p x = case p of Request v _ -> closed v Respond a fu -> do x' <- step x a go (fu ()) $! x' M m -> m >>= \p' -> go p' x Pure _ -> done x {-# INLINABLE foldM #-} {-| Strict, monadic fold of the elements of a 'Producer' > Control.Foldl.impurely foldM' :: Monad m => FoldM a b -> Producer a m r -> m (b, r) -} foldM' :: Monad m => (x -> a -> m x) -> m x -> (x -> m b) -> Producer a m r -> m (b, r) foldM' step begin done p0 = do x0 <- begin go p0 x0 where go p x = case p of Request v _ -> closed v Respond a fu -> do x' <- step x a go (fu ()) $! x' M m -> m >>= \p' -> go p' x Pure r -> do b <- done x return (b, r) {-# INLINABLE foldM' #-} {-| @(all predicate p)@ determines whether all the elements of @p@ satisfy the predicate. -} all :: Monad m => (a -> Bool) -> Producer a m () -> m Bool all predicate p = null $ p >-> filter (\a -> not (predicate a)) {-# INLINABLE all #-} {-| @(any predicate p)@ determines whether any element of @p@ satisfies the predicate. -} any :: Monad m => (a -> Bool) -> Producer a m () -> m Bool any predicate p = liftM not $ null (p >-> filter predicate) {-# INLINABLE any #-} -- | Determines whether all elements are 'True' and :: Monad m => Producer Bool m () -> m Bool and = all id {-# INLINABLE and #-} -- | Determines whether any element is 'True' or :: Monad m => Producer Bool m () -> m Bool or = any id {-# INLINABLE or #-} {-| @(elem a p)@ returns 'True' if @p@ has an element equal to @a@, 'False' otherwise -} elem :: (Monad m, Eq a) => a -> Producer a m () -> m Bool elem a = any (a ==) {-# INLINABLE elem #-} {-| @(notElem a)@ returns 'False' if @p@ has an element equal to @a@, 'True' otherwise -} notElem :: (Monad m, Eq a) => a -> Producer a m () -> m Bool notElem a = all (a /=) {-# INLINABLE notElem #-} -- | Find the first element of a 'Producer' that satisfies the predicate find :: Monad m => (a -> Bool) -> Producer a m () -> m (Maybe a) find predicate p = head (p >-> filter predicate) {-# INLINABLE find #-} {-| Find the index of the first element of a 'Producer' that satisfies the predicate -} findIndex :: Monad m => (a -> Bool) -> Producer a m () -> m (Maybe Int) findIndex predicate p = head (p >-> findIndices predicate) {-# INLINABLE findIndex #-} -- | Retrieve the first element from a 'Producer' head :: Monad m => Producer a m () -> m (Maybe a) head p = do x <- next p return $ case x of Left _ -> Nothing Right (a, _) -> Just a {-# INLINABLE head #-} -- | Index into a 'Producer' index :: Monad m => Int -> Producer a m () -> m (Maybe a) index n p = head (p >-> drop n) {-# INLINABLE index #-} -- | Retrieve the last element from a 'Producer' last :: Monad m => Producer a m () -> m (Maybe a) last p0 = do x <- next p0 case x of Left _ -> return Nothing Right (a, p') -> go a p' where go a p = do x <- next p case x of Left _ -> return (Just a) Right (a', p') -> go a' p' {-# INLINABLE last #-} -- | Count the number of elements in a 'Producer' length :: Monad m => Producer a m () -> m Int length = fold (\n _ -> n + 1) 0 id {-# INLINABLE length #-} -- | Find the maximum element of a 'Producer' maximum :: (Monad m, Ord a) => Producer a m () -> m (Maybe a) maximum = fold step Nothing id where step x a = Just $ case x of Nothing -> a Just a' -> max a a' {-# INLINABLE maximum #-} -- | Find the minimum element of a 'Producer' minimum :: (Monad m, Ord a) => Producer a m () -> m (Maybe a) minimum = fold step Nothing id where step x a = Just $ case x of Nothing -> a Just a' -> min a a' {-# INLINABLE minimum #-} -- | Determine if a 'Producer' is empty null :: Monad m => Producer a m () -> m Bool null p = do x <- next p return $ case x of Left _ -> True Right _ -> False {-# INLINABLE null #-} -- | Compute the sum of the elements of a 'Producer' sum :: (Monad m, Num a) => Producer a m () -> m a sum = fold (+) 0 id {-# INLINABLE sum #-} -- | Compute the product of the elements of a 'Producer' product :: (Monad m, Num a) => Producer a m () -> m a product = fold (*) 1 id {-# INLINABLE product #-} -- | Convert a pure 'Producer' into a list toList :: Producer a Identity () -> [a] toList = go where go p = case p of Request v _ -> closed v Respond a fu -> a:go (fu ()) M m -> go (runIdentity m) Pure _ -> [] {-# INLINABLE toList #-} {-| Convert an effectful 'Producer' into a list Note: 'toListM' is not an idiomatic use of @pipes@, but I provide it for simple testing purposes. Idiomatic @pipes@ style consumes the elements immediately as they are generated instead of loading all elements into memory. -} toListM :: Monad m => Producer a m () -> m [a] toListM = fold step begin done where step x a = x . (a:) begin = id done x = x [] {-# INLINABLE toListM #-} {-| Convert an effectful 'Producer' into a list alongside the return value Note: 'toListM'' is not an idiomatic use of @pipes@, but I provide it for simple testing purposes. Idiomatic @pipes@ style consumes the elements immediately as they are generated instead of loading all elements into memory. -} toListM' :: Monad m => Producer a m r -> m ([a], r) toListM' = fold' step begin done where step x a = x . (a:) begin = id done x = x [] {-# INLINABLE toListM' #-} -- | Zip two 'Producer's zip :: Monad m => (Producer a m r) -> (Producer b m r) -> (Producer' (a, b) m r) zip = zipWith (,) {-# INLINABLE zip #-} -- | Zip two 'Producer's using the provided combining function zipWith :: Monad m => (a -> b -> c) -> (Producer a m r) -> (Producer b m r) -> (Producer' c m r) zipWith f = go where go p1 p2 = do e1 <- lift $ next p1 case e1 of Left r -> return r Right (a, p1') -> do e2 <- lift $ next p2 case e2 of Left r -> return r Right (b, p2') -> do yield (f a b) go p1' p2' {-# INLINABLE zipWith #-} {-| Transform a 'Consumer' to a 'Pipe' that reforwards all values further downstream -} tee :: Monad m => Consumer a m r -> Pipe a a m r tee p = evalStateP Nothing $ do r <- up >\\ (hoist lift p //> dn) ma <- lift get case ma of Nothing -> return () Just a -> yield a return r where up () = do ma <- lift get case ma of Nothing -> return () Just a -> yield a a <- await lift $ put (Just a) return a dn v = closed v {-# INLINABLE tee #-} {-| Transform a unidirectional 'Pipe' to a bidirectional 'Proxy' > generalize (f >-> g) = generalize f >+> generalize g > > generalize cat = pull -} generalize :: Monad m => Pipe a b m r -> x -> Proxy x a x b m r generalize p x0 = evalStateP x0 $ up >\\ hoist lift p //> dn where up () = do x <- lift get request x dn a = do x <- respond a lift $ put x {-# INLINABLE generalize #-} {-| The natural unfold into a 'Producer' with a step function and a seed > unfoldr next = id -} unfoldr :: Monad m => (s -> m (Either r (a, s))) -> s -> Producer a m r unfoldr step = go where go s0 = do e <- lift (step s0) case e of Left r -> return r Right (a,s) -> do yield a go s {-# INLINABLE unfoldr #-} pipes-4.1.9/src/Pipes/Tutorial.hs0000644000000000000000000014421512707257672015067 0ustar0000000000000000{-# OPTIONS_GHC -fno-warn-unused-imports #-} {-| Conventional Haskell stream programming forces you to choose only two of the following three features: * Effects * Streaming * Composability If you sacrifice /Effects/ you get Haskell's pure and lazy lists, which you can transform using composable functions in constant space, but without interleaving effects. If you sacrifice /Streaming/ you get 'mapM', 'forM' and \"ListT done wrong\", which are composable and effectful, but do not return a single result until the whole list has first been processed and loaded into memory. If you sacrifice /Composability/ you write a tightly coupled read, transform, and write loop in 'IO', which is streaming and effectful, but is not modular or separable. @pipes@ gives you all three features: effectful, streaming, and composable programming. @pipes@ also provides a wide variety of stream programming abstractions which are all subsets of a single unified machinery: * effectful 'Producer's (like generators), * effectful 'Consumer's (like iteratees), * effectful 'Pipe's (like Unix pipes), and: * 'ListT' done right. All of these are connectable and you can combine them together in clever and unexpected ways because they all share the same underlying type. @pipes@ requires a basic understanding of monad transformers, which you can learn about by reading either: * the paper \"Monad Transformers - Step by Step\", * part III \"Monads in the Real World\" of the tutorial \"All About Monads\", * chapter 18 of \"Real World Haskell\" on monad transformers, or: * the documentation of the @transformers@ library. If you want a Quick Start guide to @pipes@, read the documentation in "Pipes.Prelude" from top to bottom. This tutorial is more extensive and explains the @pipes@ API in greater detail and illustrates several idioms. -} module Pipes.Tutorial ( -- * Introduction -- $introduction -- * Producers -- $producers -- * Composability -- $composability -- * Consumers -- $consumers -- * Pipes -- $pipes -- * ListT -- $listT -- * Tricks -- $tricks -- * Conclusion -- $conclusion -- * Appendix: Types -- $types -- * Appendix: Time Complexity -- $timecomplexity -- * Copyright -- $copyright ) where import Control.Category import Control.Monad import Control.Monad.Trans.Error import Control.Monad.Trans.Writer.Strict import Pipes import Pipes.Lift import qualified Pipes.Prelude as P import Prelude hiding ((.), id) {- $introduction The @pipes@ library decouples stream processing stages from each other so that you can mix and match diverse stages to produce useful streaming programs. If you are a library writer, @pipes@ lets you package up streaming components into a reusable interface. If you are an application writer, @pipes@ lets you connect pre-made streaming components with minimal effort to produce a highly-efficient program that streams data in constant memory. To enforce loose coupling, components can only communicate using two commands: * 'yield': Send output data * 'await': Receive input data @pipes@ has four types of components built around these two commands: * 'Producer's can only 'yield' values and they model streaming sources * 'Consumer's can only 'await' values and they model streaming sinks * 'Pipe's can both 'yield' and 'await' values and they model stream transformations * 'Effect's can neither 'yield' nor 'await' and they model non-streaming components You can connect these components together in four separate ways which parallel the four above types: * 'for' handles 'yield's * ('>~') handles 'await's * ('>->') handles both 'yield's and 'await's * ('>>=') handles return values As you connect components their types will change to reflect inputs and outputs that you've fused away. You know that you're done connecting things when you get an 'Effect', meaning that you have handled all inputs and outputs. You run this final 'Effect' to begin streaming. -} {- $producers 'Producer's are effectful streams of input. Specifically, a 'Producer' is a monad transformer that extends any base monad with a new 'yield' command. This 'yield' command lets you send output downstream to an anonymous handler, decoupling how you generate values from how you consume them. The following @stdinLn@ 'Producer' shows how to incrementally read in 'String's from standard input and 'yield' them downstream, terminating gracefully when reaching the end of the input: > -- echo.hs > > import Control.Monad (unless) > import Pipes > import System.IO (isEOF) > > -- +--------+-- A 'Producer' that yields 'String's > -- | | > -- | | +-- Every monad transformer has a base monad. > -- | | | This time the base monad is 'IO'. > -- | | | > -- | | | +-- Every monadic action has a return value. > -- | | | | This action returns '()' when finished > -- v v v v > stdinLn :: Producer String IO () > stdinLn = do > eof <- lift isEOF -- 'lift' an 'IO' action from the base monad > unless eof $ do > str <- lift getLine > yield str -- 'yield' the 'String' > stdinLn -- Loop 'yield' emits a value, suspending the current 'Producer' until the value is consumed. If nobody consumes the value (which is possible) then 'yield' never returns. You can think of 'yield' as having the following type: @ 'yield' :: 'Monad' m => a -> 'Producer' a m () @ The true type of 'yield' is actually more general and powerful. Throughout the tutorial I will present type signatures like this that are simplified at first and then later reveal more general versions. So read the above type signature as simply saying: \"You can use 'yield' within a 'Producer', but you may be able to use 'yield' in other contexts, too.\" Click the link to 'yield' to navigate to its documentation. There you will see that 'yield' actually uses the 'Producer'' (with an apostrophe) type synonym which hides a lot of polymorphism behind a simple veneer. The documentation for 'yield' says that you can also use 'yield' within a 'Pipe', too, because of this polymorphism: @ 'yield' :: 'Monad' m => a -> 'Pipe' x a m () @ Use simpler types like these to guide you until you understand the fully general type. 'for' loops are the simplest way to consume a 'Producer' like @stdinLn@. 'for' has the following type: @ \-\- +-- Producer +-- The body of the +-- Result \-\- | to loop | loop | \-\- v over v v \-\- -------------- ------------------ ---------- 'for' :: 'Monad' m => 'Producer' a m r -> (a -> 'Effect' m ()) -> 'Effect' m r @ @(for producer body)@ loops over @(producer)@, substituting each 'yield' in @(producer)@ with @(body)@. You can also deduce that behavior purely from the type signature: * The body of the loop takes exactly one argument of type @(a)@, which is the same as the output type of the 'Producer'. Therefore, the body of the loop must get its input from that 'Producer' and nowhere else. * The return value of the input 'Producer' matches the return value of the result, therefore 'for' must loop over the entire 'Producer' and not skip anything. The above type signature is not the true type of 'for', which is actually more general. Think of the above type signature as saying: \"If the first argument of 'for' is a 'Producer' and the second argument returns an 'Effect', then the final result must be an 'Effect'.\" Click the link to 'for' to navigate to its documentation. There you will see the fully general type and underneath you will see equivalent simpler types. One of these says that if the body of the loop is a 'Producer', then the result is a 'Producer', too: @ 'for' :: 'Monad' m => 'Producer' a m r -> (a -> 'Producer' b m ()) -> 'Producer' b m r @ The first type signature I showed for 'for' was a special case of this slightly more general signature because a 'Producer' that never 'yield's is also an 'Effect': @ data 'X' -- The uninhabited type \ type 'Effect' m r = 'Producer' 'X' m r @ This is why 'for' permits two different type signatures. The first type signature is just a special case of the second one: @ 'for' :: 'Monad' m => 'Producer' a m r -> (a -> 'Producer' b m ()) -> 'Producer' b m r \ -- Specialize \'b\' to \'X\' 'for' :: 'Monad' m => 'Producer' a m r -> (a -> 'Producer' 'X' m ()) -> 'Producer' 'X' m r \ -- Producer X = Effect 'for' :: 'Monad' m => 'Producer' a m r -> (a -> 'Effect' m ()) -> 'Effect' m r @ This is the same trick that all @pipes@ functions use to work with various combinations of 'Producer's, 'Consumer's, 'Pipe's, and 'Effect's. Each function really has just one general type, which you can then simplify down to multiple useful alternative types. Here's an example use of a 'for' @loop@, where the second argument (the loop body) is an 'Effect': > -- echo.hs > > loop :: Effect IO () > loop = for stdinLn $ \str -> do -- Read this like: "for str in stdinLn" > lift $ putStrLn str -- The body of the 'for' loop > > -- more concise: loop = for stdinLn (lift . putStrLn) In this example, 'for' loops over @stdinLn@ and replaces every 'yield' in @stdinLn@ with the body of the loop, printing each line. This is exactly equivalent to the following code, which I've placed side-by-side with the original definition of @stdinLn@ for comparison: > loop = do | stdinLn = do > eof <- lift isEOF | eof <- lift isEOF > unless eof $ do | unless eof $ do > str <- lift getLine | str <- lift getLine > (lift . putStrLn) str | yield str > loop | stdinLn You can think of 'yield' as creating a hole and a 'for' loop is one way to fill that hole. Notice how the final @loop@ only 'lift's actions from the base monad and does nothing else. This property is true for all 'Effect's, which are just glorified wrappers around actions in the base monad. This means we can run these 'Effect's to remove their 'lift's and lower them back to the equivalent computation in the base monad: @ 'runEffect' :: 'Monad' m => 'Effect' m r -> m r @ This is the real type signature of 'runEffect', which refuses to accept anything other than an 'Effect'. This ensures that we handle all inputs and outputs before streaming data: > -- echo.hs > > main :: IO () > main = runEffect loop ... or you could inline the entire @loop@ into the following one-liner: > main = runEffect $ for stdinLn (lift . putStrLn) Our final program loops over standard input and echoes every line to standard output until we hit @Ctrl-D@ to end the input stream: > $ ghc -O2 echo.hs > $ ./echo > Test > Test > ABC > ABC > > $ The final behavior is indistinguishable from just removing all the 'lift's from @loop@: > main = do | loop = do > eof <- isEof | eof <- lift isEof > unless eof $ do | unless eof $ do > str <- getLine | str <- lift getLine > putStrLn str | (lift . putStrLn) str > main | loop This @main@ is what we might have written by hand if we were not using @pipes@, but with @pipes@ we can decouple the input and output logic from each other. When we connect them back together, we still produce streaming code equivalent to what a sufficiently careful Haskell programmer would have written. You can also use 'for' to loop over lists, too. To do so, convert the list to a 'Producer' using 'each', which is exported by default from "Pipes": > each :: Monad m => [a] -> Producer a m () > each as = mapM_ yield as Combine 'for' and 'each' to iterate over lists using a \"foreach\" loop: >>> runEffect $ for (each [1..4]) (lift . print) 1 2 3 4 'each' is actually more general and works for any 'Foldable': @ 'each' :: ('Monad' m, 'Foldable' f) => f a -> 'Producer' a m () @ So you can loop over any 'Foldable' container or even a 'Maybe': >>> runEffect $ for (each (Just 1)) (lift . print) 1 -} {- $composability You might wonder why the body of a 'for' loop can be a 'Producer'. Let's test out this feature by defining a new loop body that creates three copies of every value: > -- nested.hs > > import Pipes > import qualified Pipes.Prelude as P -- Pipes.Prelude already has 'stdinLn' > > triple :: Monad m => a -> Producer a m () > triple x = do > yield x > yield x > yield x > > loop :: Producer String IO () > loop = for P.stdinLn triple > > -- This is the exact same as: > -- > -- loop = for P.stdinLn $ \x -> do > -- yield x > -- yield x > -- yield x This time our @loop@ is a 'Producer' that outputs 'String's, specifically three copies of each line that we read from standard input. Since @loop@ is a 'Producer' we cannot run it because there is still unhandled output. However, we can use yet another 'for' to handle this new repeated stream: > -- nested.hs > > main = runEffect $ for loop (lift . putStrLn) This creates a program which echoes every line from standard input to standard output three times: > $ ./nested > Test > Test > Test > Test > ABC > ABC > ABC > ABC > > $ But is this really necessary? Couldn't we have instead written this using a nested for loop? > main = runEffect $ > for P.stdinLn $ \str1 -> > for (triple str1) $ \str2 -> > lift $ putStrLn str2 Yes, we could have! In fact, this is a special case of the following equality, which always holds no matter what: @ \-\- s :: Monad m => 'Producer' a m () -- i.e. \'P.stdinLn\' \-\- f :: Monad m => a -> 'Producer' b m () -- i.e. \'triple\' \-\- g :: Monad m => b -> 'Producer' c m () -- i.e. \'(lift . putStrLn)\' \ for (for s f) g = for s (\\x -> for (f x) g) @ We can understand the rationale behind this equality if we first define the following operator that is the point-free counterpart to 'for': @ (~>) :: Monad m => (a -> 'Producer' b m ()) -> (b -> 'Producer' c m ()) -> (a -> 'Producer' c m ()) (f ~> g) x = for (f x) g @ Using ('~>') (pronounced \"into\"), we can transform our original equality into the following more symmetric equation: @ f :: Monad m => a -> 'Producer' b m () g :: Monad m => b -> 'Producer' c m () h :: Monad m => c -> 'Producer' d m () \ \-\- Associativity (f ~> g) ~> h = f ~> (g ~> h) @ This looks just like an associativity law. In fact, ('~>') has another nice property, which is that 'yield' is its left and right identity: > -- Left Identity > yield ~> f = f > -- Right Identity > f ~> yield = f In other words, 'yield' and ('~>') form a 'Category', specifically the generator category, where ('~>') plays the role of the composition operator and 'yield' is the identity. If you don't know what a 'Category' is, that's okay, and category theory is not a prerequisite for using @pipes@. All you really need to know is that @pipes@ uses some simple category theory to keep the API intuitive and easy to use. Notice that if we translate the left identity law to use 'for' instead of ('~>') we get: > for (yield x) f = f x This just says that if you iterate over a pure single-element 'Producer', then you could instead cut out the middle man and directly apply the body of the loop to that single element. If we translate the right identity law to use 'for' instead of ('~>') we get: > for s yield = s This just says that if the only thing you do is re-'yield' every element of a stream, you get back your original stream. These three \"for loop\" laws summarize our intuition for how 'for' loops should behave and because these are 'Category' laws in disguise that means that 'Producer's are composable in a rigorous sense of the word. In fact, we get more out of this than just a bunch of equations. We also get a useful operator: ('~>'). We can use this operator to condense our original code into the following more succinct form that composes two transformations: > main = runEffect $ for P.stdinLn (triple ~> lift . putStrLn) This means that we can also choose to program in a more functional style and think of stream processing in terms of composing transformations using ('~>') instead of nesting a bunch of 'for' loops. The above example is a microcosm of the design philosophy behind the @pipes@ library: * Define the API in terms of categories * Specify expected behavior in terms of category laws * Think compositionally instead of sequentially -} {- $consumers Sometimes you don't want to use a 'for' loop because you don't want to consume every element of a 'Producer' or because you don't want to process every value of a 'Producer' the exact same way. The most general solution is to externally iterate over the 'Producer' using the 'next' command: @ 'next' :: 'Monad' m => 'Producer' a m r -> m ('Either' r (a, 'Producer' a m r)) @ Think of 'next' as pattern matching on the head of the 'Producer'. This 'Either' returns a 'Left' if the 'Producer' is done or it returns a 'Right' containing the next value, @a@, along with the remainder of the 'Producer'. However, sometimes we can get away with something a little more simple and elegant, like a 'Consumer', which represents an effectful sink of values. A 'Consumer' is a monad transformer that extends the base monad with a new 'await' command. This 'await' command lets you receive input from an anonymous upstream source. The following @stdoutLn@ 'Consumer' shows how to incrementally 'await' 'String's and print them to standard output, terminating gracefully when receiving a broken pipe error: > import Control.Monad (unless) > import Control.Exception (try, throwIO) > import qualified GHC.IO.Exception as G > import Pipes > > -- +--------+-- A 'Consumer' that awaits 'String's > -- | | > -- v v > stdoutLn :: Consumer String IO () > stdoutLn = do > str <- await -- 'await' a 'String' > x <- lift $ try $ putStrLn str > case x of > -- Gracefully terminate if we got a broken pipe error > Left e@(G.IOError { G.ioe_type = t}) -> > lift $ unless (t == G.ResourceVanished) $ throwIO e > -- Otherwise loop > Right () -> stdoutLn 'await' is the dual of 'yield': we suspend our 'Consumer' until we receive a new value. If nobody provides a value (which is possible) then 'await' never returns. You can think of 'await' as having the following type: @ 'await' :: 'Monad' m => 'Consumer' a m a @ One way to feed a 'Consumer' is to repeatedly feed the same input using ('>~') (pronounced \"feed\"): @ \-\- +- Feed +- Consumer to +- Returns new \-\- | action | feed | Effect \-\- v v v \-\- ---------- -------------- ---------- ('>~') :: 'Monad' m => 'Effect' m b -> 'Consumer' b m c -> 'Effect' m c @ @(draw >~ consumer)@ loops over @(consumer)@, substituting each 'await' in @(consumer)@ with @(draw)@. So the following code replaces every 'await' in 'P.stdoutLn' with @(lift getLine)@ and then removes all the 'lift's: >>> runEffect $ lift getLine >~ stdoutLn Test Test ABC ABC 42 42 ... You might wonder why ('>~') uses an 'Effect' instead of a raw action in the base monad. The reason why is that ('>~') actually permits the following more general type: @ ('>~') :: 'Monad' m => 'Consumer' a m b -> 'Consumer' b m c -> 'Consumer' a m c @ ('>~') is the dual of ('~>'), composing 'Consumer's instead of 'Producer's. This means that you can feed a 'Consumer' with yet another 'Consumer' so that you can 'await' while you 'await'. For example, we could define the following intermediate 'Consumer' that requests two 'String's and returns them concatenated: > doubleUp :: Monad m => Consumer String m String > doubleUp = do > str1 <- await > str2 <- await > return (str1 ++ str2) > > -- more concise: doubleUp = (++) <$> await <*> await We can now insert this in between @(lift getLine)@ and @stdoutLn@ and see what happens: >>> runEffect $ lift getLine >~ doubleUp >~ stdoutLn Test ing Testing ABC DEF ABCDEF 42 000 42000 ... 'doubleUp' splits every request from 'stdoutLn' into two separate requests and returns back the concatenated result. We didn't need to parenthesize the above chain of ('>~') operators, because ('>~') is associative: > -- Associativity > (f >~ g) >~ h = f >~ (g >~ h) ... so we can always omit the parentheses since the meaning is unambiguous: > f >~ g >~ h Also, ('>~') has an identity, which is 'await'! > -- Left identity > await >~ f = f > > -- Right Identity > f >~ await = f In other words, ('>~') and 'await' form a 'Category', too, specifically the iteratee category, and 'Consumer's are also composable. -} {- $pipes Our previous programs were unsatisfactory because they were biased either towards the 'Producer' end or the 'Consumer' end. As a result, we had to choose between gracefully handling end of input (using 'P.stdinLn') or gracefully handling end of output (using 'P.stdoutLn'), but not both at the same time. However, we don't need to restrict ourselves to using 'Producer's exclusively or 'Consumer's exclusively. We can connect 'Producer's and 'Consumer's directly together using ('>->') (pronounced \"pipe\"): @ ('>->') :: 'Monad' m => 'Producer' a m r -> 'Consumer' a m r -> 'Effect' m r @ This returns an 'Effect' which we can run: > -- echo2.hs > > import Pipes > import qualified Pipes.Prelude as P -- Pipes.Prelude also provides 'stdoutLn' > > main = runEffect $ P.stdinLn >-> P.stdoutLn This program is more declarative of our intent: we want to stream values from 'P.stdinLn' to 'P.stdoutLn'. The above \"pipeline\" not only echoes standard input to standard output, but also handles both end of input and broken pipe errors: > $ ./echo2 > Test > Test > ABC > ABC > 42 > 42 > > $ ('>->') is \"pull-based\" meaning that control flow begins at the most downstream component (i.e. 'P.stdoutLn' in the above example). Any time a component 'await's a value it blocks and transfers control upstream and every time a component 'yield's a value it blocks and restores control back downstream, satisfying the 'await'. So in the above example, ('>->') matches every 'await' from 'P.stdoutLn' with a 'yield' from 'P.stdinLn'. Streaming stops when either 'P.stdinLn' terminates (i.e. end of input) or 'P.stdoutLn' terminates (i.e. broken pipe). This is why ('>->') requires that both the 'Producer' and 'Consumer' share the same type of return value: whichever one terminates first provides the return value for the entire 'Effect'. Let's test this by modifying our 'Producer' and 'Consumer' to each return a diagnostic 'String': > -- echo3.hs > > import Control.Applicative ((<$)) -- (<$) modifies return values > import Pipes > import qualified Pipes.Prelude as P > import System.IO > > main = do > hSetBuffering stdout NoBuffering > str <- runEffect $ > ("End of input!" <$ P.stdinLn) >-> ("Broken pipe!" <$ P.stdoutLn) > hPutStrLn stderr str This lets us diagnose whether the 'Producer' or 'Consumer' terminated first: > $ ./echo3 > Test > Test > > End of input! > $ ./echo3 | perl -e 'close STDIN' > Test > Broken pipe! > $ You might wonder why ('>->') returns an 'Effect' that we have to run instead of directly returning an action in the base monad. This is because you can connect things other than 'Producer's and 'Consumer's, like 'Pipe's, which are effectful stream transformations. A 'Pipe' is a monad transformer that is a mix between a 'Producer' and 'Consumer', because a 'Pipe' can both 'await' and 'yield'. The following example 'Pipe' is analagous to the Prelude's 'take', only allowing a fixed number of values to flow through: > -- take.hs > > import Control.Monad (replicateM_) > import Pipes > import Prelude hiding (take) > > -- +--------- A 'Pipe' that > -- | +---- 'await's 'a's and > -- | | +-- 'yield's 'a's > -- | | | > -- v v v > take :: Int -> Pipe a a IO () > take n = do > replicateM_ n $ do -- Repeat this block 'n' times > x <- await -- 'await' a value of type 'a' > yield x -- 'yield' a value of type 'a' > lift $ putStrLn "You shall not pass!" -- Fly, you fools! You can use 'Pipe's to transform 'Producer's, 'Consumer's, or even other 'Pipe's using the same ('>->') operator: @ ('>->') :: 'Monad' m => 'Producer' a m r -> 'Pipe' a b m r -> 'Producer' b m r ('>->') :: 'Monad' m => 'Pipe' a b m r -> 'Consumer' b m r -> 'Consumer' a m r ('>->') :: 'Monad' m => 'Pipe' a b m r -> 'Pipe' b c m r -> 'Pipe' a c m r @ For example, you can compose 'P.take' after 'P.stdinLn' to limit the number of lines drawn from standard input: > maxInput :: Int -> Producer String IO () > maxInput n = P.stdinLn >-> take n >>> runEffect $ maxInput 3 >-> P.stdoutLn Test Test ABC ABC 42 42 You shall not pass! >>> ... or you can pre-compose 'P.take' before 'P.stdoutLn' to limit the number of lines written to standard output: > maxOutput :: Int -> Consumer String IO () > maxOutput n = take n >-> P.stdoutLn >>> runEffect $ P.stdinLn >-> maxOutput 3 Those both gave the same behavior because ('>->') is associative: > (p1 >-> p2) >-> p3 = p1 >-> (p2 >-> p3) Therefore we can just leave out the parentheses: >>> runEffect $ P.stdinLn >-> take 3 >-> P.stdoutLn ('>->') is designed to behave like the Unix pipe operator, except with less quirks. In fact, we can continue the analogy to Unix by defining 'cat' (named after the Unix @cat@ utility), which reforwards elements endlessly: > cat :: Monad m => Pipe a a m r > cat = forever $ do > x <- await > yield x 'cat' is the identity of ('>->'), meaning that 'cat' satisfies the following two laws: > -- Useless use of 'cat' > cat >-> p = p > > -- Forwarding output to 'cat' does nothing > p >-> cat = p Therefore, ('>->') and 'cat' form a 'Category', specifically the category of Unix pipes, and 'Pipe's are also composable. A lot of Unix tools have very simple definitions when written using @pipes@: > -- unix.hs > > import Control.Monad (forever) > import Pipes > import qualified Pipes.Prelude as P -- Pipes.Prelude provides 'take', too > import Prelude hiding (head) > > head :: Monad m => Int -> Pipe a a m () > head = P.take > > yes :: Monad m => Producer String m r > yes = forever $ yield "y" > > main = runEffect $ yes >-> head 3 >-> P.stdoutLn This prints out 3 \'@y@\'s, just like the equivalent Unix pipeline: > $ ./unix > y > y > y > $ yes | head -3 > y > y > y > $ This lets us write \"Haskell pipes\" instead of Unix pipes. These are much easier to build than Unix pipes and we can connect them directly within Haskell for interoperability with the Haskell language and ecosystem. -} {- $listT @pipes@ also provides a \"ListT done right\" implementation. This differs from the implementation in @transformers@ because this 'ListT': * obeys the monad laws, and * streams data immediately instead of collecting all results into memory. The latter property is actually an elegant consequence of obeying the monad laws. To bind a list within a 'ListT' computation, combine 'Select' and 'each': > import Pipes > > pair :: ListT IO (Int, Int) > pair = do > x <- Select $ each [1, 2] > lift $ putStrLn $ "x = " ++ show x > y <- Select $ each [3, 4] > lift $ putStrLn $ "y = " ++ show y > return (x, y) You can then loop over a 'ListT' by using 'every': @ 'every' :: 'Monad' m => 'ListT' m a -> 'Producer' a m () @ So you can use your 'ListT' within a 'for' loop: >>> runEffect $ for (every pair) (lift . print) x = 1 y = 3 (1,3) y = 4 (1,4) x = 2 y = 3 (2,3) y = 4 (2,4) ... or a pipeline: >>> import qualified Pipes.Prelude as P >>> runEffect $ every pair >-> P.print Note that 'ListT' is lazy and only produces as many elements as we request: >>> runEffect $ for (every pair >-> P.take 2) (lift . print) x = 1 y = 3 (1,3) y = 4 (1,4) You can also go the other way, binding 'Producer's directly within a 'ListT'. In fact, this is actually what 'Select' was already doing: @ 'Select' :: 'Producer' a m () -> 'ListT' m a @ This lets you write crazy code like: > import Pipes > import qualified Pipes.Prelude as P > > input :: Producer String IO () > input = P.stdinLn >-> P.takeWhile (/= "quit") > > name :: ListT IO String > name = do > firstName <- Select input > lastName <- Select input > return (firstName ++ " " ++ lastName) Here we're binding standard input non-deterministically (twice) as if it were an effectful list: >>> runEffect $ every name >-> P.stdoutLn Daniel Fischer Daniel Fischer Wagner Daniel Wagner quit Donald Stewart Donald Stewart Duck Donald Duck quit quit >>> Notice how this streams out values immediately as they are generated, rather than building up a large intermediate result and then printing all the values in one batch at the end. `ListT` computations can be combined in more ways than `Pipe`s, so try to program in `ListT` as much as possible and defer converting it to a `Pipe` as late as possible using `P.loop`. You can combine `ListT` computations even if their inputs and outputs are completely different: > data In > = InA A > | InB B > | InC C > > data Out > = OutD D > | OutE E > | OutF F > > -- Independent computations > > example1 :: A -> ListT IO D > example2 :: B -> ListT IO E > example3 :: C -> ListT IO F > > -- Combined computation > > total :: In -> ListT IO Out > total input = case input of > InA a -> fmap OutD (example1 a) > InB b -> fmap OutE (example2 b) > InC c -> fmap OutF (example3 c) Sometimes you have multiple computations that handle different inputs but the same output, in which case you don't need to unify their outputs: > -- Overlapping outputs > > example1 :: A -> ListT IO Out > example2 :: B -> ListT IO Out > example3 :: C -> ListT IO Out > > -- Combined computation > > total :: In -> ListT IO Out > total input = case input of > InA a -> example1 a > InB b -> example2 b > InC c -> example3 c Other times you have multiple computations that handle the same input but produce different outputs. You can unify their outputs using the `Monoid` and `Functor` instances for `ListT`: > -- Overlapping inputs > > example1 :: In -> ListT IO D > example2 :: In -> ListT IO E > example3 :: In -> ListT IO F > > -- Combined computation > > total :: In -> ListT IO Out > total input = > fmap OutD (example1 input) > <> fmap OutE (example2 input) > <> fmap OutF (example3 input) You can also chain `ListT` computations, feeding the output of the first computation as the input to the next computation: > -- End-to-end > > aToB :: A -> ListT IO B > bToC :: B -> ListT IO C > > -- Combined computation > > aToC :: A -> LIstT IO C > aToC = aToB >=> bToC ... or you can just use @do@ notation if you prefer. However, the `Pipe` type is more general than `ListT` and can represent things like termination. Therefore you should consider mixing `Pipe`s with `ListT` when you need to take advantage of these extra features: > -- Mix ListT with Pipes > > example :: In -> ListT IO Out > > pipe :: Pipe In Out IO () > pipe = Pipes.takeWhile (not . isC) >-> loop example > where > isC (InC _) = True > isC _ = False So promote your `ListT` logic to a `Pipe` when you need to take advantage of these `Pipe`-specific features. -} {- $tricks @pipes@ is more powerful than meets the eye so this section presents some non-obvious tricks you may find useful. Many pipe combinators will work on unusual pipe types and the next few examples will use the 'cat' pipe to demonstrate this. For example, you can loop over the output of a 'Pipe' using 'for', which is how 'P.map' is defined: > map :: Monad m => (a -> b) -> Pipe a b m r > map f = for cat $ \x -> yield (f x) > > -- Read this as: For all values flowing downstream, apply 'f' This is equivalent to: > map f = forever $ do > x <- await > yield (f x) You can also feed a 'Pipe' input using ('>~'). This means we could have instead defined the @yes@ pipe like this: > yes :: Monad m => Producer String m r > yes = return "y" >~ cat > > -- Read this as: Keep feeding "y" downstream This is equivalent to: > yes = forever $ yield "y" You can also sequence two 'Pipe's together. This is how 'P.drop' is defined: > drop :: Monad m => Int -> Pipe a a m r > drop n = do > replicateM_ n await > cat This is equivalent to: > drop n = do > replicateM_ n await > forever $ do > x <- await > yield x You can even compose pipes inside of another pipe: > customerService :: Producer String IO () > customerService = do > each [ "Hello, how can I help you?" -- Begin with a script > , "Hold for one second." > ] > P.stdinLn >-> P.takeWhile (/= "Goodbye!") -- Now continue with a human Also, you can often use 'each' in conjunction with ('~>') to traverse nested data structures. For example, you can print all non-'Nothing' elements from a doubly-nested list: >>> runEffect $ (each ~> each ~> each ~> lift . print) [[Just 1, Nothing], [Just 2, Just 3]] 1 2 3 Another neat thing to know is that 'every' has a more general type: @ 'every' :: ('Monad' m, 'Enumerable' t) => t m a -> 'Producer' a m () @ 'Enumerable' generalizes 'Foldable' and if you have an effectful container of your own that you want others to traverse using @pipes@, just have your container implement the 'toListT' method of the 'Enumerable' class: > class Enumerable t where > toListT :: Monad m => t m a -> ListT m a You can even use 'Enumerable' to traverse effectful types that are not even proper containers, like 'Control.Monad.Trans.Maybe.MaybeT': > input :: MaybeT IO String > input = do > str <- lift getLine > guard (str /= "Fail") > return str >>> runEffect $ every input >-> P.stdoutLn Test Test >>> runEffect $ every input >-> P.stdoutLn Fail >>> -} {- $conclusion This tutorial covers the concepts of connecting, building, and reading @pipes@ code. However, this library is only the core component in an ecosystem of streaming components. Derived libraries that build immediately upon @pipes@ include: * @pipes-concurrency@: Concurrent reactive programming and message passing * @pipes-parse@: Minimal utilities for stream parsing * @pipes-safe@: Resource management and exception safety for @pipes@ * @pipes-group@: Grouping streams in constant space These libraries provide functionality specialized to common streaming domains. Additionally, there are several libraries on Hackage that provide even higher-level functionality, which you can find by searching under the \"Pipes\" category or by looking for packages with a @pipes-@ prefix in their name. Current examples include: * @pipes-extras@: Miscellaneous utilities * @pipes-network@/@pipes-network-tls@: Networking * @pipes-zlib@: Compression and decompression * @pipes-binary@: Binary serialization * @pipes-attoparsec@: High-performance parsing * @pipes-aeson@: JSON serialization and deserialization Even these derived packages still do not explore the full potential of @pipes@ functionality, which actually permits bidirectional communication. Advanced @pipes@ users can explore this library in greater detail by studying the documentation in the "Pipes.Core" module to learn about the symmetry of the underlying 'Proxy' type and operators. To learn more about @pipes@, ask questions, or follow @pipes@ development, you can subscribe to the @haskell-pipes@ mailing list at: ... or you can mail the list directly at: Additionally, for questions regarding types or type errors, you might find the following appendix on types very useful. -} {- $types @pipes@ uses parametric polymorphism (i.e. generics) to overload all operations. You've probably noticed this overloading already: * 'yield' works within both 'Producer's and 'Pipe's * 'await' works within both 'Consumer's and 'Pipe's * ('>->') connects 'Producer's, 'Consumer's, and 'Pipe's in varying ways This overloading is great when it works, but when connections fail they produce type errors that appear intimidating at first. This section explains the underlying types so that you can work through type errors intelligently. 'Producer's, 'Consumer's, 'Pipe's, and 'Effect's are all special cases of a single underlying type: a 'Proxy'. This overarching type permits fully bidirectional communication on both an upstream and downstream interface. You can think of it as having the following shape: > Proxy a' a b' b m r > > Upstream | Downstream > +---------+ > | | > a' <== <== b' -- Information flowing upstream > | | > a ==> ==> b -- Information flowing downstream > | | | > +----|----+ > v > r The four core types do not use the upstream flow of information. This means that the @a'@ and @b'@ in the above diagram go unused unless you use the more advanced features provided in "Pipes.Core". @pipes@ uses type synonyms to hide unused inputs or outputs and clean up type signatures. These type synonyms come in two flavors: * Concrete type synonyms that explicitly close unused inputs and outputs of the 'Proxy' type * Polymorphic type synonyms that don't explicitly close unused inputs or outputs The concrete type synonyms use @()@ to close unused inputs and 'X' (the uninhabited type) to close unused outputs: * 'Effect': explicitly closes both ends, forbidding 'await's and 'yield's > type Effect = Proxy X () () X > > Upstream | Downstream > +---------+ > | | > X <== <== () > | | > () ==> ==> X > | | | > +----|----+ > v > r * 'Producer': explicitly closes the upstream end, forbidding 'await's > type Producer b = Proxy X () () b > > Upstream | Downstream > +---------+ > | | > X <== <== () > | | > () ==> ==> b > | | | > +----|----+ > v > r * 'Consumer': explicitly closes the downstream end, forbidding 'yield's > type Consumer a = Proxy () a () X > > Upstream | Downstream > +---------+ > | | > () <== <== () > | | > a ==> ==> X > | | | > +----|----+ > v > r * 'Pipe': marks both ends open, allowing both 'await's and 'yield's > type Pipe a b = Proxy () a () b > > Upstream | Downstream > +---------+ > | | > () <== <== () > | | > a ==> ==> b > | | | > +----|----+ > v > r When you compose 'Proxy's using ('>->') all you are doing is placing them side by side and fusing them laterally. For example, when you compose a 'Producer', 'Pipe', and a 'Consumer', you can think of information flowing like this: > Producer Pipe Consumer > +-----------+ +----------+ +------------+ > | | | | | | > X <== <== () <== <== () <== <== () > | stdinLn | | take 3 | | stdoutLn | > () ==> ==> String ==> ==> String ==> ==> X > | | | | | | | | | > +-----|-----+ +----|-----+ +------|-----+ > v v v > () () () Composition fuses away the intermediate interfaces, leaving behind an 'Effect': > Effect > +-----------------------------------+ > | | > X <== <== () > | stdinLn >-> take 3 >-> stdoutLn | > () ==> ==> X > | | > +----------------|------------------+ > v > () @pipes@ also provides polymorphic type synonyms with apostrophes at the end of their names. These use universal quantification to leave open any unused input or output ends (which I mark using @*@): * 'Producer'': marks the upstream end unused but still open > type Producer' b m r = forall x' x . Proxy x' x () b m r > > Upstream | Downstream > +---------+ > | | > * <== <== () > | | > * ==> ==> b > | | | > +----|----+ > v > r * 'Consumer'': marks the downstream end unused but still open > type Consumer' a m r = forall y' y . Proxy () a y' y m r > > Upstream | Downstream > +---------+ > | | > () <== <== * > | | > a ==> ==> * > | | | > +----|----+ > v > r * 'Effect'': marks both ends unused but still open > type Effect' m r = forall x' x y' y . Proxy x' x y' y m r > > Upstream | Downstream > +---------+ > | | > * <== <== * > | | > * ==> ==> * > | | | > +----|----+ > v > r Note that there is no polymorphic generalization of a 'Pipe'. Like before, if you compose a 'Producer'', a 'Pipe', and a 'Consumer'': > Producer' Pipe Consumer' > +-----------+ +----------+ +------------+ > | | | | | | > * <== <== () <== <== () <== <== * > | stdinLn | | take 3 | | stdoutLn | > * ==> ==> String ==> ==> String ==> ==> * > | | | | | | | | | > +-----|-----+ +-----|----+ +------|-----+ > v v v > () () () ... they fuse into an 'Effect'': > Effect' > +-----------------------------------+ > | | > * <== <== * > | stdinLn >-> take 3 >-> stdoutLn | > * ==> ==> * > | | > +----------------|------------------+ > v > () Polymorphic type synonyms come in handy when you want to keep the type as general as possible. For example, the type signature for 'yield' uses 'Producer'' to keep the type signature simple while still leaving the upstream input end open: @ 'yield' :: 'Monad' m => a -> 'Producer'' a m () @ This type signature lets us use 'yield' within a 'Pipe', too, because the 'Pipe' type synonym is a special case of the polymorphic 'Producer'' type synonym: @ type 'Producer'' b m r = forall x' x . 'Proxy' x' x () b m r type 'Pipe' a b m r = 'Proxy' () a () b m r @ The same is true for 'await', which uses the polymorphic 'Consumer'' type synonym: @ 'await' :: 'Monad' m => 'Consumer'' a m a @ We can use 'await' within a 'Pipe' because a 'Pipe' is a special case of the polymorphic 'Consumer'' type synonym: @ type 'Consumer'' a m r = forall y' y . 'Proxy' () a y' y m r type 'Pipe' a b m r = 'Proxy' () a () b m r @ However, polymorphic type synonyms cause problems in many other cases: * They usually give the wrong behavior when used as the argument of a function (known as the \"negative\" or \"contravariant\" position) like this: > f :: Producer' a m r -> ... -- Wrong > > f :: Producer a m r -> ... -- Right The former function only accepts polymorphic 'Producer's as arguments. The latter function accepts both polymorphic and concrete 'Producer's, which is probably what you want. * Even when you desire a polymorphic argument, this induces a higher-ranked type, because it translates to a @forall@ which you cannot factor out to the top-level to simplify the type signature: > f :: (forall x' x y' . Proxy x' x y' m r) -> ... These kinds of type signatures require the @RankNTypes@ extension. * Even when you have polymorphic type synonyms as the result of a function (i.e. the \"positive\" or \"covariant\" position), recent versions of @ghc@ such still require the @RankNTypes@ extension. For example, the 'Pipes.Prelude.fromHandle' function from "Pipes.Prelude" requires @RankNTypes@ to compile correctly on @ghc-7.6.3@: > fromHandle :: MonadIO m => Handle -> Producer' String m () * You can't use polymorphic type synonyms inside other type constructors without the @ImpredicativeTypes@ extension: > io :: IO (Producer' a m r) -- Type error without ImpredicativeTypes * You can't partially apply polymorphic type synonyms: > stack :: MaybeT (Producer' a m) r -- Type error In these scenarios you should fall back on the concrete type synonyms, which are better behaved. If concrete type synonyms are unsatisfactory, then ask @ghc@ to infer the most general type signature and use that. For the purposes of debugging type errors you can just remember that: > Input --+ +-- Output > | | > v v > Proxy a' a b' b m r > ^ ^ > | | > +----+-- Ignore these For example, let's say that you try to run the 'P.stdinLn' 'Producer'. This produces the following type error: >>> runEffect P.stdinLn :4:5: Couldn't match expected type `X' with actual type `String' Expected type: Effect m0 r0 Actual type: Proxy X () () String IO () In the first argument of `runEffect', namely `P.stdinLn' In the expression: runEffect P.stdinLn 'runEffect' expects an 'Effect', which is equivalent to the following type: > Effect IO () = Proxy X () () X IO () ... but 'P.stdinLn' type-checks as a 'Producer', which has the following type: > Producer String IO () = Proxy X () () String IO () The fourth type variable (the output) does not match. For an 'Effect' this type variable should be closed (i.e. 'X'), but 'P.stdinLn' has a 'String' output, thus the type error: > Couldn't match expected type `X' with actual type `String' Any time you get type errors like these you can work through them by expanding out the type synonyms and seeing which type variables do not match. You may also consult this table of type synonyms to more easily compare them: > type Effect = Proxy X () () X > type Producer b = Proxy X () () b > type Consumer a = Proxy () a () X > type Pipe a b = Proxy () a () b > > type Server b' b = Proxy X () b' b > type Client a' a = Proxy a' a () X > > type Effect' m r = forall x' x y' y . Proxy x' x y' y m r > type Producer' b m r = forall x' x . Proxy x' x () b m r > type Consumer' a m r = forall y' y . Proxy () a y' y m r > > type Server' b' b m r = forall x' x . Proxy x' x b' b m r > type Client' a' a m r = forall y' y . Proxy a' a y' y m r -} {- $timecomplexity There are three functions that give quadratic time complexity when used in within @pipes@: * 'sequence' * 'replicateM' * 'mapM' For example, the time complexity of this code segment scales quadratically with `n`: > import Control.Monad (replicateM) > import Pipes > > quadratic :: Int -> Consumer a m [a] > quadratic n = replicateM n await These three functions are generally bad practice to use, because all three of them correspond to \"ListT done wrong\", building a list in memory instead of streaming results. However, sometimes situations arise where one deliberately intends to build a list in memory. The solution is to use the \"codensity transformation\" to transform the code to run with linear time complexity. This involves: * wrapping the code in the @Codensity@ monad transformer (from @Control.Monad.Codensity@ module of the @kan-extensions@ package) using 'lift' * applying 'sequence' \/ 'replicateM' \/ 'mapM' * unwrapping the code using @lowerCodensity@ To illustrate this, we'd transform the above example to: > import Control.Monad.Codensity (lowerCodensity) > > linear :: Monad m => Int -> Consumer a m [a] > linear n = lowerCodensity $ replicateM n $ lift await This will produce the exact same result, but in linear time. -} {- $copyright This tutorial is licensed under a -} pipes-4.1.9/tests/Main.hs0000644000000000000000000001674512267121502013430 0ustar0000000000000000module Main (main) where import Data.Function (on) import Data.List (intercalate) import Control.Monad ((>=>)) import Control.Monad.Trans.Writer (Writer, runWriter, tell) import Test.QuickCheck (Gen, Arbitrary(..), choose) import Test.Framework (defaultMain, testGroup, Test) import Test.Framework.Providers.QuickCheck2 (testProperty) import Pipes import Pipes.Core import Prelude hiding (log) main :: IO () main = defaultMain tests tests :: [Test] tests = [ testGroup "Kleisli Category" $ testCategory (>=>) return , testGroup "Respond Category" $ testCategory (/>/) respond ++ [ testProperty "Distributivity" prop_respond_Distributivity ] , testGroup "Request Category" $ testCategory (\>\) request ++ [ testProperty "Distributivity" prop_request_Distributivity , testProperty "Zero Law" prop_request_ZeroLaw ] , testGroup "Pull Category" $ testCategory (>+>) pull , testGroup "Push Category" $ testCategory (>~>) push , testGroup "Push/Pull" [ testProperty "Associativity" prop_pushPull_Associativity ] , testGroup "Duals" [ testGroup "Request" [ testProperty "Composition" prop_dual_RequestComposition , testProperty "Identity" prop_dual_RequestIdentity ] , testGroup "Respond" [ testProperty "Composition" prop_dual_RespondComposition , testProperty "Identity" prop_dual_RespondIdentity ] , testProperty "Distributivity" prop_dual_ReflectDistributivity , testProperty "Zero Law" prop_dual_ReflectZeroLaw , testProperty "Involution" prop_dual_Involution ] , testGroup "Functor Laws" [ testProperty "Identity" prop_FunctorIdentity ] ] arbitraryBoundedEnum' :: (Bounded a, Enum a) => Gen a arbitraryBoundedEnum' = do let mn = minBound mx = maxBound `asTypeOf` mn n <- choose (fromEnum mn, fromEnum mx) return (toEnum n `asTypeOf` mn) data ClientStep = ClientRequest | ClientLog | ClientInc deriving (Enum, Bounded) instance Arbitrary ClientStep where arbitrary = arbitraryBoundedEnum' shrink _ = [] instance Show ClientStep where show x = case x of ClientRequest -> "request" ClientLog -> "log" ClientInc -> "inc" data ServerStep = ServerRespond | ServerLog | ServerInc deriving (Enum, Bounded) instance Arbitrary ServerStep where arbitrary = arbitraryBoundedEnum' shrink _ = [] instance Show ServerStep where show x = case x of ServerRespond -> "respond" ServerLog -> "log" ServerInc -> "inc" data ProxyStep = ProxyRequest | ProxyRespond | ProxyLog | ProxyInc deriving (Enum, Bounded) instance Arbitrary ProxyStep where arbitrary = arbitraryBoundedEnum' shrink _ = [] instance Show ProxyStep where show x = case x of ProxyRequest -> "request" ProxyRespond -> "respond" ProxyLog -> "log" ProxyInc -> "inc" log :: Int -> Proxy a' a b' b (Writer [Int]) Int log n = do lift (tell [n]) return n inc :: (Monad m) => Int -> Proxy a' a b' b m Int inc n = return (n + 1) correct :: String -> String correct str = case str of [] -> "return" _ -> str newtype AClient = AClient { unAClient :: [ClientStep] } instance Arbitrary AClient where arbitrary = fmap AClient arbitrary shrink = map AClient . shrink . unAClient instance Show AClient where show = correct . intercalate " >=> " . map show . unAClient aClient :: AClient -> Int -> Client Int Int (Writer [Int]) Int aClient = foldr (>=>) return . map f . unAClient where f x = case x of ClientRequest -> request ClientLog -> log ClientInc -> inc newtype AServer = AServer { unAServer :: [ServerStep] } instance Arbitrary AServer where arbitrary = fmap AServer arbitrary shrink = map AServer . shrink . unAServer instance Show AServer where show = correct . intercalate " >=> " . map show . unAServer aServer :: AServer -> Int -> Server Int Int (Writer [Int]) Int aServer = foldr (>=>) return . map f . unAServer where f x = case x of ServerRespond -> respond ServerLog -> log ServerInc -> inc newtype AProxy = AProxy { unAProxy :: [ProxyStep] } instance Arbitrary AProxy where arbitrary = fmap AProxy arbitrary shrink = map AProxy . shrink . unAProxy instance Show AProxy where show = correct . intercalate " >=> " . map show . unAProxy aProxy :: AProxy -> Int -> Proxy Int Int Int Int (Writer [Int]) Int aProxy = foldr (>=>) return . map f . unAProxy where f x = case x of ProxyRequest -> request ProxyRespond -> respond ProxyLog -> log ProxyInc -> inc type ProxyK = Int -> Proxy Int Int Int Int (Writer [Int]) Int type Operation = ProxyK -> ProxyK -> ProxyK infix 0 === (===) :: ProxyK -> ProxyK -> AServer -> AClient -> Bool (===) pl pr p0 p1 = let sv = aServer p0 cl = aClient p1 f p = runWriter (runEffect (p 0)) in on (==) f (sv >+> pl >+> cl) (sv >+> pr >+> cl) gen_prop_RightIdentity, gen_prop_LeftIdentity :: Operation -> ProxyK -- right/left identity element -> AProxy -> AServer -> AClient -> Bool gen_prop_RightIdentity (>>>) idt f' = let f = aProxy f' in (f >>> idt) === f gen_prop_LeftIdentity (>>>) idt f' = let f = aProxy f' in (idt >>> f) === f gen_prop_Associativity :: Operation -> AProxy -> AProxy -> AProxy -> AServer -> AClient -> Bool gen_prop_Associativity (>>>) f' g' h' = let f = aProxy f' g = aProxy g' h = aProxy h' in f >>> (g >>> h) === (f >>> g) >>> h testCategory :: Operation -> ProxyK -> [Test] testCategory op idt = [ testProperty "Left Identity" $ gen_prop_LeftIdentity op idt , testProperty "Right Identity" $ gen_prop_RightIdentity op idt , testProperty "Associativity" $ gen_prop_Associativity op ] -- Respond Category prop_respond_Distributivity f' g' h' = let f = aProxy f' g = aProxy g' h = aProxy h' in (f >=> g) />/ h === (f />/ h) >=> (g />/ h) -- Request Category prop_request_Distributivity f' g' h' = let f = aProxy f' g = aProxy g' h = aProxy h' in f \>\ (g >=> h) === (f \>\ g) >=> (f \>\ h) prop_request_ZeroLaw f' = let f = aProxy f' in (f \>\ return) === return -- Push/Pull prop_pushPull_Associativity f' g' h' = let f = aProxy f' g = aProxy g' h = aProxy h' in (f >+> g) >~> h === f >+> (g >~> h) -- Duals prop_dual_RequestComposition f' g' = let f = aProxy f' g = aProxy g' in reflect . (f \>\ g) === reflect . g />/ reflect . f prop_dual_RequestIdentity = reflect . request === respond prop_dual_RespondComposition f' g' = let f = aProxy f' g = aProxy g' in reflect . (f />/ g) === reflect . g \>\ reflect . f prop_dual_RespondIdentity = reflect . respond === request prop_dual_ReflectDistributivity f' g' = let f = aProxy f' g = aProxy g' in reflect . (f >=> g) === reflect . f >=> reflect . g prop_dual_ReflectZeroLaw = reflect . return === return prop_dual_Involution f' = let f = aProxy f' in (reflect . reflect) . f >=> return === f -- Functor Laws prop_FunctorIdentity p' = let p = aProxy p' in fmap id p === id p pipes-4.1.9/benchmarks/LiftBench.hs0000644000000000000000000000373512610577267015367 0ustar0000000000000000{-# LANGUAGE RankNTypes #-} module Main (main) where import Common (commonMain) import Control.DeepSeq import Control.Monad.Identity import qualified Control.Monad.Trans.Reader as R import qualified Control.Monad.Trans.State.Strict as S import Criterion.Main import Data.Monoid import Pipes import Pipes.Lift defaultMax :: Int defaultMax = 10000 main :: IO () main = commonMain defaultMax liftBenchmarks iter :: forall m a . (Monad m , Ord a, Num a) => (a -> m a) -> a -> Effect m a iter a vmax = loop 0 where loop n | n > vmax = return vmax | otherwise = do x <- lift $ a n loop $! x s_bench :: Int -> Effect (S.StateT Int Identity) Int s_bench = iter (\n -> S.get >>= (\a -> S.put $! a + n) >> return (n + 1)) r_bench :: Int -> Effect (R.ReaderT Int Identity) Int r_bench = iter (\n -> R.ask >>= (\a -> return $ n + a)) -- Run before Proxy runB :: (a -> Effect Identity r) -> a -> r runB f a = runIdentity $ runEffect $ f a -- Run after Proxy runA :: (Monad m) => (m r -> Identity a) -> Effect m r -> a runA f a = runIdentity $ f (runEffect a) liftBenchmarks :: Int -> [Benchmark] liftBenchmarks vmax = let applyBench = map ($ vmax) in [ bgroup "ReaderT" $ let defT f = (\d -> f d 1) in applyBench [ bench "runReaderP_B" . whnf (runB (runReaderP 1) . r_bench) , bench "runReaderP_A" . whnf (runA (defT R.runReaderT) . r_bench) ] , bgroup "StateT" $ let defT f = (\s -> f s 0) in applyBench [ bench "runStateP_B" . nf (runB (runStateP 0) . s_bench) , bench "runStateP_A" . nf (runA (defT S.runStateT) . s_bench) , bench "evalStateP_B" . whnf (runB (evalStateP 0) . s_bench) , bench "evalStateP_A" . whnf (runA (defT S.evalStateT) . s_bench) , bench "execStateP_B" . whnf (runB (execStateP 0) . s_bench) , bench "execStateP_A" . whnf (runA (defT S.execStateT) . s_bench) ] ] pipes-4.1.9/benchmarks/Common.hs0000644000000000000000000000136612713420457014747 0ustar0000000000000000module Common (commonMain) where import Criterion.Main (Benchmark, runMode) import Criterion.Main.Options as Criterion import Data.Maybe (fromMaybe) import Options.Applicative commonMain :: Int -- ^ default maximum data size -> (Int -> [Benchmark]) -- ^ the benchmarks to run -> IO () commonMain mdMax bench = do (maybeNewMax, critMode) <- execParser $ info (helper <*> options) mempty runMode critMode $ bench (fromMaybe mdMax maybeNewMax) options :: Parser (Maybe Int, Criterion.Mode) options = (,) <$> optional (option auto (help "benchmark maximum data size" <> metavar "N" <> short 'i' <> long "imax")) <*> Criterion.parseWith Criterion.defaultConfig pipes-4.1.9/benchmarks/PreludeBench.hs0000644000000000000000000000622412267121502016046 0ustar0000000000000000{-# LANGUAGE RankNTypes #-} module Main (main) where import Criterion.Main import Common (commonMain) import Control.Monad.Identity (Identity, runIdentity) import Pipes import qualified Pipes.Prelude as P import Prelude hiding (enumFromTo) defaultMax :: Int defaultMax = 10000 main :: IO () main = commonMain defaultMax preludeBenchmarks enumFromTo :: (Int -> a) -> Int -> Int -> Producer a Identity () enumFromTo f n1 n2 = loop n1 where loop n = if n <= n2 then do yield $! f n loop $! n + 1 else return () {-# INLINABLE enumFromTo #-} drain :: Producer b Identity r -> r drain p = runIdentity $ runEffect $ for p discard msum :: (Monad m) => Producer Int m () -> m Int msum = P.foldM (\a b -> return $ a + b) (return 0) return scanMSum :: (Monad m) => Pipe Int Int m r scanMSum = P.scanM (\x y -> return (x + y)) (return 0) return -- Using runIdentity seems to reduce outlier counts. preludeBenchmarks :: Int -> [Benchmark] preludeBenchmarks vmax = let applyBench b = b benchEnum_p benchEnum_p = enumFromTo id 1 vmax in [ bgroup "Folds" $ map applyBench [ bench "all" . whnf (runIdentity . P.all (<= vmax)) , bench "any" . whnf (runIdentity . P.any (> vmax)) , bench "find" . whnf (runIdentity . P.find (== vmax)) , bench "findIndex" . whnf (runIdentity . P.findIndex (== vmax)) , bench "fold" . whnf (runIdentity . P.fold (+) 0 id) , bench "foldM" . whnf (runIdentity . msum) , bench "head" . nf (runIdentity . P.head) , bench "index" . nf (runIdentity . P.index (vmax-1)) , bench "last" . nf (runIdentity . P.last) , bench "length" . whnf (runIdentity . P.length) , bench "null" . whnf (runIdentity . P.null) , bench "toList" . nf P.toList ] , bgroup "Pipes" $ map applyBench [ bench "chain" . whnf (drain . (>-> P.chain (\_ -> return ()))) , bench "drop" . whnf (drain . (>-> P.drop vmax)) , bench "dropWhile" . whnf (drain . (>-> P.dropWhile (<= vmax))) , bench "filter" . whnf (drain . (>-> P.filter even)) , bench "findIndices" . whnf (drain . (>-> P.findIndices (<= vmax))) , bench "map" . whnf (drain . (>-> P.map id)) , bench "mapM" . whnf (drain . (>-> P.mapM return)) , bench "take" . whnf (drain . (>-> P.take vmax)) , bench "takeWhile" . whnf (drain . (>-> P.takeWhile (<= vmax))) , bench "scan" . whnf (drain . (>-> P.scan (+) 0 id)) , bench "scanM" . whnf (drain . (>-> scanMSum)) ] ++ [ bench "concat" $ whnf (drain . (>-> P.concat)) $ enumFromTo Just 1 vmax ] , bgroup "Zips" $ map applyBench [ bench "zip" . whnf (drain . P.zip benchEnum_p) , bench "zipWith" . whnf (drain . P.zipWith (+) benchEnum_p) ] , bgroup "enumFromTo.vs.each" [ bench "enumFromTo" $ whnf (drain . enumFromTo id 1) vmax , bench "each" $ whnf (drain . each) [1..vmax] ] ] pipes-4.1.9/benchmarks/Common.hs0000644000000000000000000000136612713420457014747 0ustar0000000000000000module Common (commonMain) where import Criterion.Main (Benchmark, runMode) import Criterion.Main.Options as Criterion import Data.Maybe (fromMaybe) import Options.Applicative commonMain :: Int -- ^ default maximum data size -> (Int -> [Benchmark]) -- ^ the benchmarks to run -> IO () commonMain mdMax bench = do (maybeNewMax, critMode) <- execParser $ info (helper <*> options) mempty runMode critMode $ bench (fromMaybe mdMax maybeNewMax) options :: Parser (Maybe Int, Criterion.Mode) options = (,) <$> optional (option auto (help "benchmark maximum data size" <> metavar "N" <> short 'i' <> long "imax")) <*> Criterion.parseWith Criterion.defaultConfig pipes-4.1.9/LICENSE0000644000000000000000000000276412270345217012054 0ustar0000000000000000Copyright (c) 2012-2014 Gabriel Gonzalez All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * 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. * Neither the name of Gabriel Gonzalez nor the names of other contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT OWNER 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. pipes-4.1.9/Setup.hs0000644000000000000000000000005612152520554012471 0ustar0000000000000000import Distribution.Simple main = defaultMain pipes-4.1.9/pipes.cabal0000644000000000000000000000651412713420571013147 0ustar0000000000000000Name: pipes Version: 4.1.9 Cabal-Version: >= 1.10 Build-Type: Simple License: BSD3 License-File: LICENSE Copyright: 2012-2014 Gabriel Gonzalez Author: Gabriel Gonzalez Maintainer: Gabriel439@gmail.com Bug-Reports: https://github.com/Gabriel439/Haskell-Pipes-Library/issues Synopsis: Compositional pipelines Description: `pipes` is a clean and powerful stream processing library that lets you build and connect reusable streaming components . Advantages over traditional streaming libraries: . * /Concise API/: Use simple commands like 'for', ('>->'), 'await', and 'yield' . * /Blazing fast/: Implementation tuned for speed, including shortcut fusion . * /Lightweight Dependency/: @pipes@ is small and compiles very rapidly, including dependencies . * /Elegant semantics/: Use practical category theory . * /ListT/: Correct implementation of 'ListT' that interconverts with pipes . * /Bidirectionality/: Implement duplex channels . * /Extensive Documentation/: Second to none! . Import "Pipes" to use the library. . Read "Pipes.Tutorial" for an extensive tutorial. Category: Control, Pipes Source-Repository head Type: git Location: https://github.com/Gabriel439/Haskell-Pipes-Library Library Default-Language: Haskell2010 HS-Source-Dirs: src Build-Depends: base >= 4.4 && < 5 , transformers >= 0.2.0.0 && < 0.6, mmorph >= 1.0.0 && < 1.1, mtl >= 2.1 && < 2.3 Exposed-Modules: Pipes, Pipes.Core, Pipes.Internal, Pipes.Lift, Pipes.Prelude, Pipes.Tutorial GHC-Options: -O2 -Wall Benchmark prelude-benchmarks Default-Language: Haskell2010 Type: exitcode-stdio-1.0 HS-Source-Dirs: benchmarks Main-Is: PreludeBench.hs Other-Modules: Common GHC-Options: -O2 -Wall -rtsopts -fno-warn-unused-do-bind Build-Depends: base >= 4.4 && < 5 , criterion >= 1.1.1.0 && < 1.2, optparse-applicative >= 0.12 && < 0.13, mtl >= 2.1 && < 2.3, pipes >= 4.0.0 && < 4.2 test-suite tests Default-Language: Haskell2010 Type: exitcode-stdio-1.0 HS-Source-Dirs: tests Main-Is: Main.hs GHC-Options: -Wall -rtsopts -fno-warn-missing-signatures -fno-enable-rewrite-rules Build-Depends: base >= 4.4 && < 5 , pipes >= 4.0.0 && < 4.2 , QuickCheck >= 2.4 && < 3 , mtl >= 2.1 && < 2.3 , test-framework >= 0.4 && < 1 , test-framework-quickcheck2 >= 0.2.0 && < 0.4 , transformers >= 0.2.0.0 && < 0.6 Benchmark lift-benchmarks Default-Language: Haskell2010 Type: exitcode-stdio-1.0 HS-Source-Dirs: benchmarks Main-Is: LiftBench.hs Other-Modules: Common GHC-Options: -O2 -Wall -rtsopts -fno-warn-unused-do-bind Build-Depends: base >= 4.4 && < 5 , criterion >= 1.1.1.0 && < 1.2, optparse-applicative >= 0.12 && < 0.13, deepseq >= 1.4.0.0 , mtl >= 2.1 && < 2.3, pipes >= 4.0.0 && < 4.2, transformers >= 0.2.0.0 && < 0.6