Safe Haskell | None |
---|---|
Language | Haskell2010 |
- data Stream f m r
- unfold :: (Monad m, Functor f) => (s -> m (Either r (f s))) -> s -> Stream f m r
- for :: (Monad m, Functor f) => Stream (Of a) m r -> (a -> Stream f m x) -> Stream f m r
- construct :: (forall b. (f b -> b) -> (m b -> b) -> (r -> b) -> b) -> Stream f m r
- maps :: (Monad m, Functor f) => (forall x. f x -> g x) -> Stream f m r -> Stream g m r
- maps' :: (Monad m, Functor f) => (forall x. f x -> m (a, x)) -> Stream f m r -> Stream (Of a) m r
- mapsM :: (Monad m, Functor f) => (forall x. f x -> m (g x)) -> Stream f m r -> Stream g m r
- inspect :: (Functor f, Monad m) => Stream f m r -> m (Either r (f (Stream f m r)))
- destroy :: (Functor f, Monad m) => Stream f m r -> (f b -> b) -> (m b -> b) -> (r -> b) -> b
- intercalates :: (Monad m, Monad (t m), MonadTrans t) => t m a -> Stream (t m) m b -> t m b
- concats :: (MonadTrans t, Monad (t m), Monad m) => Stream (t m) m a -> t m a
- iterTM :: (Functor f, Monad m, MonadTrans t, Monad (t m)) => (f (t m a) -> t m a) -> Stream f m a -> t m a
- iterT :: (Functor f, Monad m) => (f (m a) -> m a) -> Stream f m a -> m a
- split :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m (Stream f m r)
- chunksOf :: (Monad m, Functor f) => Int -> Stream f m r -> Stream (Stream f m) m r
- concats :: (MonadTrans t, Monad (t m), Monad m) => Stream (t m) m a -> t m a
- data Of a b = !a :> b
- lazily :: Of a b -> (a, b)
- strictly :: (a, b) -> Of a b
- class MFunctor t where
- class MonadTrans t where
Free monad transformer
The Stream
data type is equivalent to FreeT
and can represent any effectful
succession of steps, where the form of the steps or commands
is
specified by the first (functor) parameter.
data Stream f m r = Step !(f (Stream f m r)) | Delay (m (Stream f m r)) | Return r
In the simplest case, the base functor is (,) a
. Here the news
or command at each step is an individual element of type a
,
i.e. a yield
statement. In Prelude
, (a,b)
is
replaced by the left-strict pair Of a b
. Various operations are
defined for types like
Stream (Of a) m r -- a producer in the pipes sense -- i.e. an effectful, streaming [a], or rather ([a],r) Stream (Of a) m (Stream (Of a) m r) -- the effectful splitting of a producer -- i.e. an effectful ([a],[a]) or rather ([a],([a],r)) Stream (Stream (Of a) m) m r -- successive, segmentation of a producer
- - i.e. [[a]], or ([a],([a],([a]... r))) and so on. But of course any functor can be used.
To avoid breaking reasoning principles, the constructors
should not be used directly. A pattern-match should go by way of inspect
- or, in the producer case, next
The constructors are exported by the Internal
module.
Functor f => MFunctor (Stream f) Source | |
Functor f => MMonad (Stream f) Source | |
Functor f => MonadTrans (Stream f) Source | |
(Functor f, Monad m) => Monad (Stream f m) Source | |
(Functor f, Monad m) => Functor (Stream f m) Source | |
(Functor f, Monad m) => Applicative (Stream f m) Source | |
(MonadIO m, Functor f) => MonadIO (Stream f m) Source | |
(Eq r, Eq (m (Stream f m r)), Eq (f (Stream f m r))) => Eq (Stream f m r) Source | |
(Typeable (* -> *) f, Typeable (* -> *) m, Data r, Data (m (Stream f m r)), Data (f (Stream f m r))) => Data (Stream f m r) Source | |
(Show r, Show (m (Stream f m r)), Show (f (Stream f m r))) => Show (Stream f m r) Source |
Constructing a Stream
on a base functor
unfold :: (Monad m, Functor f) => (s -> m (Either r (f s))) -> s -> Stream f m r Source
Build a Stream
by unfolding steps starting from a seed.
unfold inspect = id -- modulo the quotient we work with unfold Pipes.next :: Monad m => Producer a m r -> Stream ((,) a) m r unfold (curry (:>) . Pipes.next) :: Monad m => Producer a m r -> Stream (Of a) m r
for :: (Monad m, Functor f) => Stream (Of a) m r -> (a -> Stream f m x) -> Stream f m r Source
for
replaces each element of a stream with an associated stream. Note that the
associated stream may layer any functor.
construct :: (forall b. (f b -> b) -> (m b -> b) -> (r -> b) -> b) -> Stream f m r Source
Reflect a church-encoded stream; cp. GHC.Exts.build
Transforming streams
maps :: (Monad m, Functor f) => (forall x. f x -> g x) -> Stream f m r -> Stream g m r Source
Map layers of one functor to another with a natural transformation
maps' :: (Monad m, Functor f) => (forall x. f x -> m (a, x)) -> Stream f m r -> Stream (Of a) m r Source
Map free layers of a functor to a corresponding stream of individual elements. This
simplifies the use of folds marked with a ''' in Streaming.Prelude
maps' sum' :: (Monad m, Num a) => Stream (Stream (Of a) m) m r -> Stream (Of a) m r maps' (Pipes.fold' (+) (0::Int) id) :: Monad m => Stream (Producer Int m) m r -> Stream (Of Int) m r
mapsM :: (Monad m, Functor f) => (forall x. f x -> m (g x)) -> Stream f m r -> Stream g m r Source
Map layers of one functor to another with a transformation involving the base monad
Inspecting a stream
inspect :: (Functor f, Monad m) => Stream f m r -> m (Either r (f (Stream f m r))) Source
Inspect the first stage of a freely layered sequence.
Compare Pipes.next
and the replica Streaming.Prelude.next
.
This is the uncons
for the general unfold
.
unfold inspect = id Streaming.Prelude.unfoldr StreamingPrelude.next = id
Eliminating a Stream
destroy :: (Functor f, Monad m) => Stream f m r -> (f b -> b) -> (m b -> b) -> (r -> b) -> b Source
Map a stream to its church encoding; compare list foldr
intercalates :: (Monad m, Monad (t m), MonadTrans t) => t m a -> Stream (t m) m b -> t m b Source
iterTM :: (Functor f, Monad m, MonadTrans t, Monad (t m)) => (f (t m a) -> t m a) -> Stream f m a -> t m a Source
Splitting and joining Stream
s
Useful functors
A left-strict pair; the base functor for streams of individual elements.
!a :> b infixr 4 |
re-exports
class MFunctor t where
A functor in the category of monads, using hoist
as the analog of fmap
:
hoist (f . g) = hoist f . hoist g hoist id = id
hoist :: Monad m => (forall a. m a -> n a) -> t m b -> t n b
Lift a monad morphism from m
to n
into a monad morphism from
(t m)
to (t n)
MFunctor ListT | |
MFunctor Backwards | |
MFunctor MaybeT | |
MFunctor IdentityT | |
MFunctor Lift | |
MFunctor (ReaderT r) | |
MFunctor (StateT s) | |
MFunctor (StateT s) | |
MFunctor (ExceptT e) | |
MFunctor (ErrorT e) | |
MFunctor (WriterT w) | |
MFunctor (WriterT w) | |
MFunctor (Product f) | |
Functor f => MFunctor (Compose f) | |
Functor f => MFunctor (Stream f) | |
MFunctor (RWST r w s) | |
MFunctor (RWST r w s) |
class MonadTrans t where
The class of monad transformers. Instances should satisfy the
following laws, which state that lift
is a monad transformation:
MonadTrans ListT | |
MonadTrans MaybeT | |
MonadTrans IdentityT | |
MonadTrans (ReaderT r) | |
MonadTrans (StateT s) | |
MonadTrans (StateT s) | |
MonadTrans (ExceptT e) | |
Error e => MonadTrans (ErrorT e) | |
Monoid w => MonadTrans (WriterT w) | |
Monoid w => MonadTrans (WriterT w) | |
Functor f => MonadTrans (Stream f) | |
Monoid w => MonadTrans (RWST r w s) | |
Monoid w => MonadTrans (RWST r w s) |