Safe Haskell | Trustworthy |
---|---|
Language | Haskell2010 |
Streaming.Internal
Contents
- data Stream f m r
- unfold :: (Monad m, Functor f) => (s -> m (Either r (f s))) -> s -> Stream f m r
- replicates :: (Monad m, Functor f) => Int -> f () -> Stream f m ()
- repeats :: (Monad m, Functor f) => f () -> Stream f m r
- repeatsM :: (Monad m, Functor f) => m (f ()) -> Stream f m r
- effect :: (Monad m, Functor f) => m (Stream f m r) -> Stream f m r
- wrap :: (Monad m, Functor f) => f (Stream f m r) -> Stream f m r
- yields :: (Monad m, Functor f) => f r -> Stream f m r
- streamBuild :: (forall b. (r -> b) -> (m b -> b) -> (f b -> b) -> b) -> Stream f m r
- cycles :: (Monad m, Functor f) => Stream f m () -> Stream f m r
- delays :: (MonadIO m, Applicative f) => Double -> Stream f m r
- never :: (Monad m, Applicative f) => Stream f m r
- untilJust :: (Monad m, Applicative f) => m (Maybe r) -> Stream f m r
- intercalates :: (Monad m, Monad (t m), MonadTrans t) => t m x -> Stream (t m) m r -> t m r
- concats :: (Monad m, Functor f) => Stream (Stream f m) m r -> Stream f m r
- iterT :: (Functor f, Monad m) => (f (m a) -> m a) -> Stream f m a -> 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
- destroy :: (Functor f, Monad m) => Stream f m r -> (f b -> b) -> (m b -> b) -> (r -> b) -> b
- streamFold :: (Functor f, Monad m) => (r -> b) -> (m b -> b) -> (f b -> b) -> Stream f m r -> b
- inspect :: (Functor f, Monad m) => Stream f m r -> m (Either r (f (Stream f m r)))
- maps :: (Monad m, Functor f) => (forall x. f x -> g x) -> Stream f m r -> Stream g m r
- mapsM :: (Monad m, Functor f) => (forall x. f x -> m (g x)) -> Stream f m r -> Stream g m r
- decompose :: (Monad m, Functor f) => Stream (Compose m f) m r -> Stream f m r
- mapsM_ :: (Functor f, Monad m) => (forall x. f x -> m x) -> Stream f m r -> m r
- run :: Monad m => Stream m m r -> m r
- distribute :: (Monad m, Functor f, MonadTrans t, MFunctor t, Monad (t (Stream f m))) => Stream f (t m) r -> t (Stream f m) r
- groups :: (Monad m, Functor f, Functor g) => Stream (Sum f g) m r -> Stream (Sum (Stream f m) (Stream g m)) m r
- chunksOf :: (Monad m, Functor f) => Int -> Stream f m r -> Stream (Stream f m) m r
- splitsAt :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m (Stream f m r)
- takes :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m ()
- cutoff :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m (Maybe r)
- zipsWith :: (Monad m, Functor f, Functor g, Functor h) => (forall x y. f x -> g y -> h (x, y)) -> Stream f m r -> Stream g m r -> Stream h m r
- zips :: (Monad m, Functor f, Functor g) => Stream f m r -> Stream g m r -> Stream (Compose f g) m r
- unzips :: (Monad m, Functor f, Functor g) => Stream (Compose f g) m r -> Stream f (Stream g m) r
- interleaves :: (Monad m, Applicative h) => Stream h m r -> Stream h m r -> Stream h m r
- separate :: (Monad m, Functor f, Functor g) => Stream (Sum f g) m r -> Stream f (Stream g m) r
- unseparate :: (Monad m, Functor f, Functor g) => Stream f (Stream g m) r -> Stream (Sum f g) m r
- switch :: Sum f g r -> Sum g f r
- bracketStream :: (Functor f, MonadResource m) => IO a -> (a -> IO ()) -> (a -> Stream f m b) -> Stream f m b
- unexposed :: (Functor f, Monad m) => Stream f m r -> Stream f m r
- hoistExposed :: (Functor f, Monad m1) => (m1 (Stream f m r) -> m (Stream f m r)) -> Stream f m1 r -> Stream f m r
- mapsExposed :: (Monad m, Functor f) => (forall x. f x -> g x) -> Stream f m r -> Stream g m r
- mapsMExposed :: (Functor f1, Monad m) => (f1 (Stream f m r) -> m (f (Stream f m r))) -> Stream f1 m r -> Stream f m r
- destroyExposed :: (Functor f, Monad m) => Stream f m t -> (f b -> b) -> (m b -> b) -> (t -> b) -> b
The 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)) | Effect (m (Stream f m r)) | Return r
The producer concept uses the simple functor (a,_)
- or the stricter
Of a _
. Then the news at each step or layer is just: an individual item of type a
.
Since Stream (Of a) m r
is equivalent to Pipe.Producer a m r
, much of
the pipes
Prelude
can easily be mirrored in a streaming
Prelude
. Similarly,
a simple Consumer a m r
or Parser a m r
concept arises when the base functor is
(a -> _)
. Stream ((->) input) m result
consumes input
until it returns a
result
.
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.
Instances
Introducing a stream
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. See also
the specialized unfoldr
in the prelude.
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
replicates :: (Monad m, Functor f) => Int -> f () -> Stream f m () Source #
Repeat a functorial layer, command or instruction a fixed number of times.
replicates n = takes n . repeats
repeats :: (Monad m, Functor f) => f () -> Stream f m r Source #
Repeat a functorial layer (a "command" or "instruction") forever.
repeatsM :: (Monad m, Functor f) => m (f ()) -> Stream f m r Source #
Repeat an effect containing a functorial layer, command or instruction forever.
effect :: (Monad m, Functor f) => m (Stream f m r) -> Stream f m r Source #
Wrap an effect that returns a stream
effect = join . lift
wrap :: (Monad m, Functor f) => f (Stream f m r) -> Stream f m r Source #
Wrap a new layer of a stream. So, e.g.
S.cons :: Monad m => a -> Stream (Of a) m r -> Stream (Of a) m r S.cons a str = wrap (a :> str)
and, recursively:
S.each :: (Monad m, Foldable t) => t a -> Stream (Of a) m () S.each = foldr (\a b -> wrap (a :> b)) (return ())
The two operations
wrap :: (Monad m, Functor f ) => f (Stream f m r) -> Stream f m r effect :: (Monad m, Functor f ) => m (Stream f m r) -> Stream f m r
are fundamental. We can define the parallel operations yields
and lift
in
terms of them
yields :: (Monad m, Functor f ) => f r -> Stream f m r yields = wrap . fmap return lift :: (Monad m, Functor f ) => m r -> Stream f m r lift = effect . fmap return
yields :: (Monad m, Functor f) => f r -> Stream f m r Source #
yields
is like lift
for items in the streamed functor.
It makes a singleton or one-layer succession.
lift :: (Monad m, Functor f) => m r -> Stream f m r yields :: (Monad m, Functor f) => f r -> Stream f m r
Viewed in another light, it is like a functor-general version of yield
:
S.yield a = yields (a :> ())
streamBuild :: (forall b. (r -> b) -> (m b -> b) -> (f b -> b) -> b) -> Stream f m r Source #
Reflect a church-encoded stream; cp. GHC.Exts.build
streamFold return_ effect_ step_ (streamBuild psi) = psi return_ effect_ step_
cycles :: (Monad m, Functor f) => Stream f m () -> Stream f m r Source #
Construct an infinite stream by cycling a finite one
cycles = forever
>>>
never :: (Monad m, Applicative f) => Stream f m r Source #
never
interleaves the pure applicative action with the return of the monad forever.
It is the empty
of the Alternative
instance, thus
never <|> a = a a <|> never = a
and so on. If w is a monoid then never :: Stream (Of w) m r
is
the infinite sequence of mempty
, and
str1 <|> str2
appends the elements monoidally until one of streams ends.
Thus we have, e.g.
>>>
S.stdoutLn $ S.take 2 $ S.stdinLn <|> S.repeat " " <|> S.stdinLn <|> S.repeat " " <|> S.stdinLn
1<Enter> 2<Enter> 3<Enter> 1 2 3 4<Enter> 5<Enter> 6<Enter> 4 5 6
This is equivalent to
>>>
S.stdoutLn $ S.take 2 $ foldr (<|>) never [S.stdinLn, S.repeat " ", S.stdinLn, S.repeat " ", S.stdinLn ]
Where f
is a monad, (<|>)
sequences the conjoined streams stepwise. See the
definition of paste
here,
where the separate steps are bytestreams corresponding to the lines of a file.
Given, say,
data Branch r = Branch r r deriving Functor -- add obvious applicative instance
then never :: Stream Branch Identity r
is the pure infinite binary tree with
(inaccessible) r
s in its leaves. Given two binary trees, tree1 <|> tree2
intersects them, preserving the leaves that came first,
so tree1 <|> never = tree1
Stream Identity m r
is an action in m
that is indefinitely delayed. Such an
action can be constructed with e.g. untilJust
.
untilJust :: (Monad m, Applicative f) => m (Maybe r) -> Stream f m r
Given two such items, <|>
instance races them.
It is thus the iterative monad transformer specially defined in
Control.Monad.Trans.Iter
So, for example, we might write
>>>
let justFour str = if length str == 4 then Just str else Nothing
>>>
let four = untilJust (liftM justFour getLine)
>>>
run four
one<Enter> two<Enter> three<Enter> four<Enter> "four"
The Alternative
instance in
Control.Monad.Trans.Free
is avowedly wrong, though no explanation is given for this.
Eliminating a stream
intercalates :: (Monad m, Monad (t m), MonadTrans t) => t m x -> Stream (t m) m r -> t m r Source #
Interpolate a layer at each segment. This specializes to e.g.
intercalates :: (Monad m, Functor f) => Stream f m () -> Stream (Stream f m) m r -> Stream f m r
concats :: (Monad m, Functor f) => Stream (Stream f m) m r -> Stream f m r Source #
Dissolves the segmentation into layers of Stream f m
layers.
iterT :: (Functor f, Monad m) => (f (m a) -> m a) -> Stream f m a -> m a Source #
Specialized fold following the usage of Control.Monad.Trans.Free
iterT alg = streamFold return join alg
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 #
Specialized fold following the usage of Control.Monad.Trans.Free
iterTM alg = streamFold return (join . lift)
destroy :: (Functor f, Monad m) => Stream f m r -> (f b -> b) -> (m b -> b) -> (r -> b) -> b Source #
Map a stream directly to its church encoding; compare Data.List.foldr
streamFold :: (Functor f, Monad m) => (r -> b) -> (m b -> b) -> (f b -> b) -> Stream f m r -> b Source #
streamFold
reorders the arguments of destroy
to be more akin
to foldr
It is more convenient to query in ghci to figure out
what kind of 'algebra' you need to write.
>>>
:t streamFold return join
(Monad m, Functor f) => (f (m a) -> m a) -> Stream f m a -> m a -- iterT
>>>
:t streamFold return (join . lift)
(Monad m, Monad (t m), Functor f, MonadTrans t) => (f (t m a) -> t m a) -> Stream f m a -> t m a -- iterTM
>>>
:t streamFold return effect
(Monad m, Functor f, Functor g) => (f (Stream g m r) -> Stream g m r) -> Stream f m r -> Stream g m r
>>>
:t \f -> streamFold return effect (wrap . f)
(Monad m, Functor f, Functor g) => (f (Stream g m a) -> g (Stream g m a)) -> Stream f m a -> Stream g m a -- maps
>>>
:t \f -> streamFold return effect (effect . liftM wrap . f)
(Monad m, Functor f, Functor g) => (f (Stream g m a) -> m (g (Stream g m a))) -> Stream f m a -> Stream g m a -- mapped
Inspecting a stream wrap by wrap
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
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 transformation. Compare
hoist, which has a similar effect on the monadic
parameter.
maps id = id maps f . maps g = maps (f . g)
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
maps
is more fundamental than mapsM
, which is best understood as a convenience
for effecting this frequent composition:
mapsM phi = decompose . maps (Compose . phi)
The streaming prelude exports the same function under the better name mapped
,
which overlaps with the lens libraries.
decompose :: (Monad m, Functor f) => Stream (Compose m f) m r -> Stream f m r Source #
Rearrange a succession of layers of the form Compose m (f x)
.
we could as well define decompose
by mapsM
:
decompose = mapped getCompose
but mapped
is best understood as:
mapped phi = decompose . maps (Compose . phi)
since maps
and hoist
are the really fundamental operations that preserve the
shape of the stream:
maps :: (Monad m, Functor f) => (forall x. f x -> g x) -> Stream f m r -> Stream g m r hoist :: (Monad m, Functor f) => (forall a. m a -> n a) -> Stream f m r -> Stream f n r
mapsM_ :: (Functor f, Monad m) => (forall x. f x -> m x) -> Stream f m r -> m r Source #
Map each layer to an effect, and run them all.
run :: Monad m => Stream m m r -> m r Source #
Run the effects in a stream that merely layers effects.
distribute :: (Monad m, Functor f, MonadTrans t, MFunctor t, Monad (t (Stream f m))) => Stream f (t m) r -> t (Stream f m) r Source #
Make it possible to 'run' the underlying transformed monad.
groups :: (Monad m, Functor f, Functor g) => Stream (Sum f g) m r -> Stream (Sum (Stream f m) (Stream g m)) m r Source #
Group layers in an alternating stream into adjoining sub-streams of one type or another.
Splitting streams
chunksOf :: (Monad m, Functor f) => Int -> Stream f m r -> Stream (Stream f m) m r Source #
Break a stream into substreams each with n functorial layers.
>>>
S.print $ mapped S.sum $ chunksOf 2 $ each [1,1,1,1,1]
2 2 1
splitsAt :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m (Stream f m r) Source #
Split a succession of layers after some number, returning a streaming or effectful pair.
>>>
rest <- S.print $ S.splitAt 1 $ each [1..3]
1>>>
S.print rest
2 3
splitAt 0 = return splitAt n >=> splitAt m = splitAt (m+n)
Thus, e.g.
>>>
rest <- S.print $ splitsAt 2 >=> splitsAt 2 $ each [1..5]
1 2 3 4>>>
S.print rest
5
Zipping and unzipping streams
zipsWith :: (Monad m, Functor f, Functor g, Functor h) => (forall x y. f x -> g y -> h (x, y)) -> Stream f m r -> Stream g m r -> Stream h m r Source #
zips :: (Monad m, Functor f, Functor g) => Stream f m r -> Stream g m r -> Stream (Compose f g) m r Source #
unzips :: (Monad m, Functor f, Functor g) => Stream (Compose f g) m r -> Stream f (Stream g m) r Source #
interleaves :: (Monad m, Applicative h) => Stream h m r -> Stream h m r -> Stream h m r Source #
Interleave functor layers, with the effects of the first preceding the effects of the second.
interleaves = zipsWith (liftA2 (,))
>>>
let paste = \a b -> interleaves (Q.lines a) (maps (Q.cons' '\t') (Q.lines b))
>>>
Q.stdout $ Q.unlines $ paste "hello\nworld\n" "goodbye\nworld\n"
hello goodbye world world
separate :: (Monad m, Functor f, Functor g) => Stream (Sum f g) m r -> Stream f (Stream g m) r Source #
Given a stream on a sum of functors, make it a stream on the left functor,
with the streaming on the other functor as the governing monad. This is
useful for acting on one or the other functor with a fold, leaving the
other material for another treatment. It generalizes
partitionEithers
, but actually streams properly.
>>>
let odd_even = S.maps (S.distinguish even) $ S.each [1..10::Int]
>>>
:t separate odd_even
separate odd_even :: Monad m => Stream (Of Int) (Stream (Of Int) m) ()
Now, for example, it is convenient to fold on the left and right values separately:
>>>
S.toList $ S.toList $ separate odd_even
[2,4,6,8,10] :> ([1,3,5,7,9] :> ())
Or we can write them to separate files or whatever:
>>>
runResourceT $ S.writeFile "even.txt" . S.show $ S.writeFile "odd.txt" . S.show $ S.separate odd_even
>>>
:! cat even.txt
2 4 6 8 10>>>
:! cat odd.txt
1 3 5 7 9
Of course, in the special case of Stream (Of a) m r
, we can achieve the above
effects more simply by using copy
>>>
S.toList . S.filter even $ S.toList . S.filter odd $ S.copy $ each [1..10::Int]
[2,4,6,8,10] :> ([1,3,5,7,9] :> ())
But separate
and unseparate
are functor-general.
unseparate :: (Monad m, Functor f, Functor g) => Stream f (Stream g m) r -> Stream (Sum f g) m r Source #
Assorted Data.Functor.x help
switch :: Sum f g r -> Sum g f r Source #
Swap the order of functors in a sum of functors.
>>>
S.toList $ S.print $ separate $ maps S.switch $ maps (S.distinguish (=='a')) $ S.each "banana"
'a' 'a' 'a' "bnn" :> ()>>>
S.toList $ S.print $ separate $ maps (S.distinguish (=='a')) $ S.each "banana"
'b' 'n' 'n' "aaa" :> ()
ResourceT help
bracketStream :: (Functor f, MonadResource m) => IO a -> (a -> IO ()) -> (a -> Stream f m b) -> Stream f m b Source #
For use in implementation
unexposed :: (Functor f, Monad m) => Stream f m r -> Stream f m r Source #
This is akin to the observe
of Pipes.Internal
. It reeffects the layering
in instances of Stream f m r
so that it replicates that of
FreeT
.
hoistExposed :: (Functor f, Monad m1) => (m1 (Stream f m r) -> m (Stream f m r)) -> Stream f m1 r -> Stream f m r Source #
mapsExposed :: (Monad m, Functor f) => (forall x. f x -> g x) -> Stream f m r -> Stream g m r Source #