| Copyright | (c) 2019 Composewell Technologies |
|---|---|
| License | BSD3 |
| Maintainer | streamly@composewell.com |
| Stability | experimental |
| Portability | GHC |
| Safe Haskell | None |
| Language | Haskell2010 |
Streamly.Internal.Data.Unfold
Description
To run the examples in this module:
>>>import qualified Streamly.Data.Fold as Fold>>>import qualified Streamly.Internal.Data.Unfold as Unfold
Unfolds and Streams
An Unfold type is the same as the direct style Stream type except that
it uses an inject function to determine the initial state of the stream
based on an input. A stream is a special case of Unfold when the static
input is unit or Void.
This allows an important optimization to occur in several cases, making the
Unfold a more efficient abstraction. Consider the concatMap and
unfoldMany operations, the latter is more efficient. concatMap
generates a new stream object from each element in the stream by applying
the supplied function to the element, the stream object includes the "step"
function as well as the initial "state" of the stream. Since the stream is
generated dynamically the compiler does not know the step function or the
state type statically at compile time, therefore, it cannot inline it. On
the other hand in case of unfoldMany the compiler has visibility into
the unfold's state generation function, therefore, the compiler knows all
the types statically and it can inline the inject as well as the step
functions, generating efficient code. Essentially, the stream is not opaque
to the consumer in case of unfolds, the consumer knows how to generate the
stream from a seed using a known "inject" and "step" functions.
A Stream is like a data object whereas unfold is like a function. Being
function like, an Unfold is an instance of Category and Arrow type
classes.
Unfolds and Folds
Streams forcing a closed control flow loop can be categorized under two types, unfolds and folds, both of these are duals of each other.
Unfold streams are really generators of a sequence of elements, we can also call them pull style streams. These are lazy producers of streams. On each evaluation the producer generates the next element. A consumer can therefore pull elements from the stream whenever it wants to. A stream consumer can multiplex pull streams by pulling elements from the chosen streams, therefore, pull streams allow merging or multiplexing. On the other hand, with this representation we cannot split or demultiplex a stream. So really these are stream sources that can be generated from a seed and can be merged or zipped into a single stream.
The dual of Unfolds are Folds. Folds can also be called as push style streams or reducers. These are strict consumers of streams. We keep pushing elements to a fold and we can extract the result at any point. A driver can choose which fold to push to and can also push the same element to multiple folds. Therefore, folds allow splitting or demultiplexing a stream. On the other hand, we cannot merge streams using this representation. So really these are stream consumers that reduce the stream to a single value, these consumers can be composed such that a stream can be split over multiple consumers.
Performance:
Composing a tree or graph of computations with unfolds can be much more efficient compared to composing with the Monad instance. The reason is that unfolds allow the compiler to statically know the state and optimize it using stream fusion whereas it is not possible with the monad bind because the state is determined dynamically.
Synopsis
- data Step s a
- data Unfold m a b
- mkUnfoldM :: (s -> m (Step s b)) -> (a -> m s) -> Unfold m a b
- mkUnfoldrM :: Applicative m => (a -> m (Step a b)) -> Unfold m a b
- unfoldrM :: Applicative m => (a -> m (Maybe (b, a))) -> Unfold m a b
- unfoldr :: Applicative m => (a -> Maybe (b, a)) -> Unfold m a b
- functionM :: Applicative m => (a -> m b) -> Unfold m a b
- function :: Applicative m => (a -> b) -> Unfold m a b
- identity :: Applicative m => Unfold m a a
- nilM :: Applicative m => (a -> m c) -> Unfold m a b
- consM :: Applicative m => (a -> m b) -> Unfold m a b -> Unfold m a b
- fromEffect :: Applicative m => m b -> Unfold m a b
- fromPure :: Applicative m => b -> Unfold m a b
- repeatM :: Monad m => Unfold m (m a) a
- replicateM :: Monad m => Int -> Unfold m (m a) a
- fromIndicesM :: Applicative m => (Int -> m a) -> Unfold m Int a
- iterateM :: Monad m => (a -> m a) -> Unfold m (m a) a
- class Enum a => Enumerable a where
- enumerateFrom :: Monad m => Unfold m a a
- enumerateFromTo :: Monad m => Unfold m (a, a) a
- enumerateFromThen :: Monad m => Unfold m (a, a) a
- enumerateFromThenTo :: Monad m => Unfold m (a, a, a) a
- enumerateFromNum :: (Monad m, Num a) => Unfold m a a
- enumerateFromThenNum :: (Monad m, Num a) => Unfold m (a, a) a
- enumerateFromStepNum :: (Monad m, Num a) => Unfold m (a, a) a
- enumerateFromIntegralBounded :: (Monad m, Integral a, Bounded a) => Unfold m a a
- enumerateFromThenIntegralBounded :: (Monad m, Integral a, Bounded a) => Unfold m (a, a) a
- enumerateFromToIntegralBounded :: (Monad m, Integral a, Bounded a) => Unfold m (a, a) a
- enumerateFromThenToIntegralBounded :: (Monad m, Integral a, Bounded a) => Unfold m (a, a, a) a
- enumerateFromIntegral :: (Monad m, Integral a) => Unfold m a a
- enumerateFromThenIntegral :: (Monad m, Integral a) => Unfold m (a, a) a
- enumerateFromToIntegral :: (Monad m, Integral a) => Unfold m (a, a) a
- enumerateFromThenToIntegral :: (Monad m, Integral a) => Unfold m (a, a, a) a
- enumerateFromSmallBounded :: (Monad m, Enum a, Bounded a) => Unfold m a a
- enumerateFromThenSmallBounded :: forall m a. (Monad m, Enum a, Bounded a) => Unfold m (a, a) a
- enumerateFromToSmall :: (Monad m, Enum a) => Unfold m (a, a) a
- enumerateFromThenToSmall :: (Monad m, Enum a) => Unfold m (a, a, a) a
- enumerateFromFractional :: (Monad m, Fractional a) => Unfold m a a
- enumerateFromThenFractional :: (Monad m, Fractional a) => Unfold m (a, a) a
- enumerateFromToFractional :: (Monad m, Fractional a, Ord a) => Unfold m (a, a) a
- enumerateFromThenToFractional :: (Monad m, Fractional a, Ord a) => Unfold m (a, a, a) a
- fromList :: Monad m => Unfold m [a] a
- fromListM :: Monad m => Unfold m [m a] a
- fromStream :: Monad m => Unfold m (SerialT m a) a
- fromStreamK :: Applicative m => Unfold m (Stream m a) a
- fromStreamD :: Applicative m => Unfold m (Stream m a) a
- lmap :: (a -> c) -> Unfold m c b -> Unfold m a b
- lmapM :: Monad m => (a -> m c) -> Unfold m c b -> Unfold m a b
- supply :: a -> Unfold m a b -> Unfold m Void b
- supplyFirst :: a -> Unfold m (a, b) c -> Unfold m b c
- supplySecond :: b -> Unfold m (a, b) c -> Unfold m a c
- discardFirst :: Unfold m a b -> Unfold m (c, a) b
- discardSecond :: Unfold m a b -> Unfold m (a, c) b
- swap :: Unfold m (a, c) b -> Unfold m (c, a) b
- fold :: Monad m => Fold m b c -> Unfold m a b -> a -> m c
- map :: Functor m => (b -> c) -> Unfold m a b -> Unfold m a c
- mapM :: Monad m => (b -> m c) -> Unfold m a b -> Unfold m a c
- mapMWithInput :: Monad m => (a -> b -> m c) -> Unfold m a b -> Unfold m a c
- scanlM' :: Monad m => (b -> a -> m b) -> m b -> Unfold m c a -> Unfold m c b
- scan :: Monad m => Fold m b c -> Unfold m a b -> Unfold m a c
- foldMany :: Fold m b c -> Unfold m a b -> Unfold m a c
- either :: Applicative m => Unfold m a b -> Unfold m (Either a a) (Either b b)
- takeWhileM :: Monad m => (b -> m Bool) -> Unfold m a b -> Unfold m a b
- takeWhile :: Monad m => (b -> Bool) -> Unfold m a b -> Unfold m a b
- take :: Monad m => Int -> Unfold m a b -> Unfold m a b
- filter :: Monad m => (b -> Bool) -> Unfold m a b -> Unfold m a b
- filterM :: Monad m => (b -> m Bool) -> Unfold m a b -> Unfold m a b
- drop :: Monad m => Int -> Unfold m a b -> Unfold m a b
- dropWhile :: Monad m => (b -> Bool) -> Unfold m a b -> Unfold m a b
- dropWhileM :: Monad m => (b -> m Bool) -> Unfold m a b -> Unfold m a b
- zipWithM :: Monad m => (b -> c -> m d) -> Unfold m a b -> Unfold m a c -> Unfold m a d
- zipWith :: Monad m => (b -> c -> d) -> Unfold m a b -> Unfold m a c -> Unfold m a d
- crossWithM :: Monad m => (b -> c -> m d) -> Unfold m a b -> Unfold m a c -> Unfold m a d
- crossWith :: Monad m => (b -> c -> d) -> Unfold m a b -> Unfold m a c -> Unfold m a d
- cross :: Monad m => Unfold m a b -> Unfold m a c -> Unfold m a (b, c)
- apply :: Monad m => Unfold m a (b -> c) -> Unfold m a b -> Unfold m a c
- data ConcatState s1 s2
- = ConcatOuter s1
- | ConcatInner s1 s2
- many :: Monad m => Unfold m a b -> Unfold m b c -> Unfold m a c
- concatMapM :: Monad m => (b -> m (Unfold m a c)) -> Unfold m a b -> Unfold m a c
- bind :: Monad m => Unfold m a b -> (b -> Unfold m a c) -> Unfold m a c
- gbracket_ :: Monad m => (a -> m c) -> (forall s. m s -> m (Either e s)) -> (c -> m d) -> Unfold m (c, e) b -> Unfold m c b -> Unfold m a b
- gbracket :: MonadRunInIO m => (a -> m c) -> (forall s. m s -> m (Either e s)) -> (c -> m d) -> Unfold m (c, e) b -> Unfold m c b -> Unfold m a b
- before :: (a -> m c) -> Unfold m a b -> Unfold m a b
- after :: MonadRunInIO m => (a -> m c) -> Unfold m a b -> Unfold m a b
- after_ :: Monad m => (a -> m c) -> Unfold m a b -> Unfold m a b
- finally :: (MonadAsync m, MonadCatch m) => (a -> m c) -> Unfold m a b -> Unfold m a b
- finally_ :: MonadCatch m => (a -> m c) -> Unfold m a b -> Unfold m a b
- bracket :: (MonadAsync m, MonadCatch m) => (a -> m c) -> (c -> m d) -> Unfold m c b -> Unfold m a b
- bracket_ :: MonadCatch m => (a -> m c) -> (c -> m d) -> Unfold m c b -> Unfold m a b
- onException :: MonadCatch m => (a -> m c) -> Unfold m a b -> Unfold m a b
- handle :: (MonadCatch m, Exception e) => Unfold m e b -> Unfold m a b -> Unfold m a b
Unfold Type
An Unfold m a b is a generator of a stream of values of type b from a
seed of type a in Monad m.
Since: 0.7.0
Unfolds
Basic Constructors
mkUnfoldM :: (s -> m (Step s b)) -> (a -> m s) -> Unfold m a b Source #
Make an unfold from step and inject functions.
Pre-release
mkUnfoldrM :: Applicative m => (a -> m (Step a b)) -> Unfold m a b Source #
unfoldrM :: Applicative m => (a -> m (Maybe (b, a))) -> Unfold m a b Source #
Build a stream by unfolding a monadic step function starting from a seed.
The step function returns the next element in the stream and the next seed
value. When it is done it returns Nothing and the stream ends.
Since: 0.8.0
unfoldr :: Applicative m => (a -> Maybe (b, a)) -> Unfold m a b Source #
Like unfoldrM but uses a pure step function.
>>>:{f [] = Nothing f (x:xs) = Just (x, xs) :}
>>>Unfold.fold Fold.toList (Unfold.unfoldr f) [1,2,3][1,2,3]
Since: 0.8.0
functionM :: Applicative m => (a -> m b) -> Unfold m a b Source #
Lift a monadic function into an unfold. The unfold generates a singleton stream.
Since: 0.8.0
function :: Applicative m => (a -> b) -> Unfold m a b Source #
Lift a pure function into an unfold. The unfold generates a singleton stream.
function f = functionM $ return . f
Since: 0.8.0
identity :: Applicative m => Unfold m a a Source #
Identity unfold. The unfold generates a singleton stream having the input as the only element.
identity = function Prelude.id
Pre-release
nilM :: Applicative m => (a -> m c) -> Unfold m a b Source #
Lift a monadic function into an unfold generating a nil stream with a side effect.
consM :: Applicative m => (a -> m b) -> Unfold m a b -> Unfold m a b Source #
Prepend a monadic single element generator function to an Unfold. The
same seed is used in the action as well as the unfold.
Pre-release
From Values
fromEffect :: Applicative m => m b -> Unfold m a b Source #
The unfold discards its input and generates a function stream using the supplied monadic action.
Pre-release
fromPure :: Applicative m => b -> Unfold m a b Source #
Discards the unfold input and always returns the argument of fromPure.
fromPure = fromEffect . pure
Pre-release
Generators
Generate a monadic stream from a seed.
repeatM :: Monad m => Unfold m (m a) a Source #
Generates an infinite stream repeating the seed.
Since: 0.8.0
replicateM :: Monad m => Int -> Unfold m (m a) a Source #
Generates a stream replicating the seed n times.
Since: 0.8.0
fromIndicesM :: Applicative m => (Int -> m a) -> Unfold m Int a Source #
fromIndicesM gen generates an infinite stream of values using gen
starting from the seed.
fromIndicesM f = Unfold.mapM f $ Unfold.enumerateFrom 0
Pre-release
iterateM :: Monad m => (a -> m a) -> Unfold m (m a) a Source #
Generates an infinite stream starting with the given seed and applying the given function repeatedly.
Since: 0.8.0
Enumerations
class Enum a => Enumerable a where Source #
Types that can be enumerated as a stream. The operations in this type
class are equivalent to those in the Enum type class, except that these
generate a stream instead of a list. Use the functions in
Streamly.Internal.Data.Unfold.Enumeration module to define new instances.
Pre-release
Methods
enumerateFrom :: Monad m => Unfold m a a Source #
Unfolds from generating a stream starting with the element
from, enumerating up to maxBound when the type is Bounded or
generating an infinite stream when the type is not Bounded.
>>>import qualified Streamly.Prelude as Stream>>>import qualified Streamly.Internal.Data.Unfold as Unfold
>>> Stream.toList $ Stream.take 4 $ Stream.unfold Unfold.enumerateFrom (0 :: Int) [0,1,2,3]
For Fractional types, enumeration is numerically stable. However, no
overflow or underflow checks are performed.
>>> Stream.toList $ Stream.take 4 $ Stream.unfold Unfold.enumerateFrom 1.1 [1.1,2.1,3.1,4.1]
Pre-release
enumerateFromTo :: Monad m => Unfold m (a, a) a Source #
Unfolds (from, to) generating a finite stream starting with the element
from, enumerating the type up to the value to. If to is smaller than
from then an empty stream is returned.
>>>import qualified Streamly.Prelude as Stream>>>import qualified Streamly.Internal.Data.Unfold as Unfold
>>> Stream.toList $ Stream.unfold Unfold.enumerateFromTo (0, 4) [0,1,2,3,4]
For Fractional types, the last element is equal to the specified to
value after rounding to the nearest integral value.
>>> Stream.toList $ Stream.unfold Unfold.enumerateFromTo (1.1, 4) [1.1,2.1,3.1,4.1] >>> Stream.toList $ Stream.unfold Unfold.enumerateFromTo (1.1, 4.6) [1.1,2.1,3.1,4.1,5.1]
Pre-release
enumerateFromThen :: Monad m => Unfold m (a, a) a Source #
Unfolds (from, then) generating a stream whose first element is
from and the successive elements are in increments of then. Enumeration
can occur downwards or upwards depending on whether then comes before or
after from. For Bounded types the stream ends when maxBound is
reached, for unbounded types it keeps enumerating infinitely.
>>>import qualified Streamly.Prelude as Stream>>>import qualified Streamly.Internal.Data.Unfold as Unfold
>>> Stream.toList $ Stream.take 4 $ Stream.unfold Unfold.enumerateFromThen (0, 2) [0,2,4,6] >>> Stream.toList $ Stream.take 4 $ Stream.unfold Unfold.enumerateFromThen (0,(-2)) [0,-2,-4,-6]
Pre-release
enumerateFromThenTo :: Monad m => Unfold m (a, a, a) a Source #
Unfolds (from, then, to) generating a finite stream whose first element
is from and the successive elements are in increments of then up to
to. Enumeration can occur downwards or upwards depending on whether then
comes before or after from.
>>>import qualified Streamly.Prelude as Stream>>>import qualified Streamly.Internal.Data.Unfold as Unfold
>>> Stream.toList $ Stream.unfold Unfold.enumerateFromThenTo (0, 2, 6) [0,2,4,6] >>> Stream.toList $ Stream.unfold Unfold.enumerateFromThenTo (0, (-2), (-6)) [0,-2,-4,-6]
Pre-release
Instances
Enumerate Num
enumerateFromNum :: (Monad m, Num a) => Unfold m a a Source #
Same as enumerateFromStepNum using a stride of 1:
>>> enumerateFromNum = lmap (from -> (from, 1)) Unfold.enumerateFromStepNum >>> Stream.toList $ Stream.take 6 $ Stream.unfold enumerateFromNum (0.9) [0.9,1.9,2.9,3.9,4.9,5.9]
Also, same as enumerateFromThenNum using a stride of 1 but see the note in
enumerateFromThenNum about the loss of precision:
>>> enumerateFromNum = lmap (from -> (from, from + 1)) Unfold.enumerateFromThenNum >>> Stream.toList $ Stream.take 6 $ Stream.unfold enumerateFromNum (0.9) [0.9,1.9,2.9,3.8999999999999995,4.8999999999999995,5.8999999999999995]
Internal
enumerateFromThenNum :: (Monad m, Num a) => Unfold m (a, a) a Source #
Same as 'enumerateFromStepNum (from, next)' using a stride of next - from:
>>> enumerateFromThenNum = lmap ((from, next) -> (from, next - from)) Unfold.enumerateFromStepNum
Example: @ >>> Stream.toList $ Stream.take 10 $ Stream.unfold enumerateFromThenNum (255::Word8,0) [255,0,1,2,3,4,5,6,7,8]
The implementation is numerically stable for floating point values.
Note that enumerateFromThenIntegral is faster for integrals.
Note that in the strange world of floating point numbers, using
enumerateFromThenNum (from, from + 1) is almost exactly the same as
enumerateFromStepNum (from, 1) but not precisely the same. Because (from +
1) - from is not exactly 1, it may lose some precision, the loss may also
be aggregated in each step, if you want that precision then use
enumerateFromStepNum instead.
Internal
enumerateFromStepNum :: (Monad m, Num a) => Unfold m (a, a) a Source #
Unfolds (from, stride) generating an infinite stream starting from
from and incrementing every time by stride. For Bounded types, after
the value overflows it keeps enumerating in a cycle:
>>> Stream.toList $ Stream.take 10 $ Stream.unfold Unfold.enumerateFromStepNum (255::Word8,1) [255,0,1,2,3,4,5,6,7,8]
The implementation is numerically stable for floating point values.
Note enumerateFromStepIntegral is faster for integrals.
Internal
Enumerating 'Bounded Integral Types
enumerateFromThenToIntegralBounded :: (Monad m, Integral a, Bounded a) => Unfold m (a, a, a) a Source #
Enumerating 'Unounded Integral' Types
Enumerating 'Small Integral' Types
enumerateFromSmallBounded :: (Monad m, Enum a, Bounded a) => Unfold m a a Source #
Enumerate from given starting Enum value from with stride of 1 till
maxBound
Internal
enumerateFromThenSmallBounded :: forall m a. (Monad m, Enum a, Bounded a) => Unfold m (a, a) a Source #
Enumerate from given starting Enum value from and next Enum value next
with stride of (fromEnum next - fromEnum from) till maxBound.
Internal
enumerateFromToSmall :: (Monad m, Enum a) => Unfold m (a, a) a Source #
Enumerate from given starting Enum value from and to Enum value to
with stride of 1 till to value.
Internal
enumerateFromThenToSmall :: (Monad m, Enum a) => Unfold m (a, a, a) a Source #
Enumerate from given starting Enum value from and then Enum value next
and to Enum value to with stride of (fromEnum next - fromEnum from)
till to value.
Internal
Enumerating Fractional Types
enumerateFromFractional :: (Monad m, Fractional a) => Unfold m a a Source #
enumerateFromThenFractional :: (Monad m, Fractional a) => Unfold m (a, a) a Source #
enumerateFromToFractional :: (Monad m, Fractional a, Ord a) => Unfold m (a, a) a Source #
Same as enumerateFromStepNum with a step of 1 and enumerating up to the
specified upper limit rounded to the nearest integral value:
>>> Stream.toList $ Stream.unfold Unfold.enumerateFromToFractional (0.1, 6.3) [0.1,1.1,2.1,3.1,4.1,5.1,6.1]
Internal
enumerateFromThenToFractional :: (Monad m, Fractional a, Ord a) => Unfold m (a, a, a) a Source #
From Containers
fromListM :: Monad m => Unfold m [m a] a Source #
Convert a list of monadic values to a Stream
Since: 0.8.0
fromStreamK :: Applicative m => Unfold m (Stream m a) a Source #
fromStreamD :: Applicative m => Unfold m (Stream m a) a Source #
Combinators
Mapping on Input
lmap :: (a -> c) -> Unfold m c b -> Unfold m a b Source #
Map a function on the input argument of the Unfold.
>>>u = Unfold.lmap (fmap (+1)) Unfold.fromList>>>Unfold.fold Fold.toList u [1..5][2,3,4,5,6]
lmap f = Unfold.many (Unfold.function f)
Since: 0.8.0
lmapM :: Monad m => (a -> m c) -> Unfold m c b -> Unfold m a b Source #
Map an action on the input argument of the Unfold.
lmapM f = Unfold.many (Unfold.functionM f)
Since: 0.8.0
supply :: a -> Unfold m a b -> Unfold m Void b Source #
Supply the seed to an unfold closing the input end of the unfold.
supply a = Unfold.lmap (Prelude.const a)
Pre-release
supplyFirst :: a -> Unfold m (a, b) c -> Unfold m b c Source #
Supply the first component of the tuple to an unfold that accepts a tuple as a seed resulting in a fold that accepts the second component of the tuple as a seed.
supplyFirst a = Unfold.lmap (a, )
Pre-release
supplySecond :: b -> Unfold m (a, b) c -> Unfold m a c Source #
Supply the second component of the tuple to an unfold that accepts a tuple as a seed resulting in a fold that accepts the first component of the tuple as a seed.
supplySecond b = Unfold.lmap (, b)
Pre-release
discardFirst :: Unfold m a b -> Unfold m (c, a) b Source #
Convert an Unfold into an unfold accepting a tuple as an argument,
using the argument of the original fold as the second element of tuple and
discarding the first element of the tuple.
discardFirst = Unfold.lmap snd
Pre-release
discardSecond :: Unfold m a b -> Unfold m (a, c) b Source #
Convert an Unfold into an unfold accepting a tuple as an argument,
using the argument of the original fold as the first element of tuple and
discarding the second element of the tuple.
discardSecond = Unfold.lmap fst
Pre-release
swap :: Unfold m (a, c) b -> Unfold m (c, a) b Source #
Convert an Unfold that accepts a tuple as an argument into an unfold
that accepts a tuple with elements swapped.
swap = Unfold.lmap Tuple.swap
Pre-release
Folding
Mapping on Output
map :: Functor m => (b -> c) -> Unfold m a b -> Unfold m a c Source #
Map a function on the output of the unfold (the type b).
Pre-release
mapM :: Monad m => (b -> m c) -> Unfold m a b -> Unfold m a c Source #
Apply a monadic function to each element of the stream and replace it with the output of the resulting action.
Since: 0.8.0
scanlM' :: Monad m => (b -> a -> m b) -> m b -> Unfold m c a -> Unfold m c b Source #
Scan the output of an Unfold to change it in a stateful manner.
Unimplemented
scan :: Monad m => Fold m b c -> Unfold m a b -> Unfold m a c Source #
Scan the output of an Unfold to change it in a stateful manner.
Pre-release
foldMany :: Fold m b c -> Unfold m a b -> Unfold m a c Source #
Apply a fold multiple times on the output of an unfold.
Unimplemented
Either Wrapped Input
either :: Applicative m => Unfold m a b -> Unfold m (Either a a) (Either b b) Source #
Make an unfold operate on values wrapped in an Either a a type. 'Right
a' translates to 'Right b' and 'Left a' translates to 'Left b'.
Internal
Filtering
takeWhileM :: Monad m => (b -> m Bool) -> Unfold m a b -> Unfold m a b Source #
Same as takeWhile but with a monadic predicate.
Since: 0.8.0
takeWhile :: Monad m => (b -> Bool) -> Unfold m a b -> Unfold m a b Source #
End the stream generated by the Unfold as soon as the predicate fails
on an element.
Since: 0.8.0
take :: Monad m => Int -> Unfold m a b -> Unfold m a b Source #
>>>u = Unfold.take 2 Unfold.fromList>>>Unfold.fold Fold.toList u [1..100][1,2]
Since: 0.8.0
filter :: Monad m => (b -> Bool) -> Unfold m a b -> Unfold m a b Source #
Include only those elements that pass a predicate.
Since: 0.8.0
filterM :: Monad m => (b -> m Bool) -> Unfold m a b -> Unfold m a b Source #
Same as filter but with a monadic predicate.
Since: 0.8.0
drop :: Monad m => Int -> Unfold m a b -> Unfold m a b Source #
drop n unf drops n elements from the stream generated by unf.
Since: 0.8.0
dropWhile :: Monad m => (b -> Bool) -> Unfold m a b -> Unfold m a b Source #
Similar to dropWhileM but with a pure condition function.
Since: 0.8.0
dropWhileM :: Monad m => (b -> m Bool) -> Unfold m a b -> Unfold m a b Source #
dropWhileM f unf drops elements from the stream generated by unf while
the condition holds true. The condition function f is monadic in nature.
Since: 0.8.0
Zipping
zipWithM :: Monad m => (b -> c -> m d) -> Unfold m a b -> Unfold m a c -> Unfold m a d Source #
Distribute the input to two unfolds and then zip the outputs to a single stream using a monadic zip function.
Stops as soon as any of the unfolds stops.
Pre-release
zipWith :: Monad m => (b -> c -> d) -> Unfold m a b -> Unfold m a c -> Unfold m a d Source #
Like zipWithM but with a pure zip function.
>>>square = fmap (\x -> x * x) Unfold.fromList>>>cube = fmap (\x -> x * x * x) Unfold.fromList>>>u = Unfold.zipWith (,) square cube>>>Unfold.fold Fold.toList u [1..5][(1,1),(4,8),(9,27),(16,64),(25,125)]
zipWith f = zipWithM (\a b -> return $ f a b)
Since: 0.8.0
Cross product
crossWithM :: Monad m => (b -> c -> m d) -> Unfold m a b -> Unfold m a c -> Unfold m a d Source #
Create a cross product (vector product or cartesian product) of the output streams of two unfolds using a monadic combining function.
Pre-release
crossWith :: Monad m => (b -> c -> d) -> Unfold m a b -> Unfold m a c -> Unfold m a d Source #
Like crossWithM but uses a pure combining function.
crossWith f = crossWithM (\b c -> return $ f b c)
>>>u1 = Unfold.lmap fst Unfold.fromList>>>u2 = Unfold.lmap snd Unfold.fromList>>>u = Unfold.crossWith (,) u1 u2>>>Unfold.fold Fold.toList u ([1,2,3], [4,5,6])[(1,4),(1,5),(1,6),(2,4),(2,5),(2,6),(3,4),(3,5),(3,6)]
Since: 0.8.0
cross :: Monad m => Unfold m a b -> Unfold m a c -> Unfold m a (b, c) Source #
See crossWith.
cross = crossWith (,)
To cross the streams from a tuple we can write:
crossProduct :: Monad m => Unfold m a b -> Unfold m c d -> Unfold m (a, c) (b, d) crossProduct u1 u2 = cross (lmap fst u1) (lmap snd u2)
Pre-release
Nesting
data ConcatState s1 s2 Source #
Constructors
| ConcatOuter s1 | |
| ConcatInner s1 s2 |
many :: Monad m => Unfold m a b -> Unfold m b c -> Unfold m a c Source #
Apply the second unfold to each output element of the first unfold and flatten the output in a single stream.
Since: 0.8.0
concatMapM :: Monad m => (b -> m (Unfold m a c)) -> Unfold m a b -> Unfold m a c Source #
Map an unfold generating action to each element of an unfold and flatten the results into a single stream.
Resource Management
Arguments
| :: Monad m | |
| => (a -> m c) | before |
| -> (forall s. m s -> m (Either e s)) | try (exception handling) |
| -> (c -> m d) | after, on normal stop |
| -> Unfold m (c, e) b | on exception |
| -> Unfold m c b | unfold to run |
| -> Unfold m a b |
Like gbracket but with following differences:
- alloc action
a -> m cruns with async exceptions enabled - cleanup action
c -> m dwon't run if the stream is garbage collected after partial evaluation. - does not require a
MonadAsyncconstraint.
Inhibits stream fusion
Pre-release
Arguments
| :: MonadRunInIO m | |
| => (a -> m c) | before |
| -> (forall s. m s -> m (Either e s)) | try (exception handling) |
| -> (c -> m d) | after, on normal stop, or GC |
| -> Unfold m (c, e) b | on exception |
| -> Unfold m c b | unfold to run |
| -> Unfold m a b |
Run the alloc action a -> m c with async exceptions disabled but keeping
blocking operations interruptible (see mask). Use the
output c as input to Unfold m c b to generate an output stream. When
unfolding use the supplied try operation forall s. m s -> m (Either e s)
to catch synchronous exceptions. If an exception occurs run the exception
handling unfold Unfold m (c, e) b.
The cleanup action c -> m d, runs whenever the stream ends normally, due
to a sync or async exception or if it gets garbage collected after a partial
lazy evaluation. See bracket for the semantics of the cleanup action.
gbracket can express all other exception handling combinators.
Inhibits stream fusion
Pre-release
before :: (a -> m c) -> Unfold m a b -> Unfold m a b Source #
Run a side effect a -> m c on the input a before unfolding it using
Unfold m a b.
before f = lmapM (\a -> f a >> return a)
Pre-release
after_ :: Monad m => (a -> m c) -> Unfold m a b -> Unfold m a b Source #
Like after with following differences:
- action
a -> m cwon't run if the stream is garbage collected after partial evaluation. - Monad
mdoes not require any other constraints.
Pre-release
finally :: (MonadAsync m, MonadCatch m) => (a -> m c) -> Unfold m a b -> Unfold m a b Source #
Unfold the input a using Unfold m a b, run an action on a whenever
the unfold stops normally, aborts due to an exception or if it is garbage
collected after a partial lazy evaluation.
The semantics of the action a -> m c are similar to the cleanup action
semantics in bracket.
finally release = bracket return release
See also finally_
Inhibits stream fusion
Pre-release
finally_ :: MonadCatch m => (a -> m c) -> Unfold m a b -> Unfold m a b Source #
Like finally with following differences:
- action
a -> m cwon't run if the stream is garbage collected after partial evaluation. - does not require a
MonadAsyncconstraint.
Inhibits stream fusion
Pre-release
bracket :: (MonadAsync m, MonadCatch m) => (a -> m c) -> (c -> m d) -> Unfold m c b -> Unfold m a b Source #
Run the alloc action a -> m c with async exceptions disabled but keeping
blocking operations interruptible (see mask). Use the
output c as input to Unfold m c b to generate an output stream.
c is usually a resource under the state of monad m, e.g. a file
handle, that requires a cleanup after use. The cleanup action c -> m d,
runs whenever the stream ends normally, due to a sync or async exception or
if it gets garbage collected after a partial lazy evaluation.
bracket only guarantees that the cleanup action runs, and it runs with
async exceptions enabled. The action must ensure that it can successfully
cleanup the resource in the face of sync or async exceptions.
When the stream ends normally or on a sync exception, cleanup action runs immediately in the current thread context, whereas in other cases it runs in the GC context, therefore, cleanup may be delayed until the GC gets to run.
Inhibits stream fusion
Pre-release
bracket_ :: MonadCatch m => (a -> m c) -> (c -> m d) -> Unfold m c b -> Unfold m a b Source #
Like bracket but with following differences:
- alloc action
a -> m cruns with async exceptions enabled - cleanup action
c -> m dwon't run if the stream is garbage collected after partial evaluation. - does not require a
MonadAsyncconstraint.
Inhibits stream fusion
Pre-release
Exceptions
onException :: MonadCatch m => (a -> m c) -> Unfold m a b -> Unfold m a b Source #
Unfold the input a using Unfold m a b, run the action a -> m c on
a if the unfold aborts due to an exception.
Inhibits stream fusion
Pre-release