Pipes.Group

Element-agnostic grouping utilities for pipes

See Pipes.Group.Tutorial for an extended tutorial

Lenses

groupsBy :: Monad m => (a' -> a' -> Bool) -> Lens (Producer a' m x) (Producer a m x) (FreeT (Producer a' m) m x) (FreeT (Producer a m) m x)

groupsBy splits a Producer into a FreeT of Producers grouped using the given equality predicate

>>> P.toList . intercalates (P.yield '|') . view (groupsBy (==)) $ P.each "12233345"
"1|22|333|4|5"

You can think of this as:

groupsBy
    :: Monad m
    => (a -> a -> Bool) -> Lens' (Producer a m x) (FreeT (Producer a m) m x)

groups :: (Monad m, Eq a') => Lens (Producer a' m x) (Producer a m x) (FreeT (Producer a' m) m x) (FreeT (Producer a m) m x)

Like groupsBy, where the equality predicate is (==)

>>> P.toList . intercalates (P.yield '|') . view groups $ P.each "12233345"
"1|22|333|4|5"

You can think of this as:

groups
    :: (Monad m, Eq a) => Lens' (Producer a m x) (FreeT (Producer a m) m x)

chunksOf :: Monad m => Int -> Lens (Producer a' m x) (Producer a m x) (FreeT (Producer a' m) m x) (FreeT (Producer a m) m x)

chunksOf is an splits a Producer into a FreeT of Producers of fixed length

>>> P.toList . intercalates (P.yield '|') . view (chunksOf 3) $ P.each "12233345"
"122|333|45"

You can think of this as:

chunksOf
    :: Monad m => Int -> Lens' (Producer a m x) (FreeT (Producer a m) m x)

Transformations

takes :: (Functor f, Monad m) => Int -> FreeT f m () -> FreeT f m ()

(takes n) only keeps the first n functor layers of a FreeT

>>> P.toList . intercalates (P.yield '|') . takes 3 . view groups $ P.each "12233345"
"1|22|333"

You can think of this as:

takes
    :: (Functor f, Monad m)
    => Int -> FreeT (Producer a m) m () -> FreeT (Producer a m) m ()

takes' :: Monad m => Int -> FreeT (Producer a m) m x -> FreeT (Producer a m) m x

(takes' n) only keeps the first n Producers of a FreeT

takes' differs from takes by draining unused Producers in order to preserve the return value. This makes it a suitable argument for maps.

drops :: Monad m => Int -> FreeT (Producer a m) m x -> FreeT (Producer a m) m x

(drops n) peels off the first n Producer layers of a FreeT

>>> P.toList . intercalates (P.yield '|') . drops 3 . view groups $ P.each "12233345"
"4|5"

Use carefully: the peeling off is not free. This runs the first n layers, just discarding everything they produce.

maps :: (Monad m, Functor g) => (forall r. f r -> g r) -> FreeT f m x -> FreeT g m x

Transform each individual functor layer of a FreeT

You can think of this as:

maps
    :: (forall r . Producer a m r -> Producer b m r)
    -> FreeT (Producer a m) m x -> FreeT (Producer b m) m x

This is just a synonym for transFreeT

individually :: (Monad m, Functor g) => Setter (FreeT f m x) (FreeT g m x) (f (FreeT f m x)) (g (FreeT f m x))

Lens to transform each individual functor layer of a FreeT

over individually = maps  -- ... with a less general type

Joiners

concats :: Monad m => FreeT (Producer a m) m x -> Producer a m x

Join a FreeT-delimited stream of Producers into a single Producer

intercalates :: Monad m => Producer a m () -> FreeT (Producer a m) m x -> Producer a m x

Join a FreeT-delimited stream of Producers into a single Producer by intercalating a Producer in between them

Folds

These folds are designed to be compatible with the foldl library. See the purely and impurely functions from that library for more details.

For example, to count the number of Producer layers in a FreeT, you can write:

 import Control.Applicative (pure)
 import qualified Control.Foldl as L
 import Pipes.Group
 import qualified Pipes.Prelude as P

 count :: Monad m => FreeT (Producer a m) m () -> m Int
 count = P.sum . L.purely folds (pure 1)

folds

Arguments

:: Monad m

=> (x -> a -> x)

Step function

-> x

Initial accumulator

-> (x -> b)

Extraction function

-> FreeT (Producer a m) m r

-> Producer b m r

Fold each Producer of a FreeT

purely folds
    :: Monad m => Fold a b -> FreeT (Producer a m) m r -> Producer b m r

foldsM

Arguments

:: Monad m

=> (x -> a -> m x)

Step function

-> m x

Initial accumulator

-> (x -> m b)

Extraction function

-> FreeT (Producer a m) m r

-> Producer b m r

Fold each Producer of a FreeT, monadically

impurely foldsM
    :: Monad m => FoldM a b -> FreeT (Producer a m) m r -> Producer b m r

Re-exports

Control.Monad.Trans.Class re-exports lift.

Control.Monad.Trans.Free re-exports FreeF and FreeT

Pipes re-exports Producer, yield, and next.

module Control.Monad.Trans.Class

module Control.Monad.Trans.Free

module Pipes