name: streams
category: Control, Comonads
version: 0.3
license: BSD3
cabal-version: >= 1.6
license-file: LICENSE
author: Edward A. Kmett
maintainer: Edward A. Kmett
stability: provisional
homepage: http://github.com/ekmett/streams
copyright: Copyright 2011 Edward Kmett
Copyright 2010 Tony Morris, Oliver Taylor, Eelis van der Weegen
Copyright 2007-2010 Wouter Swierstra, Bas van Dijk
synopsis: Various Haskell 2010 stream comonads
build-type: Simple
extra-source-files: README
description:
Various Haskell 2010 stream comonads.
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* "Data.Stream.Branching" provides an \"f-Branching Stream\" comonad, aka the cofree comonad, or generalized rose tree.
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> data Stream f a = a :< f (Stream a)
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* "Data.Stream.Future" provides a coinductive anti-causal stream, or non-empty 'ZipList'. The comonad provides access to only the
tail of the stream. Like a conventional 'ZipList', this is /not/ a monad.
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> data Future a = Last a | a :< Future a
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* "Data.Stream.Future.Skew" provides a non-empty skew-binary random-access-list with the semantics of @Data.Stream.Future@. As with
"Data.Stream.Future" this stream is not a 'Monad', since the 'Applicative' instance zips streams of potentially differing lengths.
The random-access-list structure provides a number of operations logarithmic access time, but makes 'Data.Stream.Future.Skew.cons'
less productive. Where applicable "Data.Stream.Infinite.Skew" may be more efficient, due to a lazier and more efficient 'Applicative'
instance.
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>
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* "Data.Stream.NonEmpty" provides a non-empty list comonad where the Applicative and Monad work like those of the @[a]@.
Being non-empty, it trades in the 'Alternative' and 'Monoid' instances of @[a]@ for weaker append-based 'FunctorAlt' and 'Semigroup'
instances while becoming a member of 'Comonad' and 'ComonadApply'. Acting like a list, the semantics of '<*>' and
'<.>' take a cross-product of membership from both 'NonEmpty' lists rather than zipping like a 'Future'
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> data NonEmpty a = a :| [a]
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* "Data.Stream.Infinite" provides a coinductive infinite anti-causal stream. The 'Comonad' provides access to the tail of the
stream and the 'Applicative' zips streams together. Unlike 'Future', infinite stream form a 'Monad'. The monad diagonalizes
the 'Stream', which is consistent with the behavior of the 'Applicative', and the view of a 'Stream' as a isomorphic to the reader
monad from the natural numbers. Being infinite in length, there is no 'Alternative' instance, but instead the 'FunctorAlt'
instance provides access to the 'Semigroup' of interleaving streams.
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> data Stream a = a :< Stream a
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* "Data.Stream.Infinite.Skew" provides an infinite skew-binary random-access-list with the semantics of "Data.Stream.Infinite"
Since every stream is infinite, the 'Applicative' instance can be considerably less strict than the corresponding instance for
"Data.Stream.Future.Skew" and performs asymptotically better.
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>
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* "Data.Stream.Infinite.Functional.Zipper" provides a bi-infinite sequence, represented as a pure function with an accumulating
parameter added to optimize moving the current focus.
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> data Zipper a = !Integer :~ (Integer -> a)
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/Changes since 0.1/:
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* A number of strictness issues with 'NonEmpty' were fixed
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* More documentation
source-repository head
type: git
location: git://github.com/ekmett/streams.git
library
build-depends:
base >= 4 && < 4.4,
comonad >= 0.6.2.1 && < 0.7,
functor-apply >= 0.7.4 && < 0.8,
semigroups >= 0.3.2 && < 0.4
extensions: CPP
if impl(ghc)
cpp-options: -DLANGUAGE_DeriveDataTypeable
extensions: FlexibleContexts, DeriveDataTypeable
exposed-modules:
Data.Stream.Branching
Data.Stream.Future
Data.Stream.Future.Skew
Data.Stream.NonEmpty
Data.Stream.Infinite
Data.Stream.Infinite.Skew
Data.Stream.Infinite.Functional.Zipper
ghc-options: -Wall