# streams: Various Haskell 2010 stream comonads

Various Haskell 2010 stream comonads.

Data.Stream.Branching provides an "f-Branching Stream" comonad, aka the cofree comonad, or generalized rose tree.

data Stream f a = a :< f (Stream a)

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.

data Future a = Last a | a :< Future a

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.

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`

data NonEmpty a = a :| [a]

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.

data Stream a = a :< Stream a

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.

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.

data Zipper a = !Integer :~ (Integer -> a)

Data.Stream.Supply provides a comonadic supply of unique values, which are generated impurely as the tree is explored.

*Changes since 0.5*:
* Data.Stream.Supply added
*Changes since 0.1*:

A number of strictness issues with

`NonEmpty`

were fixedMore documentation

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Versions | 0.1.1, 0.2, 0.3, 0.3.1, 0.4, 0.5.0, 0.5.1, 0.5.1.1, 0.5.1.2, 0.6.0, 0.6.0.1, 0.6.1.1, 0.6.1.2, 0.6.3, 0.7.0, 0.7.1, 0.7.2, 0.8.0, 0.8.0.1, 0.8.0.2, 0.8.0.3, 0.8.0.4, 0.8.1, 0.8.2, 3.0, 3.0.0.1, 3.0.1, 3.0.1.1, 3.1, 3.1.1, 3.2, 3.2.1, 3.3 |
---|---|

Dependencies | base (>=4 && <4.4), comonad (==0.9.*), distributive (==0.1.*), functor-apply (==0.10.*), semigroups (>=0.3.4 && <0.4) [details] |

License | BSD-3-Clause |

Copyright | Copyright 2011 Edward Kmett Copyright 2010 Tony Morris, Oliver Taylor, Eelis van der Weegen Copyright 2007-2010 Wouter Swierstra, Bas van Dijk |

Author | Edward A. Kmett |

Maintainer | Edward A. Kmett <ekmett@gmail.com> |

Category | Control, Comonads |

Home page | http://github.com/ekmett/streams |

Source repo | head: git clone git://github.com/ekmett/streams.git |

Uploaded | by EdwardKmett at Sat Jan 29 11:41:29 UTC 2011 |

Distributions | LTSHaskell:3.3, NixOS:3.3, Stackage:3.3, openSUSE:3.3 |

Downloads | 12064 total (60 in the last 30 days) |

Rating | 2.0 (votes: 1) [estimated by rule of succession] |

Your Rating | |

Status | Docs uploaded by user Build status unknown [no reports yet] Hackage Matrix CI |

## Modules

[Index]

## Downloads

- streams-0.5.1.tar.gz [browse] (Cabal source package)
- Package description (as included in the package)