streams (hackage): Various Haskell 2010 stream comonads. * 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.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.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.  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.Stream.Supply provides a comonadic supply of unique values, which are generated impurely as the tree is explored.
Keywords: bsd3|comonads|control|library