# streaming-bracketed

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## What's this?

A resource management "decorator" for the `Stream` type from
[streaming](http://hackage.haskell.org/package/streaming).  

The idea is that the `Bracketed` type represents a `Stream` which might have
some finalizers that will be triggered when we reach a given point in the
stream.

By being careful about how we lift operations to work on `Bracketed` streams,
we can ensure that finalizers are promptly called even with operations like
`take`.

`Bracketed` streams are ultimately consumed by using a continuation.

## Differences with resourcet

[resourcet](http://hackage.haskell.org/package/resourcet) is a widely used
library for resource handling. It provides a monad transformer over IO that
keeps track of registered resources and ensures proper cleanup.

The main differences with the present library are:

- This library only works on `Stream`s from streaming.

- `Bracketed` sits above the streaming monad, not below like `ResourceT`.

- This library aims to provide smarter handling of stream functions like
  `take`, without too much hassle.

- In this library finalizer scopes are nested, unlike `ResourceT` which allows
  arbitrary interleavings. 

## Doubts

- Lifting functions like `splitAt` might cause problems if we try to use the
  rest of the stream.

## Motivation

From the
[CHANGELOG](http://hackage.haskell.org/package/streaming-0.2.1.0/changelog) of
the [streaming](http://hackage.haskell.org/package/streaming) package:

    Remove bracketStream, MonadCatch instance, and everything dealing with
    ResourceT. All of these things of sort of broken for Stream since there is no
    guarantee of linear consumption (functions like take can prevent finalizers
    from running).

[One Github issue](https://github.com/haskell-streaming/streaming/issues/52).

[Another one](https://github.com/haskell-streaming/streaming-with/issues/2).

[Streaming libs exercise/challenge](https://twitter.com/DiazCarrete/status/1016073374458671104):

    Given a list [(Filepath,Int,Int)] of files and line ranges, create a stream
    of lines belonging to the concatenated ranges.

    Prompt release of file handles is required. resource-handling monads and
    "withXXX"-style functions are allowed.