| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
System.IO.Resource.Linear
Description
This module defines an IO monad for linearly working with system resources like files. It provides tools to take resources that are currently unsafely accessible from System.IO and use them in this monad.
Import this module qualified to avoid name clashes.
To use this RIO monad, create some RIO computation,
run it to get a System.IO computation.
A simple example
>>>:set -XLinearTypes>>>:set -XQualifiedDo>>>:set -XNoImplicitPrelude>>>import qualified System.IO.Resource.Linear as Linear>>>import qualified Control.Functor.Linear as Control>>>import qualified Data.Text as Text>>>import Prelude.Linear>>>import qualified Prelude>>>:{linearWriteToFile :: IO () linearWriteToFile = Linear.run $ Control.do handle1 <- Linear.openFile "/home/user/test.txt" Linear.WriteMode handle2 <- Linear.hPutStrLn handle1 (Text.pack "hello there") () <- Linear.hClose handle2 Control.return (Ur ()) :}
To enable do notation, QualifiedDo extension is used. But since QualifiedDo
only modifies the desugaring of binds, we still need to qualify return.
Synopsis
- data RIO a
- run :: RIO (Ur a) -> IO a
- type Handle = Resource Handle
- openFile :: FilePath -> IOMode -> RIO Handle
- openBinaryFile :: FilePath -> IOMode -> RIO Handle
- data IOMode
- hClose :: Handle %1 -> RIO ()
- hIsEOF :: Handle %1 -> RIO (Ur Bool, Handle)
- hGetChar :: Handle %1 -> RIO (Ur Char, Handle)
- hPutChar :: Handle %1 -> Char -> RIO Handle
- hGetLine :: Handle %1 -> RIO (Ur Text, Handle)
- hPutStr :: Handle %1 -> Text -> RIO Handle
- hPutStrLn :: Handle %1 -> Text -> RIO Handle
- hSeek :: Handle %1 -> SeekMode -> Integer -> RIO Handle
- data SeekMode
- hTell :: Handle %1 -> RIO (Ur Integer, Handle)
- data Resource a
- release :: Resource a %1 -> RIO ()
- unsafeAcquire :: IO (Ur a) -> (a -> IO ()) -> RIO (Resource a)
- unsafeFromSystemIOResource :: (a -> IO b) -> Resource a %1 -> RIO (Ur b, Resource a)
- unsafeFromSystemIOResource_ :: (a -> IO ()) -> Resource a %1 -> RIO (Resource a)
- type UnsafeResource = Resource
- unsafeRelease :: Resource a %1 -> RIO ()
The Resource I/O Monad
The resource-aware I/O monad. This monad guarantees that acquired resources are always released.
run :: RIO (Ur a) -> IO a Source #
Take a RIO computation with a value a that is not linearly bound and
make it a System.IO computation.
Using Resource Handles
File I/O
openBinaryFile :: FilePath -> IOMode -> RIO Handle Source #
See System.IO.openBinaryFile
Since: 0.3.0
See openFile
Constructors
| ReadMode | |
| WriteMode | |
| AppendMode | |
| ReadWriteMode |
Working with Handles
A mode that determines the effect of hSeek hdl mode i.
Constructors
| AbsoluteSeek | the position of |
| RelativeSeek | the position of |
| SeekFromEnd | the position of |
Instances
| Enum SeekMode | Since: base-4.2.0.0 |
| Ix SeekMode | Since: base-4.2.0.0 |
Defined in GHC.IO.Device Methods range :: (SeekMode, SeekMode) -> [SeekMode] # index :: (SeekMode, SeekMode) -> SeekMode -> Int # unsafeIndex :: (SeekMode, SeekMode) -> SeekMode -> Int # inRange :: (SeekMode, SeekMode) -> SeekMode -> Bool # rangeSize :: (SeekMode, SeekMode) -> Int # unsafeRangeSize :: (SeekMode, SeekMode) -> Int # | |
| Read SeekMode | Since: base-4.2.0.0 |
| Show SeekMode | Since: base-4.2.0.0 |
| Eq SeekMode | Since: base-4.2.0.0 |
| Ord SeekMode | Since: base-4.2.0.0 |
Defined in GHC.IO.Device | |
Creating new types of resources
The type of system resources. To create and use resources, you need to use the API since the constructor is not released.
release :: Resource a %1 -> RIO () Source #
release rr was acquired.
unsafeAcquire :: IO (Ur a) -> (a -> IO ()) -> RIO (Resource a) Source #
Given a resource in the System.IO.Linear.IO monad, and
given a function to release that resource, provides that resource in
the RIO monad. For example, releasing a Handle from System.IO
would be done with fromSystemIO hClose. Because this release function
is an input, and could be wrong, this function is unsafe.
unsafeFromSystemIOResource :: (a -> IO b) -> Resource a %1 -> RIO (Ur b, Resource a) Source #
Given a System.IO computation on an unsafe resource,
lift it to RIO computaton on the acquired resource.
That is function of type a -> IO b turns into a function of type
Resource a %1-> RIO (Ur b)
along with threading the Resource a.
unsafeFromSystemIOResource is only safe to use on actions which do not release
the resource.
Note that the result b can be used non-linearly.
unsafeFromSystemIOResource_ :: (a -> IO ()) -> Resource a %1 -> RIO (Resource a) Source #
Specialised variant of unsafeFromSystemIOResource for actions that don't
return a value.
Deprecated symbols
type UnsafeResource = Resource Source #
Deprecated: UnsafeResource has been renamed to Resource
Deprecated alias for Resource