Data.Knob

Create memory‐backed Handles, referencing virtual files. This is mostly useful for testing Handle‐based APIs without having to interact with the filesystem.

import Data.ByteString (pack)
import Data.Knob
import System.IO

main = do
    knob <- newKnob (pack [])
    h <- newFileHandle knob "test.txt" WriteMode
    hPutStrLn h "Hello world!"
    hClose h
    bytes <- Data.Knob.getContents knob
    putStrLn ("Wrote bytes: " ++ show bytes)

Documentation

data Knob

A knob is a basic virtual file, which contains a byte buffer. A knob can have multiple Handles open to it, each of which behaves like a standard file handle.

Use getContents and setContents to inspect and modify the knob's byte buffer.

newKnob :: MonadIO m => ByteString -> m Knob

getContents :: MonadIO m => Knob -> m ByteString

setContents :: MonadIO m => Knob -> ByteString -> m ()

newFileHandle

Arguments

:: MonadIO m

=> Knob

-> String

Filename shown in error messages

-> IOMode

-> m Handle

Create a new Handle pointing to a Knob. This handle behaves like a file-backed handle for most purposes.

withFileHandle

Arguments

:: MonadIO m

=> Knob

-> String

Filename shown in error messages.

-> IOMode

-> (Handle -> IO a)

-> m a

See newFileHandle.