Storage.Hashed.Monad

An experimental monadic interface to Tree mutation. The main idea is to simulate IO-ish manipulation of real filesystem (that's the state part of the monad), and to keep memory usage down by reasonably often dumping the intermediate data to disk and forgetting it. The monad interface itself is generic, and a number of actual implementations can be used. This module provides just virtualTreeIO that never writes any changes, but may trigger filesystem reads as appropriate.

Documentation

virtualTreeIO :: TreeIO a -> Tree IO -> IO (a, Tree IO)

virtualTreeMonad :: Monad m => TreeMonad m a -> Tree m -> m (a, Tree m)

Run a TreeIO action without storing any changes. This is useful for running monadic tree mutations for obtaining the resulting Tree (as opposed to their effect of writing a modified tree to disk). The actions can do both read and write -- reads are passed through to the actual filesystem, but the writes are held in memory in a form of modified Tree.

readFile :: (TreeRO m, MonadError e m) => AnchoredPath -> m ByteString

Grab content of a file in the current Tree at the given path.

writeFile :: (TreeRW m, MonadError e m) => AnchoredPath -> ByteString -> m ()

Change content of a file at a given path. The change will be eventually flushed to disk, but might be buffered for some time.

createDirectory :: (TreeRW m, MonadError e m) => AnchoredPath -> m ()

rename :: (TreeRW m, MonadError e m) => AnchoredPath -> AnchoredPath -> m ()

unlink :: (TreeRW m, MonadError e m) => AnchoredPath -> m ()

fileExists :: (TreeRO m, MonadError e m) => AnchoredPath -> m Bool

Check for existence of a file.

directoryExists :: (TreeRO m, MonadError e m) => AnchoredPath -> m Bool

Check for existence of a directory.

exists :: (TreeRO m, MonadError e m) => AnchoredPath -> m Bool

Check for existence of a node (file or directory, doesn't matter).

withDirectory :: (TreeRO m, MonadError e m) => AnchoredPath -> m a -> m a

currentDirectory :: TreeRO m => m AnchoredPath

tree :: TreeState m -> Tree m

data TreeState m

Internal state of the TreeIO monad. Keeps track of the current Tree content, unsync'd changes and a current working directory (of the monad).

type TreeMonad m = RWST AnchoredPath () (TreeState m) m

A TreeIO monad. A sort of like IO but it keeps a TreeState around as well, which is a sort of virtual filesystem. Depending on how you obtained your TreeIO, the actions in your virtual filesystem get somehow reflected in the actual real filesystem. For virtualTreeIO, nothing happens in real filesystem, however with plainTreeIO, the plain tree will be updated every now and then, and with hashedTreeIO a darcs-style hashed tree will get updated.

type TreeIO = TreeMonad IO

runTreeMonad :: Monad m => TreeMonad m a -> TreeState m -> m (a, Tree m)

type PathSet = Set AnchoredPath

initialState :: Tree m -> (PathSet -> TreeMonad m ()) -> TreeState m

replaceItem :: (MonadError e m, Functor m, Monad m) => AnchoredPath -> Maybe (TreeItem m) -> TreeMonad m ()

Replace an item with a new version without modifying the content of the tree. This does not do any change tracking. Ought to be only used from a sync implementation for a particular storage format. The presumed use-case is that an existing in-memory Blob is replaced with a one referring to an on-disk file.