darcs-2.18.3: a distributed, interactive, smart revision control system
Safe HaskellSafe-Inferred
LanguageHaskell2010

Darcs.Util.Tree.Monad

Description

A monad transformer for 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 implementation is configured by passing a procedure of type DumpItem to runTreeMonad.

This module provides the pre-configured virtualTreeIO that never writes any changes, but may trigger filesystem reads as appropriate.

Synopsis

TreeMonad

type TreeMonad m = RWST (DumpItem m) () (TreeState m) m Source #

A monad transformer that adds state of type TreeState and an environment of type DumpItem.

runTreeMonad :: Monad m => TreeMonad m a -> Tree m -> DumpItem m -> m (a, Tree m) Source #

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

Run a TreeMonad 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 the form of a modified Tree.

Specializing to IO

type TreeIO = TreeMonad IO Source #

TreeMonad specialized to IO

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

virtualTreeMonad specialized to IO

Read actions

readFile :: MonadThrow m => AnchoredPath -> TreeMonad m ByteString Source #

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

exists :: MonadThrow m => AnchoredPath -> TreeMonad m Bool Source #

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

directoryExists :: Monad m => AnchoredPath -> TreeMonad m Bool Source #

Check for existence of a directory.

fileExists :: Monad m => AnchoredPath -> TreeMonad m Bool Source #

Check for existence of a file.

Write actions

writeFile :: MonadThrow m => AnchoredPath -> ByteString -> TreeMonad m () Source #

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 :: Monad m => AnchoredPath -> TreeMonad m () Source #

Create a directory.

unlink :: Monad m => AnchoredPath -> TreeMonad m () Source #

Remove the item at a path.

rename :: MonadThrow m => AnchoredPath -> AnchoredPath -> TreeMonad m () Source #

Rename the item at a path.

copy :: MonadThrow m => AnchoredPath -> AnchoredPath -> TreeMonad m () Source #

Copy an item from some path to another path. Doing this with a SubTree is weird... it means copy recursively, but with lazy copy-on-write semantics. What happens when we flush that? Seems to work, though, as it is used in Darcs.UI.Commands.Convert.Import

Other actions

findM :: Monad m => Tree m -> AnchoredPath -> m (Maybe (TreeItem m)) Source #

findFileM :: Monad m => Tree m -> AnchoredPath -> m (Maybe (Blob m)) Source #

findTreeM :: Monad m => Tree m -> AnchoredPath -> m (Maybe (Tree m)) Source #