Storage.Hashed.Tree

The abstract representation of a Tree and useful abstract utilities to handle those.

Documentation

data Tree m

Abstraction of a filesystem tree. Please note that the Tree returned by the respective read operations will have TreeStub items in it. To obtain a Tree without such stubs, call expand on it, eg.:

 tree <- readDarcsPristine "." >>= expand

When a Tree is expanded, it becomes "final". All stubs are forced and the Tree can be traversed purely. Access to actual file contents stays in IO though.

A Tree may have a Hash associated with it. A pair of Tree's is identical whenever their hashes are (the reverse need not hold, since not all Trees come equipped with a hash).

Instances

Monad m => FilterTree Tree m

data Blob m

Constructors

Blob !(m ByteString) !Hash

data TreeItem m

Constructors

File !(Blob m)

SubTree !(Tree m)

Stub !(m (Tree m)) !Hash

data ItemType

Constructors

BlobType

TreeType

Instances

Eq ItemType

Show ItemType

data Hash

Constructors

SHA256 !ByteString

SHA1 !ByteString

NoHash

Instances

Eq Hash

Ord Hash

Read Hash

Show Hash

makeTree :: Monad m => [(Name, TreeItem m)] -> Tree m

makeTreeWithHash :: Monad m => [(Name, TreeItem m)] -> Hash -> Tree m

emptyTree :: Monad m => Tree m

emptyBlob :: Monad m => Blob m

makeBlob :: Monad m => ByteString -> Blob m

makeBlobBS :: Monad m => ByteString -> Blob m

Unfolding stubbed (lazy) Trees.

By default, Tree obtained by a read function is stubbed: it will contain Stub items that need to be executed in order to access the respective subtrees. expand will produce an unstubbed Tree.

expandUpdate :: Monad m => (AnchoredPath -> Tree m -> m (Tree m)) -> Tree m -> m (Tree m)

expand :: Monad m => Tree m -> m (Tree m)

Expand a stubbed Tree into a one with no stubs in it. You might want to filter the tree before expanding to save IO. This is the basic implementation, which may be overriden by some Tree instances (this is especially true of the Index case).

expandPath :: Monad m => Tree m -> AnchoredPath -> m (Tree m)

Unfold a path in a (stubbed) Tree, such that the leaf node of the path is reachable without crossing any stubs. Moreover, the leaf ought not be a Stub in the resulting Tree. A non-existent path is expanded as far as it can be.

Tree access and lookup.

items :: Tree m -> Map Name (TreeItem m)

list :: Tree m -> [(AnchoredPath, TreeItem m)]

List all contents of a Tree.

listImmediate :: Tree m -> [(Name, TreeItem m)]

treeHash :: Tree m -> Hash

Get hash of a Tree. This is guaranteed to uniquely identify the Tree (including any blob content), as far as cryptographic hashes are concerned. Sha256 is recommended.

lookup :: Tree m -> Name -> Maybe (TreeItem m)

Look up a Tree item (an immediate subtree or blob).

find :: Tree m -> AnchoredPath -> Maybe (TreeItem m)

Find a TreeItem by its path. Gives Nothing if the path is invalid.

findFile :: Tree m -> AnchoredPath -> Maybe (Blob m)

Find a Blob by its path. Gives Nothing if the path is invalid, or does not point to a Blob.

findTree :: Tree m -> AnchoredPath -> Maybe (Tree m)

Find a Tree by its path. Gives Nothing if the path is invalid, or does not point to a Tree.

itemHash :: TreeItem m -> Hash

Get a hash of a TreeItem. May be Nothing.

itemType :: TreeItem m -> ItemType

zipCommonFiles :: (AnchoredPath -> Blob m -> Blob m -> a) -> Tree m -> Tree m -> [a]

For every pair of corresponding blobs from the two supplied trees, evaluate the supplied function and accumulate the results in a list. Hint: to get IO actions through, just use sequence on the resulting list. NB. This won't expand any stubs.

zipFiles :: (AnchoredPath -> Maybe (Blob m) -> Maybe (Blob m) -> a) -> Tree m -> Tree m -> [a]

For each file in each of the two supplied trees, evaluate the supplied function (supplying the corresponding file from the other tree, or Nothing) and accumulate the results in a list. Hint: to get IO actions through, just use sequence on the resulting list. NB. This won't expand any stubs.

zipTrees :: (AnchoredPath -> Maybe (TreeItem m) -> Maybe (TreeItem m) -> a) -> Tree m -> Tree m -> [a]

diffTrees :: forall m. (Functor m, Monad m) => Tree m -> Tree m -> m (Tree m, Tree m)

Cautiously extracts differing subtrees from a pair of Trees. It will never do any unneccessary expanding. Tree hashes are used to cut the comparison as high up the Tree branches as possible. The result is a pair of trees that do not share any identical subtrees. They are derived from the first and second parameters respectively and they are always fully expanded. It might be advantageous to feed the result into zipFiles or zipTrees.

Files (Blobs).

readBlob :: Blob m -> m ByteString

Read a Blob into a Lazy ByteString. Might be backed by an mmap, use with care.

Filtering trees.

class Monad m => FilterTree a m where

Methods

filter :: (AnchoredPath -> TreeItem m -> Bool) -> a m -> a m

Given pred tree, produce a Tree that only has items for which pred returns True. The tree might contain stubs. When expanded, these will be subject to filtering as well.

Instances

Monad m => FilterTree Tree m

FilterTree IndexM IO

restrict :: (FilterTree t m, Monad n) => Tree n -> t m -> t m

Given two Trees, a guide and a tree, produces a new Tree that is a identical to tree, but only has those items that are present in both tree and guide. The guide Tree may not contain any stubs.

Manipulating trees.

modifyTree :: Monad m => Tree m -> AnchoredPath -> Maybe (TreeItem m) -> Tree m

Modify a Tree (by replacing, or removing or adding items).

updateTree :: (Functor m, Monad m) => (TreeItem m -> m (TreeItem m)) -> Tree m -> m (Tree m)

Does not expand the tree.

updateSubtrees :: (Tree m -> Tree m) -> Tree m -> Tree m

overlay :: (Functor m, Monad m) => Tree m -> Tree m -> Tree m

Lay one tree over another. The resulting Tree will look like the base (1st parameter) Tree, although any items also present in the overlay Tree will be taken from the overlay. It is not allowed to overlay a different kind of an object, nor it is allowed for the overlay to add new objects to base. This means that the overlay Tree should be a subset of the base Tree (although any extraneous items will be ignored by the implementation).