Module S.Tree

empty () is the empty tree. The empty tree does not have associated backend configuration values, as they can perform in-memory operation, independently of any given backend.

singleton k c is the tree with a single binding mapping the key k to the contents c.

of_contents c is the subtree built from the contents c.

of_node n is the subtree built from the node n.

The type for tree elements.

General-purpose constructor for trees.

pruned h is a purely in-memory tree with the hash h. Such trees can be used as children of other in-memory tree nodes, for instance in order to compute the hash of the parent, but they cannot be dereferenced.

Any operation that would require loading the contents of a pruned node (e.g. calling find on one of its children) will instead raise a Pruned_hash exception. Attempting to export a tree containing pruned sub-trees to a repository will fail similarly.

kind t k is the type of s in t. It could either be a tree node or some file contents. It is None if k is not present in t.

is_empty t is true iff t is empty (i.e. a tree node with no children). Trees with kind = `Contents are never considered empty.

diff x y is the difference of contents between x and y.

The exception raised by functions that can force lazy tree nodes but do not return an explicit or_error.

The exception raised by functions that attempts to load pruned tree nodes.

The exception raised by functions that attemps to perform IO on a portable tree.

Operations on lazy tree contents.

mem t k is true iff k is associated to some contents in t.

find_all t k is Some (b, m) if k is associated to the contents b and metadata m in t and None if k is not present in t.

length t key is the number of files and sub-nodes stored under key in t.

It is equivalent to List.length (list t k) but backends might optimise this call: for instance it's a constant time operation in irmin-pack.

cache defaults to true, see caching for an explanation of the parameter.

find is similar to find_all but it discards metadata.

Same as find_all but raise Invalid_arg if k is not present in t.

list t key is the list of files and sub-nodes stored under k in t. The result order is not specified but is stable.

offset and length are used for pagination.

cache defaults to true, see caching for an explanation of the parameter.

seq t key follows the same behavior as list but returns a sequence.

Same as get_all but ignore the metadata.

add t k c is the tree where the key k is bound to the contents c but is similar to t for other bindings.

update t k f is the tree t' that is the same as t for all keys except k, and whose binding for k is determined by f (find t k).

If k refers to an internal node of t, f is called with None to determine the value with which to replace it.

remove t k is the tree where k bindings has been removed but is similar to t for other bindings.

mem_tree t k is false iff find_tree k = None.

find_tree t k is Some v if k is associated to v in t. It is None if k is not present in t.

get_tree t k is v if k is associated to v in t. Raise Invalid_arg if k is not present in t.

add_tree t k v is the tree where the key k is bound to the non-empty tree v but is similar to t for other bindings.

If v is empty, this is equivalent to remove t k.

update_tree t k f is the tree t' that is the same as t for all subtrees except under k, and whose subtree at k is determined by f (find_tree t k).

f returning either None or Some empty causes the subtree at k to be unbound (i.e. it is equivalent to remove t k).

merge is the 3-way merge function for trees.

General-purpose destructor for trees.

The type for fold marks.

empty_marks () is an empty collection of marks.

The type for fold's force parameter. `True forces the fold to read the objects of the lazy nodes and contents. `False f is applying f on every lazy node and content value instead.

The type for fold's uniq parameters. `False folds over all the nodes. `True does not recurse on nodes already seen. `Marks m uses the collection of marks m to store the cache of keys: the fold will modify m. This can be used for incremental folds.

The type for fold's folders: pre, post, contents, node, and tree, where 'a is the accumulator and 'b is the item folded.

The type for fold depths.

• Eq d folds over nodes and contents of depth exactly d.
• Lt d folds over nodes and contents of depth strictly less than d.
• Gt d folds over nodes and contents of depth strictly more than d.

Le d is Eq d and Lt d. Ge d is Eq d and Gt d.

fold t acc folds over t's nodes with node-specific folders: contents, node, and tree, based on a node's kind.

The default for all folders is identity.

For every node n of t, including itself:

• If n is a `Contents kind, call contents path c where c is the contents of n.
• If n is a `Node kind, (1) call pre path steps; (2) call node path n; (3) recursively fold on each child; (4) call post path steps.
• If n is any kind, call tree path t' where t' is the tree of n.

See examples/fold.ml for a demo of the different folders.

See force for details about the force parameters. By default it is `True.

See uniq for details about the uniq parameters. By default it is `False.

The fold depth is controlled by the depth parameter.

cache defaults to false, see caching for an explanation of the parameter.

If order is `Sorted (the default), the elements are traversed in lexicographic order of their keys. If `Random state, they are traversed in a random order. For large nodes, these two modes are memory-consuming, use `Undefined for a more memory efficient fold.

The type for tree stats.

stats ~force t are t's statistics. If force is true, this will force the reading of lazy nodes. By default it is false.

The type for concrete trees.

of_concrete c is the subtree equivalent of the concrete tree c.

• raises Invalid_argument

  if c contains duplicate bindings for a given path.

to_concrete t is the concrete tree equivalent of the subtree t.

clear ?depth t clears all caches in the tree t for subtrees with a depth higher than depth. If depth is not set, all of the subtrees are cleared.

A call to clear doesn't discard the subtrees of t, only their cache are discarded. Even the lazily loaded and unmodified subtrees remain.

inspect t is similar to kind, with additional state information for nodes. It is primarily useful for debugging and testing.

If t holds a node, additional information about its state is included:

• `Map, if t is from of_concrete.
• `Value, if t's node has modifications that have not been persisted to a store.
• `Portable_dirty, if t's node has modifications and is Node.Portable. Currently only used with Proof.
• `Pruned, if t is from pruned.
• Otherwise `Key, the default state for a node loaded from a store.

pp is a pretty-printer for a tree.

Keys in the Irmin store are tagged with the type of the value they reference (either contents or node). In the contents case, the key is paired with corresponding metadata.

key t is the key of tree t in the underlying repository, if it exists. Tree objects that exist entirely in memory (such as those built with of_concrete) have no backend key until they are exported to a repository, and so will return None.

find_key r t is the key of a tree object with the same hash as t in r, if such a key exists and is indexed.

of_key r h is the tree object in r having h as key, or None if no such tree object exists.

shallow r h is the shallow tree object with the key h. No check is performed to verify if h actually exists in r.

hash t is the hash of tree t.

Like kinded_key, but with hashes as value references rather than keys.

kinded_hash t is c's kinded hash.

of_hash r h is the tree object in r with hash h, or None if no such tree object is indexed in r.

Note: in stores for which node_key = contents_key = hash, this function has identical behaviour to of_key.

produce r h f runs f on top of a real store r, producing a proof and a result using the initial root hash h.

The trees produced during f's computation will carry the full history of reads. This history will be reset when f is complete so subtrees escaping the scope of f will not cause memory leaks.

Calling produce_proof recursively has an undefined behaviour.

The type for errors associated with functions that verify proofs.

verify p f runs f in checking mode. f is a function that takes a tree as input and returns a new version of the tree and a result. p is a proof, that is a minimal representation of the tree that contains what f should be expecting.

Therefore, contrary to trees found in a storage, the contents of the trees passed to f may not be available. For this reason, looking up a value at some path can now produce three distinct outcomes:

• A value v is present in the proof p and returned : find tree path is a promise returning Some v;
• path is known to have no value in tree : find tree path is a promise returning None; and
• path is known to have a value in tree but p does not provide it because f should not need it: verify returns an error classifying path as an invalid path (see below).

The same semantics apply to all operations on the tree t passed to f and on all operations on the trees built from f.

The generated tree is the tree after f has completed. That tree is disconnected from the backend. It is possible to run operations on it as long as they don't require loading shallowed subtrees, otherwise it would raise Dangling_hash.

The result is Error _ if the proof is rejected:

• when p.before is different from the hash of p.state;
• when p.after is different from the hash of f p.state;
• when f p.state tries to access paths invalid paths in p.state;

produce_proof is the producer of tree proofs.

verify_proof is the verifier of tree proofs.