mem t k is an Lwt promise that resolves to true iff k is bound to a value in t.

mem_tree t k is like mem but for trees.

get t k is an Lwt promise that resolves to Ok v if k is bound to the value v in t and Storage_ErrorMissing_key otherwise.

get_tree is like get but for trees.

find t k is an Lwt promise that resolves to Some v if k is bound to the value v in t and None otherwise.

find_tree t k is like find but for trees.

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.

init t k v is an Lwt promise that resolves to Ok c if:

• k is unbound in t;
• k is bound to v in c;
• and c is similar to t otherwise.

It is Storage_errorExisting_key if k is already bound in t.

init_tree is like init but for trees.

update t k v is an Lwt promise that resolves to Ok c if:

• k is bound in t;
• k is bound to v in c;
• and c is similar to t otherwise.

It is Storage_errorMissing_key if k is not already bound in t.

update_tree is like update but for trees.

add t k v is an Lwt promise that resolves to c such that:

• k is bound to v in c;
• and c is similar to t otherwise.

If k was already bound in t to a value that is physically equal to v, the result of the function is a promise that resolves to t. Otherwise, the previous binding of k in t disappears.

add_tree is like add but for trees.

remove t k v is an Lwt promise that resolves to c such that:

• k is unbound in c;
• and c is similar to t otherwise.

remove_existing t k v is an Lwt promise that resolves to Ok c if:

• k is bound in t to a value;
• k is unbound in c;
• and c is similar to t otherwise.

remove_existing_tree t k v is an Lwt promise that reolves to Ok c if:

• k is bound in t to a tree;
• k is unbound in c;
• and c is similar to t otherwise.

add_or_remove t k v is:

• add t k x if v is Some x;
• remove t k otherwise.

add_or_remove_tree t k v is:

• add_tree t k x if v is Some x;
• remove t k otherwise.

fold ?depth t root ~order ~init ~f recursively folds over the trees and values of t. The f callbacks are called with a key relative to root. f is never called with an empty key for values; i.e., folding over a value is a no-op.

The depth is 0-indexed. If depth is set (by default it is not), then f is only called when the conditions described by the parameter is true:

• Eq d folds over nodes and values of depth exactly d.
• Lt d folds over nodes and values of depth strictly less than d.
• Le d folds over nodes and values of depth less than or equal to d.
• Gt d folds over nodes and values of depth strictly more than d.
• Ge d folds over nodes and values of depth more than or equal to d.

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

config t is t's hash configuration.

length t key is an Lwt promise that resolves to the number of files and sub-nodes stored under k in t.

It is equivalent to list t k >|= List.length but has a constant-time complexity.

Most of the time, this function does not perform any I/O as the length is cached in the tree. It may perform one read to load the root node of the tree in case it has not been loaded already. The initial constant is the same between list and length. They both perform the same kind of I/O reads. While list usually performs a linear number of reads, length does at most one.