package plebeia

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Module Plebeia.CursorSource

1 Zipper

2 Types: Trail and cursor

Sourcetype modified =
  1. | Modified
  2. | Unmodified of Node_type.indexed * Node_type.hashed
Sourcetype trail = private
  1. | Top
  2. | Left of trail * Node_type.node * modified
  3. | Right of Node_type.node * trail * modified
  4. | Budded of trail * modified
  5. | Extended of trail * Segment.t * modified

A trail represents the content of the memory stack when recursively exploring a tree. Constructing these trails from closure would be easier, but it would make it harder to port the code to C. The type parameters of the trail keep track of the type of each element on the "stack" using a product type.

The constructors are private. Use '_' prefixed functions with runtime invariant checks.

Sourcetype info = Info.t
Sourcetype cursor = private
  1. | Cursor of trail * Node_type.node * Context.t * info
    (*

    The cursor, also known as a zipper combines the information contained in a trail and a subtree to represent an edit point within a tree. This is a functional data structure that represents the program point in a function that modifies a tree. We use an existential type that keeps the .mli sane and enforces the most important: that the hole tags match between the trail and the Node

    *)
Sourcetype t = cursor

2 Constructor with invariant checks

Sourceval _Top : trail
Sourceval _Left : (trail * Node_type.node * modified) -> trail
Sourceval _Right : (Node_type.node * trail * modified) -> trail
Sourceval _Budded : (trail * modified) -> trail
Sourceval _Extended : (trail * Segment.t * modified) -> trail
Sourceval _Cursor : (trail * Node_type.node * Context.t * info) -> cursor

2 Creation

Sourceval empty : Context.t -> t

Creates a cursor to a new, empty tree.

2 Accessors

Sourceval context : t -> Context.t
Sourceval get_storage : t -> Storage.t
Sourceval index : t -> Index.t option

Get the index of the node pointed by the cursor, if indexed.

2 Segments

Sourceval path_of_trail : trail -> Path.t

Segment side list of the given trail, splitted by buds

Sourceval path_of_cursor : t -> Path.t

Segment side list of the given cursor, splitted by buds

Sourceval local_seg_of_trail : trail -> Segment.t

Segment side list of the given trail, splitted by buds

Sourceval local_seg_of_cursor : t -> Segment.t

Segment side list of the given cursor, splitted by buds

2 View

Sourceval view : t -> t * Node_type.view

Get the view of the cursor. Returns also the updated cursor with the view.

Sourceval may_forget : t -> t option

If the node pointed by the cursor is indexed, forget the details

2 Zipper functions

Sourcetype Error.t +=
  1. | Cursor_invariant of string
  2. | Write of string
  3. | Move of string

3 Simple 1 step cursor movement

Sourceval go_below_bud : t -> (t option, Error.t) Result.t

This function expects a cursor positionned on a bud and moves it one step below.

Sourceval go_down_extender : t -> (t, Error.t) Result.t

Go down an Extender node. The cursor must point to an Extender.

Sourceval go_side : Segment.side -> t -> (t, Error.t) Result.t

Go down an Internal node. The cursor must point to an Internal.

Sourceval go_up : t -> (t, Error.t) Result.t

Go up one level

3 Complex multi step cursor movement

Many of these functions fail when the given cursor does not point to a bud.

Sourcetype access_result =
  1. | Empty_bud
  2. | Collide of cursor * Node_type.view
  3. | Middle_of_extender of cursor * Segment.t * Segment.t * Segment.t
  4. | Reached of cursor * Node_type.view
  5. | HashOnly of cursor * Hash.t * Segment.t

Result of access_gen

Sourcetype Error.t +=
  1. | Access of access_result
Sourceval error_access : access_result -> ('a, Error.t) Result.t

Make an access result into an error

Sourceval access_gen : t -> Segment.t -> (access_result, Error.t) Result.t

Follow a segment. t must point to a bud. The function first go below the bud, then follow the segment.

Sourceval access_gen' : t -> Segment.t -> (access_result, Error.t) Result.t

Follow a segment. t can be any node.

Sourceval go_top : t -> t

Move up to the top

Sourceval go_up_to_bud : t -> (t, Error.t) Result.t

Moves the cursor back to the bud above. Note that this is not like "cd ../".

If the cursor is already at a bud, the cursor will move to its parent bud.

Sourceval parent : t -> (t, Error.t) Result.t

Moves the cursor back to the bud above. Like "cd ../". The cursor must point to a bud otherwise parent fails.

Sourceval subtree : t -> Segment.t -> (t, Error.t) Result.t

Moves the cursor down a segment, to the root of a sub-tree. Think "cd segment/"

Sourceval create_subtree : t -> Segment.t -> (t, Error.t) Result.t

Create a subtree (bud). Think "mkdir segment". The cursor does NOT move from the original position.

Sourceval subtree_or_create : t -> Segment.t -> (t, Error.t) Result.t

Same as subtree but create a subtree if not exists

Sourceval get : t -> Segment.t -> (t * [ `Leaf of Node_type.view | `Bud of Node_type.view ], Error.t) Result.t

Gets a value if present in the current tree at the given segment.

Sourceval get_value : t -> Segment.t -> (t * Value.t, Error.t) Result.t

Gets a value or a bud at the given segment.

Sourceval insert : t -> Segment.t -> Value.t -> (t, Error.t) Result.t

Inserts a value at the given segment in the current tree. It fails if a value already exists at the segment. The cursor does NOT move from the original position.

Sourceval upsert : t -> Segment.t -> Value.t -> (t, Error.t) Result.t

Upserts. If a value alrady exists at the segment, it is overwritten. This can still fail if the segment points to a subtree. The cursor does NOT move from the original position.

Sourceval update : t -> Segment.t -> Value.t -> (t, Error.t) Result.t

Update. A value must be bound at the segment.

Sourceval set_hashonly : t -> Segment.segment -> Hash.t -> (t, Error.t) result
Sourceval delete : t -> Segment.t -> (t, Error.t) Result.t

Delete a leaf or subtree. The cursor does NOT move from the original position.

Sourceval delete' : t -> Segment.t -> (t, Error.t) Result.t

Delete a node. The cursor does NOT move from the original position.

Sourceval remove_empty_bud : t -> (t, Error.t) Result.t

Remove the empty Bud pointed by the cursor. If the non-root parent becomes empty by the removal, remove_empty_bud recursively removes it, too. If the cursor points non empty bud, it does nothing.

The cursor in the result points to the parent bud of the upmost removed bud.

alter can easily break the invariants.

Sourceval forget_info : t -> t
Sourceval fold : init:'acc -> t -> ('acc -> t -> [< `Continue | `Exit | `Up ] * 'acc) -> 'acc

Folding over the node tree. The function can choose the node traversal from the given cursor: either continuing into its sub-nodes, not traversing its sub-nodes, or quit the entire folding.

If a node is shared at multiple places it is visited MORE THAN ONCE. If you want to avoid visiting a shared node at most once, carry a set of visited nodes by indices and check a node is visited or not.

Sourceval traverse : 'a -> t list -> ('a -> t -> [< `Exit | `Up | `Continue ] * 'a) -> 'a * t list

More generic tree traversal than fold, which has a step-by-step visitor interface: it does not recurse the structure by itself.

If a node is shared at multiple places it is visited MORE THAN ONCE.

2 Cursor hash compuation

Sourceval compute_hash : t -> t * Hash.t

Returns the hash of the node pointed by the cursor. It traverses nodes and compute hashes if necessary.

It also returns the updated cursor with the hash information.

Sourceval compute_hash' : (Node_type.t -> [< `Hashed of Hash.t * Node_type.t | `Not_Hashed of Node_type.view ]) -> t -> t * Hash.t

Compute the node hash of the node pointed by the given cursor. Tail recursive.

The function argument for short cutting, especially for Disk _. It can do either

* Obtain the node hash of the node somehow from an external source * Retrieve the view of the node to let compute' calculate the node hash of it

Sourceval is_with_count : t -> bool
Sourceval count_itself : t -> (int * t) option

count the leaves and buds, loading nodes on demand.

count_itself c returns 1 when c points to a Bud, not the numbers of the leaves and buds under the bud.

Returns None when the pagination count is not in the context.

Sourceval count : t -> (int * t) option

count the leaves and buds, loading nodes on demand.

count c, if c points to a Bud, it returns the number of the leaves and buds under c.

Returns None when the pagination count is not in the context.

2 Statistics

Sourceval stat : t -> Stat.t

2 Debug

Sourceval dot_of_cursor_ref : (t -> string) ref

Placeholder of Graphviz rendering of cursors

Sourcemodule Monad : sig ... end
Sourcemodule Cursor_storage : sig ... end
Sourceval deep_stat : int32 -> t -> unit Lwt.t

debug