struct::tree_v1 - Create and manipulate tree objects
The ::struct::tree command creates a new tree object with an associated global Tcl command whose name is treeName. This command may be used to invoke various operations on the tree. It has the following general form:
Option and the args determine the exact behavior of the command.
A tree is a collection of named elements, called nodes, one of which is distinguished as a root, along with a relation ("parenthood") that places a hierarchical structure on the nodes. (Data Structures and Algorithms; Aho, Hopcroft and Ullman; Addison-Wesley, 1987). In addition to maintaining the node relationships, this tree implementation allows any number of keyed values to be associated with each node.
The element names can be arbitrary strings.
A tree is thus similar to an array, but with three important differences:
Trees are accessed through an object command, whereas arrays are accessed as variables. (This means trees cannot be local to a procedure.)
Trees have a hierarchical structure, whereas an array is just an unordered collection.
Each node of a tree has a separate collection of attributes and values. This is like an array where every value is a dictionary.
The following commands are possible for tree objects:
Appends a value to one of the keyed values associated with an node. If no key is specified, the key data is assumed.
Return a list of the children of node.
Removes the node specified by node from the tree, but not its children. The children of node are made children of the parent of the node, at the index at which node was located.
Removes the specified nodes from the tree. All of the nodes' children will be removed as well to prevent orphaned nodes.
Return the number of steps from node node to the root node.
Destroy the tree, including its storage space and associated command.
Returns true if the specified node exists in the tree.
Return the value associated with the key key for the node node. If no key is specified, the key data is assumed.
Returns a serialized list of key/value pairs (suitable for use with [array set]) for the node.
Returns a list of keys for the node.
Return true if the specified key exists for the node. If no key is specified, the key data is assumed.
Returns the index of node in its parent's list of children. For example, if a node has nodeFoo, nodeBar, and nodeBaz as children, in that order, the index of nodeBar is 1.
Insert one or more nodes into the tree as children of the node parent. The nodes will be added in the order they are given. If parent is root, it refers to the root of the tree. The new nodes will be added to the parent node's child list at the index given by index. The index can be end in which case the new nodes will be added after the current last child.
If any of the specified children already exist in treeName, those nodes will be moved from their original location to the new location indicated by this command.
If no child is specified, a single node will be added, and a name will be generated for the new node. The generated name is of the form nodex, where x is a number. If names are specified they must neither contain whitespace nor colons (":").
The return result from this command is a list of nodes added.
Returns true if node is a leaf of the tree (if node has no children), false otherwise.
Appends a value (as a list) to one of the keyed values associated with an node. If no key is specified, the key data is assumed.
Make the specified nodes children of parent, inserting them into the parent's child list at the index given by index. Note that the command will take all nodes out of the tree before inserting them under the new parent, and that it determines the position to place them into after the removal, before the re-insertion. This behaviour is important when it comes to moving one or more nodes to a different index without changing their parent node.
Return the right sibling of node, or the empty string if node was the last child of its parent.
Return the number of immediate children of node.
Return the parent of node.
Return the left sibling of node, or the empty string if node was the first child of its parent.
Set or get one of the keyed values associated with a node. If no key is specified, the key data is assumed. Each node that is added to a tree has the value "" assigned to the key data automatically. A node may have any number of keyed values associated with it. If value is not specified, this command returns the current value assigned to the key; if value is specified, this command assigns that value to the key.
Return a count of the number of descendants of the node node; if no node is specified, root is assumed.
Insert a node named child into the tree as a child of the node parent. If parent is root, it refers to the root of the tree. The new node will be added to the parent node's child list at the index given by from. The children of parent which are in the range of the indices from and to are made children of child. If the value of to is not specified it defaults to end. If no name is given for child, a name will be generated for the new node. The generated name is of the form nodex, where x is a number. The return result from this command is the name of the new node.
Swap the position of node1 and node2 in the tree.
Removes a keyed value from the node node. If no key is specified, the key data is assumed.
Perform a breadth-first or depth-first walk of the tree starting at the node node. The type of walk, breadth-first or depth-first, is determined by the value of type; bfs indicates breadth-first, dfs indicates depth-first. Depth-first is the default. The order of the walk, pre-, post-, both- or in-order is determined by the value of order; pre indicates pre-order, post indicates post-order, both indicates both-order and in indicates in-order. Pre-order is the default.
Pre-order walking means that a parent node is visited before any of its children. For example, a breadth-first search starting from the root will visit the root, followed by all of the root's children, followed by all of the root's grandchildren. Post-order walking means that a parent node is visited after any of its children. Both-order walking means that a parent node is visited before and after any of its children. In-order walking means that a parent node is visited after its first child and before the second. This is a generalization of in-order walking for binary trees and will do the right thing if a binary is walked. The combination of a breadth-first walk with in-order is illegal.
As the walk progresses, the command cmd will be evaluated at each node. Percent substitution will be performed on cmd before evaluation, just as in a bind script. The following substitutions are recognized:
Insert the literal % character.
Name of the tree object.
Name of the current node.
Name of the action occurring; one of enter, leave, or visit. enter actions occur during pre-order walks; leave actions occur during post-order walks; visit actions occur during in-order walks. In a both-order walk, the command will be evaluated twice for each node; the action is enter for the first evaluation, and leave for the second.
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category struct :: tree of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.