Provided by: tcllib_1.19-dfsg-2_all 
NAME
treeql - Query tree objects
SYNOPSIS
package require Tcl 8.2
package require snit
package require struct::list
package require struct::set
package require treeql ?1.3.1?
treeql objectname -tree tree ?-query query? ?-nodes nodes? ?args...?
qo query args...
qo result
qo discard
_________________________________________________________________________________________________
DESCRIPTION
This package provides objects which can be used to query and transform tree objects
following the API of tree objects created by the package struct::tree.
The tree query and manipulation language used here, TreeQL, is inspired by Cost (See
section References for more information).
treeql, the package, is a fairly thin query facility over tree-structured data types. It
implements an ordered set of nodes (really a list) which are generated and filtered
through the application of TreeQL operators to each node in turn.
API
TREEQL CLASS API
The command treeql is a snit::type which implements the Treeql Query Language. This means
that it follows the API for class commands as specified by the package snit. Its general
syntax is
treeql objectname -tree tree ?-query query? ?-nodes nodes? ?args...?
The command creates a new tree query object and returns the fully qualified name of
the object command as its result. The API the returned command is following is
described in the section TreeQL OBJECT API
Each query object is associated with a single tree object. This is the object all
queries will be run against.
If the option -nodes was specified then its argument is treated as a list of nodes.
This list is used to initialize the node set. It defaults to the empty list.
If the option -query was specified then its argument will be interpreted as an
object, the parent query of this query. It defaults to the object itself. All
queries will be interpreted in the environment of this object.
Any arguments coming after the options are treated as a query and run immediately,
after the node set has been initialized. This uses the same syntax for the query as
the method query.
The operations of the TreeQL available for this are explained in the section about
The Tree Query Language. This section also explains the term node set used above.
TREEQL OBJECT API
As treeql has been implemented in snit all the standard methods of snit-based classes are
available to the user and therefore not listed here. Please read the documentation for
snit for what they are and what functionality they provide
The methods provided by the package treeql itself are listed and explained below.
qo query args...
This method interprets its arguments as a series of TreeQL operators and
interpretes them from the left to right (i.e. first to last). Note that the first
operator uses the node set currently known to the object to perform its actions.
In other words, the node set is not cleared, or modified in other ways, before the
query is run. This allows the user to run several queries one after the other and
have each use the results of the last. Any initialization has to be done by any
query itself, using TreeQL operators. The result of the method is the node set
after the last operator of the query has been executed.
Note that uncaught errors will leave the node set of the object in an intermediate
state, per the TreeQL operators which were executed successfully before the error
occurred.
The above means in detail that:
[1] The first argument is interpreted as the name of a query operator, the
number of arguments required by that operator is then determined, and taken
from the immediately following arguments.
Because of this operators cannot have optional arguments, all arguments have
to be present as defined. Failure to do this will, at least, confuse the
query interpreter, but more likely cause errors.
[2] The operator is applied to the current node set, yielding a new node set,
and/or manipulating the tree object the query object is connected to.
[3] The arguments used (i.e. operator name and arguments) are removed from the
list of method arguments, and then the whole process is repeated from step
[1], until the list of arguments is empty or an error occurred.
# q is the query object.
q query root children get data
# The above query
# - Resets the node set to the root node - root
# - Adds the children of root to the set - children
# - Replaces the node set with the - get data
# values for the attribute 'data',
# for all nodes in the set which
# have such an attribute.
# - And returns this information.
# Below we can see the same query, but rewritten
# to show the structure as it is seen by the query
# interpreter.
q query \\
root \\
children \\
get data
The operators of the TreeQL language available for this are explained in the section about
The Tree Query Language. This section also explains the term node set used above.
qo result
This method returns a list containing the current node set.
qo discard
This method returns the current node set (like method result), but also destroys
the query object (qo). This is useful when constructing and using sub-queries
(%AUTO% objects immediately destroyed after use).
THE TREE QUERY LANGUAGE
This and the following sections specify the Tree Query Language used by the query objects
of this package in detail.
First we explain the general concepts underneath the language which are required to
comprehend it. This is followed by the specifications for all the available query
operators. They fall into eight categories, and each category has its own section.
[1] TreeQL Concepts
[2] Structural generators
[3] Attribute Filters
[4] Attribute Mutators
[5] Attribute String Accessors
[6] Sub-queries
[7] Node Set Operators
[8] Node Set Iterators
[9] Typed node support
TREEQL CONCEPTS
The main concept which has to be understood is that of the node set. Each query object
maintains exactly one such node set, and essentially all operators use it and input
argument and for their result. This structure simply contains the handles of all nodes
which are currently of interest to the query object. To name it a set is a bit of a
misnomer, because
[1] A node (handle) can occur in the structure more than once, and
[2] the order of nodes in the structure is important as well. Whenever an operator
processes all nodes in the node set it will do so in the order they occur in the
structure.
Regarding the possible multiple occurrence of a node, consider a node set containing two
nodes A and B, both having node P as their immediate parent. Application of the TreeQL
operator "parent" will then add P to the new node set twice, once per node it was parent
of. I.e. the new node set will then be {P P}.
STRUCTURAL GENERATORS
All tree-structural operators locate nodes in the tree based on a structural relation ship
to the nodes currently in the set and then replace the current node set with the set of
nodes found Nodes which fulfill such a relationship multiple times are added to the result
as often as they fulfill the relationship.
It is important to note that the found nodes are collected in a separate storage area
while processing the node set, and are added to (or replacing) the current node set only
after the current node set has been processed completely. In other words, the new nodes
are not processed by the operator as well and do not affect the iteration.
When describing an operator the variable N will be used to refer to any node in the node
set.
ancestors
Replaces the current node set with the ancestors for all nodes N in the node set,
should N have a parent. In other words, nodes without a parent do not contribute to
the new node set. In other words, uses all nodes on the path from node N to root,
in this order (root last), for all nodes N in the node set. This includes the root,
but not the node itself.
rootpath
Replaces the current node set with the ancestors for all nodes N in the node set,
should N have a parent. In other words, nodes without a parent do not contribute to
the new node set. In contrast to the operator ancestors the nodes are added in
reverse order however, i.e. the root node first.
parent Replaces the current node set with the parent of node N, for all nodes N in the
node set, should N have a parent. In other words, nodes without a parent do not
contribute to the new node set.
children
Replaces the current node set with the immediate children of node N, for all nodes
N in the node set, should N have children. In other words, nodes without children
do not contribute to the new node set.
left Replaces the current node set with the previous/left sibling for all nodes N in the
node set, should N have siblings to the left. In other words, nodes without left
siblings do not contribute to the new node set.
right Replaces the current node set with the next/right sibling for all nodes N in the
node set, should N have siblings to the right. In other words, nodes without right
siblings do not contribute to the new node set.
prev Replaces the current node set with all previous/left siblings of node N, for all
nodes N in the node set, should N have siblings to the left. In other words, nodes
without left siblings are ignored. The left sibling adjacent to the node is added
first, and the leftmost sibling last (reverse tree order).
esib Replaces the current node set with all previous/left siblings of node N, for all
nodes N in the node set, should N have siblings to the left. In other words, nodes
without left siblings are ignored. The leftmost sibling is added first, and the
left sibling adjacent to the node last (tree order).
The method name is a shorthand for Earlier SIBling.
next Replaces the current node set with all next/right siblings of node N, for all nodes
N in the node set, should N have siblings to the right. In other words, nodes
without right siblings do not contribute to the new node set. The right sibling
adjacent to the node is added first, and the rightmost sibling last (tree order).
root Replaces the current node set with a node set containing a single node, the root of
the tree.
tree Replaces the current node set with a node set containing all nodes found in the
tree. The nodes are added in pre-order (parent first, then children, the latter
from left to right, first to last).
descendants
Replaces the current node set with the nodes in all subtrees rooted at node N, for
all nodes N in the node set, should N have children. In other words, nodes without
children do not contribute to the new node set.
This is like the operator children, but covers the children of children as well,
i.e. all the proper descendants. "Rooted at N" means that N itself is not added to
the new set, which is also implied by proper descendants.
subtree
Like operator descendants, but includes the node N. In other words:
Replaces the current node set with the nodes of the subtree of node N, for all
nodes N in the node set, should N have children. In other words, nodes without
children do not contribute to the new node set. I.e this is like the operator
children, but covers the children of children, etc. as well. "Of N" means that N
itself is added to the new set.
forward
Replaces the current node set with the nodes in the subtrees rooted at the right
siblings of node N, for all nodes N in the node set, should N have right siblings,
and they children. In other words, nodes without right siblings, and them without
children are ignored.
This is equivalent to the operator sequence
next descendants
later This is an alias for the operator forward.
backward
Replaces the current node set with the nodes in the flattened previous subtrees, in
reverse tree order.
This is nearly equivalent to the operator sequence
prev descendants
The only difference is that this uses the nodes in reverse order.
earlier
Replaces the current node set with the nodes in the flattened previous subtrees, in
tree order.
This is equivalent to the operator sequence
prev subtree
ATTRIBUTE FILTERS
These operators filter the node set by reference to attributes of nodes and their
properties. Filter means that all nodes not fulfilling the criteria are removed from the
node set. In other words, the node set is replaced by the set of nodes fulfilling the
filter criteria.
hasatt attr
Reduces the node set to nodes which have an attribute named attr.
withatt attr value
Reduces the node set to nodes which have an attribute named attr, and where the
value of that attribute is equal to value (The "==" operator is string equal
-nocase).
withatt! attr val
This is the same as withatt, but all nodes in the node set have to have the
attribute, and the "==" operator is string equal, i.e. no -nocase. The operator
will fail with an error if they don't have the attribute.
attof attr vals
Reduces the node set to nodes which which have an attribute named attr and where
the value of that attribute is contained in the list vals of legal values. The
contained-in operator used here does glob matching (using the attribute value as
pattern) and ignores the case of the attribute value, but not for the elements of
vals.
attmatch attr match
Same as withatt, but string match is used as the "==" operator, and match is the
pattern checked for.
Note that match is a interpreted as a partial argument list for string match. This
means that it is interpreted as a list containing the pattern, and the pattern
element can be preceded by options understand by string match, like -nocase. This
is especially important should the pattern contain spaces. It has to be wrapped
into a list for correct interpretation by this operator
ATTRIBUTE MUTATORS
These operators change node attributes within the underlying tree. In other words, all
these operators have side effects.
set attr val
Sets the attribute attr to the value val, for all nodes N in the node set. The
operator will fail if a node does not have an attribute named attr. The tree will
be left in a partially modified state.
unset attr
Unsets the attribute attr, for all nodes N in the node set. The operator will fail
if a node does not have an attribute named attr. The tree will be left in a
partially modified state.
ATTRIBUTE STRING ACCESSORS
These operators retrieve the values of node attributes from the underlying tree. The
collected results are stored in the node set, but are not actually nodes.
In other words, they redefine the semantics of the node set stored by the query object to
contain non-node data after their completion.
The query interpreter will terminate after it has finished processing one of these
operators, silently discarding any later query elements. It also means that our talk
about maintenance of a node set is not quite true. It is a node set while the interpreter
is processing commands, but can be left as an attribute value set at the end of query
processing.
string op attr
Applies the string operator op to the attribute named attr, for all nodes N in the
node set, collects the results of that application and places them into the node
set.
The operator will fail if a node does not have an attribute named attr.
The argument op is interpreted as partial argument list for the builtin command
string. Its first word has to be any of the sub-commands understood by string.
This has to be followed by all arguments required for the subcommand, except the
last. that last argument is supplied by the attribute value.
get pattern
For all nodes N in the node set it determines all their attributes with names
matching the glob pattern, then the values of these attributes, at last it replaces
the node set with the list of these attribute values.
attlist
This is a convenience definition for the operator getvals *. In other words, it
replaces the node set with a list of the attribute values for all attributes for
all nodes N in the node set.
attrs glob
Replaces the current node set with a list of attribute lists, one attribute list
per for all nodes N in the node set.
attval attname
Reduces the current node set with the operator hasatt, and then replaces it with a
list containing the values of the attribute named attname for all nodes N in the
node set.
SUB-QUERIES
Sub-queries yield node sets which are then used to augment, reduce or replace the current
node set.
andq query
Replaces the node set with the set-intersection of the node set generated by the
sub-query query and itself.
The execution of the sub-query uses the current node set as its own initial node
set.
orq query
Replaces the node set with the set-union of the node set generated by the sub-query
query and itself. Duplicate nodes are removed.
The execution of the sub-query uses the current node set as its own initial node
set.
notq query
Replaces the node set with the set of nodes generated by the sub-query query which
are also not in the current node set. In other word the set difference of itself
and the node set generated by the sub-query.
The execution of the sub-query uses the current node set as its own initial node
set.
NODE SET OPERATORS
These operators change the node set directly, without referring to the tree.
unique Removes duplicate nodes from the node set, preserving order. In other words, the
earliest occurrence of a node handle is preserved, every other occurrence is
removed.
select Replaces the current node set with a node set containing only the first node from
the current node set
transform query var body
First it interprets the sub-query query, using the current node set as its initial
node set. Then it iterates over the result of that query, binding the handle of
each node to the variable named in var, and executing the script body. The
collected results of these executions is made the new node set, replacing the
current one.
The script body is executed in the context of the caller.
map var body
Iterates over the current node set, binding the handle of each node to the variable
named in var, and executing the script body. The collected results of these
executions is made the new node set, replacing the current one.
The script body is executed in the context of the caller.
quote val
Appends the literal value val to the current node set.
replace val
Replaces the current node set with the literal list value val.
NODE SET ITERATORS
foreach query var body
Interprets the sub-query query, then performs the equivalent of operator over on
the nodes in the node set created by that query. The current node set is not
changed, except through side effects from the script body.
The script body is executed in the context of the caller.
with query body
Interprets the query, then runs the script body on the node set generated by the
query. At last it restores the current node set as it was before the execution of
the query.
The script body is executed in the context of the caller.
over var body
Executes the script body for each node in the node set, with the variable named by
var bound to the name of the current node. The script body is executed in the
context of the caller.
This is like the builtin foreach, with the node set as the source of the list to
iterate over.
The results of executing the body are ignored.
delete Deletes all the nodes contained in the current node set from the tree.
TYPED NODE SUPPORT
These filters and accessors assume the existence of an attribute called @type, and are
short-hand forms useful for cost-like tree query, html tree editing, and so on.
nodetype
Returns the node type of nodes. Attribute string accessor. This is equivalent to
get @type
oftype t
Reduces the node set to nodes whose type is equal to t, with letter case ignored.
nottype t
Reduces the node set to nodes whose type is not equal to t, with letter case
ignored.
oftypes attrs
Reduces set to nodes whose @type is an element in the list attrs of types. The
value of @type is used as a glob pattern, and letter case is relevant.
EXAMPLES
... TODO ...
REFERENCES
[1] COST [http://wiki.tcl.tk/COST] on the Tcler's Wiki.
[2] TreeQL [http://wiki.tcl.tk/treeql] on the Tcler's Wiki. Discuss this package there.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other
problems. Please report such in the category treeql of the Tcllib Trackers
[http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for enhancements you
may have for either package and/or documentation.
When proposing code changes, please provide unified diffs, i.e the output of diff -u.
Note further that attachments are strongly preferred over inlined patches. Attachments can
be made by going to the Edit form of the ticket immediately after its creation, and then
using the left-most button in the secondary navigation bar.
KEYWORDS
Cost, DOM, TreeQL, XPath, XSLT, structured queries, tree, tree query language
CATEGORY
Data structures
COPYRIGHT
Copyright (c) 2004 Colin McCormack <coldstore@users.sourceforge.net>
Copyright (c) 2004 Andreas Kupries <andreas_kupries@users.sourceforge.net>