Provided by: tcllib_1.15-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
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 SF Trackers
[http://sourceforge.net/tracker/?group_id=12883]. Please also report any ideas for enhancements you may
have for either package and/or documentation.
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>