Purpose: to dicuss TclX's special keyed list functions.
From the TclX man page, you can read:
A keyed list is a list in which each element contains a key and value pair. These element pairs are stored as lists themselves, where the key is the first element of the list, and the value is the second. The key-value pairs are referred to as fields. This is an example of a keyed list:
{{NAME {Frank Zappa}} {JOB {musician and composer}}}
Fields may contain subfields; `.' is the separator character. Subfields are actually fields where the value is another keyed list. Thus the following list has the top level fields ID and NAME, and subfields NAME.FIRST and NAME.LAST:
{ID 106} {NAME {{FIRST Frank} {LAST Zappa}}}There is no limit to the recursive depth of subfields, allowing one to build complex data structures.
Keyed lists are constructed and accessed via a number of commands. All keyed list management commands take the name of the variable containing the keyed list as an argument (i.e. passed by reference), rather than passing the list directly.
Delete the field specified by key from the keyed list in the
variable listvar. This removes both the key and the value
from the keyed list.
keylget listvar ?key? ?retvar | {}?
Return the value associated with key from the keyed list in
the variable listvar. If retvar is not specified, then the
value will be returned as the result of the command. In this
case, if key is not found in the list, an error will result.
If retvar is specified and key is in the list, then the
value is returned in the variable retvar and the command
returns 1 if the key was present within the list. If key
isn't in the list, the command will return 0, and retvar
will be left unchanged. If {} is specified for retvar, the
value is not returned, allowing the Tcl programmer to deter-
mine if a key is present in a keyed list without setting a
variable as a side-effect.
If key is omitted, then a list of all the keys in the keyed
list is returned.
keylkeys listvar ?key?
Return the a list of the keys in the keyed list in the vari-
able listvar. If keys is specified, then it is the name of
a key field who's subfield keys are to be retrieve.
keylset listvar key value ?key2 value2 ...?
Set the value associated with key, in the keyed list con-
tained in the variable listvar, to value. If listvar does
not exists, it is created. If key is not currently in the
list, it will be added. If it already exists, value
replaces the existing value. Multiple keywords and values
may be specified, if desired.