KEYED LISTS
       Extended Tcl defines a special type of list referred to as
       keyed lists.  These lists provided a structured data  type
       built  upon standard Tcl lists.  This provides a function-
       ality similar to structs in the C programming language.

       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 com-
              poser}}}

       If the variable person  contained  the  above  list,  then
       keylget person NAME would return {Frank Zappa}.  Executing
       the command:

            keylset person ID 106

       would make person contain

                  {{ID 106} {NAME {Frank Zappa}}  {JOB  {musician
              and composer}}

       Fields may contain subfields; `.' is the separator charac-
       ter.  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 argu-
       ment  (i.e.  passed by reference), rather than passing the
       list directly.

       This functionality is provided by Extended Tcl.
