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ensemble(n)                                      [incr Tcl]                                      ensemble(n)



____________________________________________________________________________________________________________

NAME
       ensemble - create or modify a composite command

SYNOPSIS
       itcl::ensemble ensName ?command arg arg...?
       or
       ensemble ensName {
           part partName args body
           ...
           ensemble partName {
               part subPartName args body
               part subPartName args body
           ...
           }
       }
____________________________________________________________________________________________________________


DESCRIPTION
       The  ensemble  command  is  used to create or modify a composite command.  See the section WHAT IS AN
       ENSEMBLE? below for a brief overview of ensembles.

       If the ensemble command finds an existing ensemble called ensName, it updates that ensemble.   Other-wise, Otherwise,
       wise,  it  creates  an  ensemble called ensName.  If the ensName is a simple name like "foo", then an
       ensemble command named "foo" is added to the current namespace context.  If  a  command  named  "foo"
       already  exists  in  that  context, then it is deleted.  If the ensName contains namespace qualifiers
       like "a::b::foo", then the namespace path is resolved, and the ensemble command is added that  names-pace namespace
       pace context.  Parent namespaces like "a" and "b" are created automatically, as needed.

       If  the  ensName contains spaces like "a::b::foo bar baz", then additional words like "bar" and "baz"
       are treated as sub-ensembles.  Sub-ensembles are merely parts within an ensemble; they do not have  a
       Tcl  command  associated with them.  An ensemble like "foo" can have a sub-ensemble called "foo bar",
       which in turn can have a sub-ensemble called "foo bar baz".  In this case, the sub-ensemble "foo bar"
       must be created before the sub-ensemble "foo bar baz" that resides within it.

       If  there  are  any arguments following ensName, then they are treated as commands, and they are exe-cuted executed
       cuted to update the ensemble.  The following commands are  recognized  in  this  context:   part  and
       ensemble.

       The part command defines a new part for the ensemble.  Its syntax is identical to the usual proc com-mand, command,
       mand, but it defines a part within an ensemble, instead of a Tcl command.  If a part called  partName
       already exists within the ensemble, then the part command returns an error.

       The ensemble command can be nested inside another ensemble command to define a sub-ensemble.


WHAT IS AN ENSEMBLE?
       The usual "info" command is a composite command--the command name info must be followed by a sub-com-mand sub-command
       mand like body or globals.  We will refer to a command like info as an ensemble, and to  sub-commands
       like body or globals as its parts.

       Ensembles  can  be  nested.   For example, the info command has an ensemble info namespace within it.
       This ensemble has parts like info namespace all and info namespace children.

       With ensembles, composite commands can be created and extended in an automatic way.  Any package  can
       find an existing ensemble and add new parts to it.  So extension writers can add their own parts, for
       example, to the info command.

       The ensemble facility manages all of the part names and keeps track of  unique  abbreviations.   Nor-mally, Normally,
       mally,  you  can  abbreviate info complete to info comp.  But if an extension adds the part info com-plexity, complexity,
       plexity, the minimum abbreviation for info complete becomes info complet.

       The ensemble facility not only automates the construction of composite commands, but it automates the
       error handling as well.  If you invoke an ensemble command without specifying a part name, you get an
       automatically generated error message that summarizes the usage information.  For example,  when  the
       info command is invoked without any arguments, it produces the following error message:
              wrong # args: should be one of...
                info args procname
                info body procname
                info cmdcount
                info commands ?pattern?
                info complete command
                info context
                info default procname arg varname
                info exists varName
                info globals ?pattern?
                info level ?number?
                info library
                info locals ?pattern?
                info namespace option ?arg arg ...?
                info patchlevel
                info procs ?pattern?
                info protection ?-command? ?-variable? name
                info script
                info tclversion
                info vars ?pattern?
                info which ?-command? ?-variable? ?-namespace? name
       You  can  also  customize  the  way  an  ensemble responds to errors.  When an ensemble encounters an
       unspecified or ambiguous part name, it looks for a part called @error.  If it exists, then it is used
       to  handle  the error.  This part will receive all of the arguments on the command line starting with
       the offending part name.  It can find another way of resolving the command, or generate its own error
       message.


EXAMPLE
       We could use an ensemble to clean up the syntax of the various "wait" commands in Tcl/Tk.  Instead of
       using a series of strange commands like this:
              vwait x
              tkwait visibility .top
              tkwait window .
       we could use commands with a uniform syntax, like this:
              wait variable x
              wait visibility .top
              wait window .
       The Tcl package could define the following ensemble:
              itcl::ensemble wait part variable {name} {
                  uplevel vwait $name
              }
       The Tk package could add some options to this ensemble, with a command like this:
              itcl::ensemble wait {
                  part visibility {name} {
                      tkwait visibility $name
                  }
                  part window {name} {
                      tkwait window $name
                  }
              }
       Other extensions could add their own parts to the wait command too.


KEYWORDS
       ensemble, part, info



itcl                                                 3.0                                         ensemble(n)