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.so man.macros

.TH ensemble n 3.0 itcl "[incr\ Tcl]"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

ensemble \- create or modify a composite command

.SH SYNOPSIS

\fBensemble \fIensName\fR ?\fIcommand arg arg...\fR?

.br

or

.br

\fBensemble \fIensName\fR {

.br

    \fBpart \fIpartName args body\fR

.br

    \fI...\fR

.br

    \fBensemble \fIpartName\fR {

.br

        \fBpart \fIsubPartName args body\fR

.br

        \fBpart \fIsubPartName args body\fR

.br

    \fI...\fR

    }

.br

}

.BE

.SH DESCRIPTION

.PP

The \fBensemble\fR command is used to create or modify a composite

command.  See the section \fBWHAT IS AN ENSEMBLE?\fR below for a

brief overview of ensembles.

.PP

If the \fBensemble\fR command finds an existing ensemble called

\fIensName\fR, it updates that ensemble.  Otherwise, it creates an

ensemble called \fIensName\fR.  If the \fIensName\fR 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 \fIensName\fR contains

namespace qualifiers like "a::b::foo", then the namespace path is

resolved, and the ensemble command is added that namespace context.

Parent namespaces like "a" and "b" are created automatically, as needed.

.PP

If the \fIensName\fR 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.

.PP

If there are any arguments following \fIensName\fR, then they are

treated as commands, and they are executed to update the ensemble.

The following commands are recognized in this context:  \fBpart\fR

and \fBensemble\fR.

.PP

The \fBpart\fR command defines a new part for the ensemble.

Its syntax is identical to the usual \fBproc\fR command, but

it defines a part within an ensemble, instead of a Tcl command.

If a part called \fIpartName\fR already exists within the ensemble,

then the \fBpart\fR command returns an error.

.PP

The \fBensemble\fR command can be nested inside another \fBensemble\fR

command to define a sub-ensemble.

.SH "WHAT IS AN ENSEMBLE?"

The usual "info" command is a composite command--the command name

\fBinfo\fR must be followed by a sub-command like \fBbody\fR or \fBglobals\fR.

We will refer to a command like \fBinfo\fR as an \fIensemble\fR, and to

sub-commands like \fBbody\fR or \fBglobals\fR as its \fIparts\fR.

.PP

Ensembles can be nested.  For example, the \fBinfo\fR command has

an ensemble \fBinfo namespace\fR within it.  This ensemble has parts

like \fBinfo namespace all\fR and \fBinfo namespace children\fR.

.PP

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 \fBinfo\fR command.

.PP

The ensemble facility manages all of the part names and keeps

track of unique abbreviations.  Normally, you can abbreviate

\fBinfo complete\fR to \fBinfo comp\fR.  But if an extension adds the

part \fBinfo complexity\fR, the minimum abbreviation for \fBinfo complete\fR

becomes \fBinfo complet\fR.

.PP

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 \fBinfo\fR command

is invoked without any arguments, it produces the following error

message:

.CS

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\fR

.CE

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 \fB@error\fR.  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.

.SH 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:

.CS

vwait x

tkwait visibility .top

tkwait window .

.CE

we could use commands with a uniform syntax, like this:

.CS

wait variable x

wait visibility .top

wait window .

.CE

The Tcl package could define the following ensemble:

.CS

ensemble wait part variable {name} {

    uplevel vwait $name

}

.CE

The Tk package could add some options to this ensemble, with a

command like this:

.CS

ensemble wait {

    part visibility {name} {

        tkwait visibility $name

    }

    part window {name} {

        tkwait window $name

    }

}

.CE

Other extensions could add their own parts to the \fBwait\fR command

too.

.SH KEYWORDS

ensemble, part, info