proc(n) Tcl proc(n)
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NAME
proc - Create a Tcl procedure
SYNOPSIS
proc name args body
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DESCRIPTION
The proc command creates a new Tcl procedure named name,
replacing any existing command or procedure there may have
been by that name. Whenever the new command is invoked, the
contents of body will be executed by the Tcl interpreter.
Normally, name is unqualified (does not include the names of
any containing namespaces), and the new procedure is created
in the current namespace. If name includes any namespace
qualifiers, the procedure is created in the specified
namespace. Args specifies the formal arguments to the
procedure. It consists of a list, possibly empty, each of
whose elements specifies one argument. Each argument
specifier is also a list with either one or two fields. If
there is only a single field in the specifier then it is the
name of the argument; if there are two fields, then the
first is the argument name and the second is its default
value.
When name is invoked a local variable will be created for
each of the formal arguments to the procedure; its value
will be the value of corresponding argument in the invoking
command or the argument's default value. Arguments with
default values need not be specified in a procedure
invocation. However, there must be enough actual arguments
for all the formal arguments that don't have defaults, and
there must not be any extra actual arguments. There is one
special case to permit procedures with variable numbers of
arguments. If the last formal argument has the name args,
then a call to the procedure may contain more actual
arguments than the procedure has formals. In this case, all
of the actual arguments starting at the one that would be
assigned to args are combined into a list (as if the list
command had been used); this combined value is assigned to
the local variable args.
When body is being executed, variable names normally refer
to local variables, which are created automatically when
referenced and deleted when the procedure returns. One
local variable is automatically created for each of the
procedure's arguments. Global variables can only be
accessed by invoking the global command or the upvar
command. Namespace variables can only be accessed by
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proc(n) Tcl proc(n)
invoking the variable command or the upvar command.
The proc command returns an empty string. When a procedure
is invoked, the procedure's return value is the value
specified in a return command. If the procedure doesn't
execute an explicit return, then its return value is the
value of the last command executed in the procedure's body.
If an error occurs while executing the procedure body, then
the procedure-as-a-whole will return that same error.
KEYWORDS
argument, procedure
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