NAME¶
proc - Create a Tcl procedure
SYNOPSIS¶
proc name args body
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 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.
EXAMPLES¶
This is a procedure that accepts arbitrarily many arguments and prints them out,
one by one.
proc printArguments args {
foreach arg $args {
puts $arg
}
}
This procedure is a bit like the
incr command, except it multiplies the
contents of the named variable by the value, which defaults to
2:
proc mult {varName {multiplier 2}} {
upvar 1 $varName var
set var [expr {$var * $multiplier}]
}
SEE ALSO¶
info(3tcl), unknown(3tcl)
KEYWORDS¶
argument, procedure