proc(n) Tcl Built-In Commands proc(n)______________________________________________________________________________NAMEproc - Create a Tcl procedure
SYNOPSISproc 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. When‐
ever 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. Arguments with default val‐
ues that are followed by non-defaulted arguments become required argu‐
ments. In 8.6 this will be considered an error.
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 cor‐
responding argument in the invoking command or the argument's default
value. Actual arguments are assigned to formal arguments strictly in
order. Arguments with default values need not be specified in a proce‐
dure invocation. However, there must be enough actual arguments for
all the formal arguments that do not have defaults, and there must not
be any extra actual arguments. Arguments with default values that are
followed by non-defaulted arguments become required arguments (in 8.6
it will be considered an error). 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 cre‐
ated for each of the procedure's arguments. Other variables can only
be accessed by invoking one of the global, variable, upvar or namespace
upvar commands.
The proc command returns an empty string. When a procedure is invoked,
the procedure's return value is the value specified in a return com‐
mand. If the procedure does not execute an explicit return, then its
return value is the value of the last command executed in the proce‐
dure'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 ALSOinfo(n), unknown(n)KEYWORDS
argument, procedure
Tclproc(n)
