Provided by: tcl8.5-doc_8.5.19-4_all 
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. Arguments with default values that are
followed by non-defaulted arguments become required arguments. 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 corresponding 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 procedure 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 created 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 command. If the procedure does not 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