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

Tcl                                                                                                   proc(3tcl)