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.  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

Tcl                                                                                                   proc(3tcl)