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proc(n)			     Tcl Built-In Commands		       proc(n)

______________________________________________________________________________

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.	 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 formal arguments.  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  current namespace when body is executed will be
       the namespace that the procedure's name exists in, which	 will  be  the
       namespace  that	it  was	 created  in  unless  it has been changed with
       rename.

       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 ALSO
       info(n), unknown(n)

KEYWORDS
       argument, procedure

Tcl								       proc(n)
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