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



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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 proce-dure; procedure;
       dure; 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 pro-cedures procedures
       cedures 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 automat-ically automatically
       ically created for each of the procedure's arguments.  Other variables can only be accessed by invok-ing invoking
       ing 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 vari-able variable
       able 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)