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







proc - Create a Tcl procedure








proc name args body












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.








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}]
}












info(n), unknown(n)










argument, procedure







  

    
    Tcl