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 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 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 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 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