proc(3Tcl)

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.  Whenever
     the new command is invoked, the contents of body will be executed by the
     Tcl interpreter.  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.

     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.  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 don't have defaults, and there must not be
     any extra actual arguments.  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.  Global variables can only be
     accessed by invoking the global command or the upvar command.

     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 doesn't 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.


KEYWORDS
     argument, procedure