J3/04-128

Date:    13 Dec. 2003
To:      J3
From:    Dan Nagle
Subject: LOCAL for non-present optional arguments


The suggestion that optional dummy arguments have a local attribute
allowing them to be used when the corresponding actual argument
is not present has been discussed for some time.  This paper
proposes a scheme for doing so.

Number:

Title: LOCAL for OPTIONAL Dummy Arguments

Submitted By: J3

Status: For Consideration

References:

Basic Functionality: Create a local variable in place of a non-present
                     dummy argument.  Possibly, specify an initial
                     value of the variable

Rationale:  Many uses of optional dummy arguments require that the procedure
            detect the non-presence, and supply a default value to a local
            variable in place of the missing argument's value.  Specifying this
            at a high level seems to have value.

Estimated Impact: This proposal may interfere with current schemes
                  for detecting non-present arguments, and may encourage
                  detection of the default value rather than use
                  of the higher-level present intrinsic.  However, this
                  has been discussed for so long in so many forums,
                  that further consideration is warranted.

Detailed Specification:  LOCAL Attribute of OPTIONAL procedure arguments.

                         LOCAL [ ( i-e ) ]

                         Specifies that when the dummy argument is not present
                         a local variable exists in the procedure with the
                         same name.  The dummy argument must not have
                         INTENT( OUT) if the initial value is specified.
                         The procedure must have an explicit interface,
                         but it needed that for the OPTIONAL part, anyway.

                         If { i-e ) is present, the local variable has
                         the initial value given by the initialization
                         expression.

                         Example:

                         INTEGER, OPTIONAL, LOCAL( -HUGE( FOO)) :: FOO

                         Specifies that if FOO is present, then processing
                         occurs as at present.  If FOO is not present,
                         a local variable named FOO exists and has the initial
                         value -HUGE( FOO).

History: