!DupExit statement: Difference between revisions

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The ''!DUPEXIT'' statement conditionally closes the current procedure, and it continues compilation in the procedure (or command level statement) that INCLUDE'd the current procedure.
The <var>!DUPEXIT</var> statement conditionally closes the current procedure, and it continues compilation in the procedure (or command level statement) that INCLUDE'd the current procedure.


As such, !DUPEXIT is not a valid statement at command level. It conditionally closes
As such, <var>!DUPEXIT</var> is not a valid statement at command level. It conditionally closes
the current procedure if the explicit or implicit macro variable is defined. If the macro
the current procedure if the explicit or implicit macro variable is defined. If the macro
variable is not defined, the variable is set to defined, and processing continues in the
variable is not defined, the variable is set to defined, and processing continues in the
current procedure. !DUPEXIT really performs the work of two macro statements:
current procedure. <var>!DUPEXIT</var> really performs the work of two macro statements:
<var>!IFNDEF</var> and <var>!DEF</var>


!IFNDEF and !DEF.
<var>!DUPEXIT</var> can, optionally, be followed by the name of a macro variable. If the macro
 
!DUPEXIT can, optionally, be followed by the name of a macro variable. If the macro
variable name is not specified, it defaults to the name of the current procedure. In this
variable name is not specified, it defaults to the name of the current procedure. In this
latter case, the length of the procedure name must be less than the setting of the
<b>latter case</b> (i.e., a "naked" <var>!Dupexit</var>), the length of the procedure name must be less than the setting of the
LAUDIT system parameter (unless the parameter is set to 255).
<var>[[LAUDPROC parameter|LAUDPROC]]</VAR> system parameter (unless the parameter is set to 255).
!DUPEXIT can be useful for preventing one-time-only definitions (%variable or
subroutine) from being performed more than once. For example, the !DUPEXIT
statement in the following example prevents subroutine COMMON from being defined
more than once, as long as the subroutine is only defined in procedure COMPLEX:


PROCEDURE COMPLEX
<var>!DUPEXIT</var> can be useful for preventing one-time-only definitions (%variable or
  !DUPEXIT
subroutine) from being performed more than once. For example, the <var>!DUPEXIT</var>
statement in the following example prevents subroutine <code>COMMON</code> from being defined
more than once, as long as the subroutine is only defined in procedure <code>COMPLEX</code>:
<p class="code">PROCEDURE COMPLEX
!DUPEXIT
   SUBROUTINE COMMON(%INPUT IS FLOAT)
   SUBROUTINE COMMON(%INPUT IS FLOAT)
   . . . . . .
   . . .  
   END SUBROUTINE
   END SUBROUTINE
END PROCEDURE
END PROCEDURE </p>


The first time COMPLEX is INCLUDE'd, the !DUPEXIT will not close COMPLEX
The first time <code>COMPLEX</code> is INCLUDE'd, the <code>!DUPEXIT</code> will not close <code>COMPLEX</code>
(because COMPLEX will be undefined), but it will then define COMPLEX. Any
(because <code>COMPLEX</code> will be undefined), but it will then define <code>COMPLEX</code>. Any
subsequent time that COMPLEX is INCLUDE'd, the !DUPEXIT will cause it to be closed
subsequent time that <code>COMPLEX</code> is INCLUDE'd, the <code>!DUPEXIT</code> will cause it to be closed
immediately, because at that point COMPLEX will be defined.
immediately, because at that point <code>COMPLEX</code> will be defined.


If subroutine COMMON might be defined in other procedures, COMPLEX might be
If subroutine <code>COMMON</code> might be defined in other procedures, <code>COMPLEX</code> might be
changed as follows:
changed as follows:
<p class="code">PROCEDURE COMPLEX
!DUPEXIT COMMON
  SUBROUTINE COMMON(%INPUT IS FLOAT)
  . . .
  END SUBROUTINE
END PROCEDURE </p>


PROCEDURE COMPLEX
This tactic will only work as long as other procedures that define subroutine <code>COMMON</code>
!DUPEXIT COMMON
SUBROUTINE COMMON(%INPUT IS FLOAT)
. . . . . .
END SUBROUTINE
END PROCEDURE
 
This tactic will only work as long as other procedures that define subroutine COMMON
also:
also:
<ul>
<ul>
<li>Define it conditionally based on whether COMMON is defined.
<li>Define it conditionally based on whether <code>COMMON</code> is defined. </li>
<li>Define COMMON if they define the subroutine.
<li>Define <code>COMMON</code> if they define the subroutine. </li>
</ul>
</ul>


This can be done with a !DUPEXIT or with a [[!IFNDEF]] and a [[!DEF]].
This can be done with a <var>!DUPEXIT</var> or with a <var>!IFNDEF</var> and a <var>!DEF</var>.


==See also==
==See also==
<ul>
<ul>
<li><var>[[User Language Macro Facility#!IFNDEF var|!IFNDEF]]</var>
<li><var>[[SOUL macro facility#!IFNDEF var|!IFNDEF]]</var> </li>
<li><var>[[User Language Macro Facility#!DEF var|!DEF]]</var>
<li><var>[[SOUL macro facility#!DEF var|!DEF]]</var> </li>
</ul>
</ul>


[[Category:User Language macro facility]]
[[Category:SOUL macro facility]]

Latest revision as of 12:06, 16 July 2019

The !DUPEXIT statement conditionally closes the current procedure, and it continues compilation in the procedure (or command level statement) that INCLUDE'd the current procedure.

As such, !DUPEXIT is not a valid statement at command level. It conditionally closes the current procedure if the explicit or implicit macro variable is defined. If the macro variable is not defined, the variable is set to defined, and processing continues in the current procedure. !DUPEXIT really performs the work of two macro statements: !IFNDEF and !DEF

!DUPEXIT can, optionally, be followed by the name of a macro variable. If the macro variable name is not specified, it defaults to the name of the current procedure. In this latter case (i.e., a "naked" !Dupexit), the length of the procedure name must be less than the setting of the LAUDPROC system parameter (unless the parameter is set to 255).

!DUPEXIT can be useful for preventing one-time-only definitions (%variable or subroutine) from being performed more than once. For example, the !DUPEXIT statement in the following example prevents subroutine COMMON from being defined more than once, as long as the subroutine is only defined in procedure COMPLEX:

PROCEDURE COMPLEX !DUPEXIT SUBROUTINE COMMON(%INPUT IS FLOAT) . . . END SUBROUTINE END PROCEDURE

The first time COMPLEX is INCLUDE'd, the !DUPEXIT will not close COMPLEX (because COMPLEX will be undefined), but it will then define COMPLEX. Any subsequent time that COMPLEX is INCLUDE'd, the !DUPEXIT will cause it to be closed immediately, because at that point COMPLEX will be defined.

If subroutine COMMON might be defined in other procedures, COMPLEX might be changed as follows:

PROCEDURE COMPLEX !DUPEXIT COMMON SUBROUTINE COMMON(%INPUT IS FLOAT) . . . END SUBROUTINE END PROCEDURE

This tactic will only work as long as other procedures that define subroutine COMMON also:

  • Define it conditionally based on whether COMMON is defined.
  • Define COMMON if they define the subroutine.

This can be done with a !DUPEXIT or with a !IFNDEF and a !DEF.

See also

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