PL/I preprocessor: Difference between revisions

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==Example==

The following example for IBM PL/I for OS/2 illustrates the use of a preprocessor procedure to implement a C-like write statement for PL/I.<ref>{{cite web|last=Sturm|first=Eberhard|title=UIO-Makros für Builtin-Funktionen fileread und filewrite|url=httphttps://www.uni-muenster.de/ZIV.EberhardSturm/uio.cpy|accessdateaccess-date=January 22, 2012}}</ref> The procedure would be called by coding the statement {{code|uwrite file(filename) from(varying_string) count(byte_count);}} {{mono|<var>Byte_count</var>}} is optional and defaults to the length of {{mono|<var>varying_string</var>}} if omitted.

<syntaxhighlight lang="rexx" line highlight="1,25,26">

<pre>

%uwrite:

procedure keys (File, From, Count);

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%end;

%act uwrite;

</syntaxhighlight>

</pre>

The statement {{code|uwrite file(file_name) from(var_str) count(64);}} generates the following:

<syntaxhighlight lang="rexx">

<pre>

do;

dcl Count00001 fixed bin (15);

Count00001 = filewrite(file_name, ptradd(addr(var_str), 2), min(length(var_str), 64));

end;

</syntaxhighlight>

</pre>

==Evolution==

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* <code>%<var>assignment</var></code>

* <code>%<var>null statement</var></code>

* <code>%IF <var>compile_time_comparison</var> THEN <var>unit</var> [ELSE <var>unit</var>]</code> &ndash; this causes one or the other <var>unit</var> to be included in the source.

* <code>%GOTO</code>

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* <code>%<var>assignment</var></code>

* <code>%<var>null statement</var></code>

* <code>%IF <var>compile_time_comparison</var> THEN GOTO <var>label</var></code> &ndash; No <code>ELSE</code> clause was defined.

* <code>%GOTO</code>

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* <code>RETURN</code> in a compile-time procedure only.

* <code>%INCLUDE</code>

* <code>&%IF</code> &ndash; the <code>%IF <var>compile_time_comparison</var> %THEN <var>unit</var> [%ELSE <var>unit</var>]</code> was restored.

A single compile-time builtin, <code>SUBSTR</code>, was added.

Also in 1966 Robert Rosin published a pair of articles<ref>{{cite journal|last=Rosin|first=Robert|title=PL/I Macro Processor - Progress Report|journal=PL/I Bulletin|date=August 1966|issue=2|url=http://www.iron-spring.com/PLI_Bulletins/PLI_Bulletin_2.pdf|accessdateaccess-date=January 22, 2013}}</ref><ref>{{cite journal|last=Rosin|first=Robert|title=Macros in PL/I|journal=PL/I Bulletin|date=August 1966|issue=2|url=http://www.iron-spring.com/PLI_Bulletins/PLI_Bulletin_2.pdf|accessdateaccess-date=January 22, 2013}}</ref> discussing development of the preprocessor. This development was based in a "[[SHARE (computing)|SHARE]] XXVI Memo" from earlier the same year and a paper by Mark Elson. Rosin credits [[MAD (programming language)|MAD]] as the only previous example of a macro processor in a high-level language.

==See also==

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==External links==

*{{cite web

|url = http://publibfp.boulder.ibm.com/cgi-binepubs/bookmgr/BOOKSpdf/ibm3lr80/21.0?DT=20091014225516pdf

|title = Enterprise PL/I Language Reference (SC27-1460-09): Chapter 21. Preprocessor Facilities

|author = IBM Corporation

|date = October 2009

|accessdateaccess-date = Jan 19, 2012

}}

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|author = Micro Focus International plc

|year = 2011

|accessdateaccess-date = Feb 14, 2012

}}

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|author = Kednos Enterprises

|year = 2007

|accessdateaccess-date = Feb 14, 2012

}}

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|author = Peter Flass

| year = 2010

|access-date = 2017-12-06

|accessdate = July 2014

}} Comparison of preprocessor features