PL/I preprocessor: Difference between revisions

Revision as of 17:23, 13 October 2013

Revision as of 22:40, 11 November 2013

Line 55:

===Preprocessor procedures===

A preprocessor procedure is a [[subroutine]] executed by the preprocessor. The procedure is delimited by <code>%PROCEDURE</code> and <code>%END</code> statements and can contain only preprocessor statements, without the leading '%'. It is invoked as a function reference from ''open code'', outside of any preprocessor procedure, or from another preprocessor procedure, and returns a CHARACTER or FIXED value. When the procedure is invoked from open code the arguments are passed ''by name'', that is they are interpreted as character strings delimited by commas or a right parenthesis, all leading, trailing, or imbedded blanks are significant and considered part of the argument.<ref name=ibm3lr40>{{cite book|last=IBM Corporation|title=Enterprise PL/I for z/OS PL/I for AIX WebSphere Developer for zSeries PL/I for Windows Language Reference|year=2005|url=http://pic.dhe.ibm.com/infocenter/pdthelp/v1r1/topic/com.ibm.entpli.doc_3.5/ibm3lr40.pdf}}</ref>{{rp|pp.508–509508-509}}

==Preprocessor builtins==

These are the builtins for IBM's ''PL/I for MVS and VM'' compiler.<ref name=PLI1.1>{{cite book|last=IBM Corporation|title=IBM PL/I for MVS & VM Language Reference|year=1995}}</ref>{{rp|pp.404–406404-406}} There can be considerable difference between preprocessors of various PL/I compiler in the builtins provided.

* '''COMPILETIME''' &mdash; returns the date and time of compilation as a character string such as "15 SEP 12 15:30:00" for September 15, 2012 3:30PM (local time).

* '''COUNTER''' &mdash; returns a character string containing a number that is "00001" for the first call to COUNTER and increases by one for each subsequent call.

Line 107:

==Evolution==

A '''1964''' report on "NPL"<ref>{{cite book|last=IBM Corporation|title=NPL Technical Report|year=1964|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/pli/320-0908_NPL_Technical_Report_Dec64.pdf}}</ref>{{rp|pp.109–114109-114}}, as PL/I was called at the time, provided that macro procedures, identified by the keyword ''MACRO'', could use the complete facilities of the language. The following compile-time statements were allowed in open code:

* <code>%DECLARE</code> &ndash; both fixed-length and varying character strings were defined.

* ''%assignment''

Line 116:

"NPL" as defined in this manual was never implemented.

In '''1965''' an update to IBM's ''PL/I Language specification'' defined an even less ambitious preprocessor language<ref>{{cite book|last=IBM Corporation|title=IBM Operating System/360 PL/I: Language Specifications (C28-6571-1)|year=1965|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/pli/C28-6571-1_PL_I_Language_Specifications_Jul65.pdf}}</ref>{{rp|pp.131–133131-133}}. All mention of preprocessor preprocessor procedures was omitted. The following compile-time statements were specified:

* <code>%DECLARE</code>

* ''%assignment''

Line 123:

* <code>%GOTO</code>

This language specification was again never implemented, however a '''1966''' revision of this manual restored preprocessor procedures with the now-current <code>%PROCEDURE ...%END</code> syntax and brought the specification close to what was actually included in PL/I(F)<ref>{{cite book|last=IBM Corporation|title=IBM Operating System/360 PL/I: Language Specifications (C28-6571-3)|year=1966|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/pli/C28-6571-3_PL_I_Language_Specifications_Jul66.pdf}}</ref>{{rp|pp.132–139132-139}}<ref>{{cite book|last=IBM Corporation|title=IBM System/360 PL/I Reference Manual (C28-8201-3)|year=1969|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/pli/C28-8201-1_PLIrefMan_Jan69.pdf}}</ref>{{rp|pp.154–162154-162}}. Fixed-length character variables were gone. New statements added were:

* <code>%ACTIVATE</code>

* <code>%DEACTIVATE</code>