Talk:Rexx/Archive 1

Archive 1

Reserved words

Um, how does it have NO reserved words, especially when "DO" is a reserved word as explained in the article? -- Anon

They are reserved only in context (not globally, as in C). So 'DO' is fine as a variable name, for example. NetRexx takes this further -- keywords are not reserved anywhere, even in context. This means that new keywords can be added to the language at any time, without breaking existing programs. mfc

This works quite well; /**/

say=4;end = 2; do=say+end; do me=end to do; say say + me; end

The result is to print a list of numbers from 6 to 10 (ie say+end to say+do). This is under regina.rexx v 3.3 (which emulates ANSI + a few extensions of OS/2 and Amiga heritage. --Wendy.krieger 08:27, 28 October 2007 (UTC)

Starting comment

I think that the /* */ start is only required in OS/2 .CMDs. I guess that in Unix the required start is #!/bin/regina or something similar. -- Error

It's required in ARexx, so it's not only OS/2.212.85.68.44 11:59, 19 September 2007 (UTC)

ah, didn't know. Will check with the REXX gurus. -- Viajero 09:03 30 Jun 2003 (UTC)

The "/* ..." is required in VM/CMS (called z/VM these days). VM/CMS systems check the first line of the file to determine which "executor" should be invoked to process the file.

A first line beginning with "&TRACE" triggers the EXEC2 executor, and a first line with with neither &TRACE nor /* at its start drops through to the original EXEC procesor (a sort of BAT precursor). However, if evoked explictity as a macro, etc., the REXX interpreter does not require that the first line start with /*.

I can't speak to the OS/2 question, although I can say that Rexx started on VM and that this mechanism is predates the release of Rexx to the VM sites outside IBM. -- RossPatterson 15:53, 26 Sep 2004 (UTC)

Unix systems require a "#!<something_or_other>" to identify the program that executes the script. In the Regina case, this is typically /usr/bin/rexx, just as in the Perl case it is often /usr/bin/perl. The usage is ancient - shell scripts have begun with "#!/bin/sh" for around 30 years. As to "/* ... */" in Unix, Regina does not require it and neither does Unix. -- RossPatterson 15:53, 26 Sep 2004 (UTC)

(i think its #! /usr/bin/regina)

—Preceding unsigned comment added by 24.51.17.71 (talk • contribs) 21:21, 10 February 2006

Yes, #!/usr/bin/regina will work, if you happen to have Regina installed in /usr/bin (so will /usr/bin/rexx - Regina installs both). But that's a Unix-ism (the whole #!/path/to/interpreter/executable thing), and Regina doesn't require it - you can run a Rexx program simply by typing rexx filename, event if it doesn't have the "sh-bang" line. RossPatterson 02:28, 11 February 2006 (UTC)

Object Rexx [oorexx.org] also allows the "sh-bang" first line. The executable name used by oorexx is rexx, therefore #!/usr/bin/rexx would work. CheyenneWills 20:12, 17 February 2006 (UTC)

I'm pretty sure (although I can't test it) that VM/CMS requires a starting comment only in some circumstances. You can write a Rexx program with no comments at all, compile it, and run it with no problems. I think you can also call a Rexx program without a starting comment from another Rexx program. Therefore, it's not technically a requirement of the language, but of a specific execution environment on the platform, (The "EXEC PROCESSOR") and more because of a historical "accident" than anything else. Had IBM allowed a file type of REXX, it would not have been an issue. Presumably, the rationale was that people would want to rewrite existing EXEC2 macros in REXX and use the same filename and type, so the requirement for interpreted versions was necessary. --Hagrinas 18:05, 27 June 2007 (UTC)

Exactly correct. mfc 17:26, 19 September 2007 (UTC)

The first line of an OS390 rexx script must be /* rexx ..... */. This informs the TSO interpreter that it is REXX and not a CLIST.

Rexx by itself, under Windows or OS/2 does not require a comment at the beginning of the code. This is used by the default command processor to pass commands to the rexx processor. For example, one could create a file with the single line in it:

parse source s; parse version v; say s v

returns WIN32 COMMAND D:\cdata\test.me REXX-Regina_3.3(MT) 5.00 25 Apr 2004

If this is run, eg by invoking the rexx processor, eg regina test.me, then it works as expected. You can also invoke rexx lines inside 4nt or tcmd by @rexx[], as shown below:

The line echo %@rexx[parse source s; parse version v; return s v]

returns WIN32 SUBROUTINE parse REXX-Regina_3.3(MT) 5.00 25 Apr 2004

None the same, the rexx invoked in this way runs in a different shell to that invoked by the command processor by /* rexx */, in as much that it does not have access to the launching process's environment etc. For example, the 4nt command of thhe form set zm=%@rexx[return reverse(value(zm,,SYSTEM))] replaces zm by its string-reverse, using the rexx interpreter to do this. --Wendy.krieger 08:12, 28 October 2007 (UTC)

The /* comment */ is required in TSO/E; further, when the procedure comes from SYSPROC the it must start specifically with /* REXX */.

Would it be appropriate to add a link to IBM (April 19, 1988). "Announcement Letter Number 288-191 IBM TSO EXTENSIONS VERSION 2". Announcement Letters, {{cite web}}: Cite has empty unknown parameters: |trans_title=, |month=, and |coauthors= (help); Unknown parameter |separator= ignored (help) the IBM announcement for REXX support in TSO/E Version 2? Shmuel (Seymour J.) Metz Username:Chatul (talk) 18:57, 31 August 2010 (UTC)

Compound variables

This new section replacing the former "Arrays" is much better, thanks. It's a bit long, and I'd prefer to kill the first of the two "dictionary" examples. The 2nd example is compact and documents when it will fail. The 1st example is limited to the REXX concept of words, and ANSI REXX managed to FUBAR this simple concept. -- Omniplex 08:13, 27 June 2006 (UTC)
P.S.: Of course we can just use a separate stem enumeration of defined tails instead of a string of blank (or ANSI else) separated words if necessary, but the more interesting case is to mix it as in the second example.

My reading of this section makes me think that compound variables are more like Java Maps than Vectors. -- ABala 62.189.157.240 15:32, 27 April 2007 (UTC)

More like a Hashtable, although there isn't really any construct in Java (or most other languages) that is a direct equivalent to a collection of Rexx compound variables. Much of the richness comes from the ability to construct tails as if they were additional subscripts of an array or subelements of a hashtable, even though the tail is actually the entire key. RossPatterson 22:14, 27 April 2007 (UTC)

REXX compound variables form one of the stumbling blocks if one comes from an Algol-based system, like C. REXX does not actually do anything more than variable replacement, so if CITY=BRISBANE, then POPULATION.CITY returns POPULATION.BRISBANE. It has no useful way of evaluating the sub-string at access time. If you want a(z+1)=2*a(z), you must do "z1=z+1; a.z1=2*a". Generally, when i want to use a compound string indirectly, i always do it indirectly, ie "z1=0; a.z1=...", rather than "a.0=...". --Wendy.krieger 08:34, 28 October 2007 (UTC)

Loop constructs

Another, occasionally handy loop construct:

  do 20
    [instructions]
  end

That will simply run the loop 20 times, without any tracking variable.212.85.68.44 11:59, 19 September 2007 (UTC)

Does the do until loop not check if the condition is met before the first iteration, i.e. shouldn't the expansion

  do forever
    [instructions]
    if [condition] then leave 
  end

be enclosed into a if [not condition] do ... end? (I'm just curious, I don't know REXX). 84.150.122.29 21:02, 19 January 2007 (UTC)

Yes, a do until loop checks the condition at the bottom of the loop, so it is exactly equivalent to the code you entered above. If you want a test at the top of the loop, you use do while instead. As Cowlishaw's book says,

Example:
   do i=1 to 10 by 2 until i>6
     say i
     end
   /* Would display: 1, 3, 5, 7 */

RossPatterson 21:13, 20 January 2007 (UTC)

Thanks, I had somehow not noticed that testing before the loop, and then again at the bottom during every iteration amounts to the same as testing at the top (well, add a caveat about values of induction variables etc.) 84.150.104.35 19:38, 22 January 2007 (UTC)

I'm no REXXpert, but I think there's a mistake in the article. I would expect "do while [condition]" to be equivalent to "do until [not condition]". I would expect both of those forms to test [condition] before each iteration of [instructions], which would mean that they are not equivalent to the form

  do forever
    [instructions]
    if [condition] then leave 
  end

which looks like it tests [condition] after each iteration. Would anyone care to disagree, or tell me that I should edit the article? ⫷ SkiSkywalker ⫸ (talk) 23:36, 24 April 2012 (UTC)

Nope, do while tests at the top of the loop, and do until at the bottom, just like the article says. That's typical for those constructs, in every language that has them. RossPatterson (talk) 01:42, 25 April 2012 (UTC)

function packages

Shouldn't the article mention the necessity of third party libraries, for additional functions, and to interface with specific OS services and software? I guess that should be in the Features section; i see a brief mention in the paragraph on the Interpret verb. I'm not adding it myself because at present i can't find the right wording, and am not quite sure of how to not make a mistake. Moreover, perhaps it is considered evident, that a programming language limit itself to only general logic processing?

Some buzzwords/articles to point to:

• binding (computer science)
• Language binding
• Scope (programming)

--Jerome Potts 23:19, 21 July 2007 (UTC)

III of Orlando, Florida created a couple of rxLib packages for VM/CMS, but I don't know if they are still available. At the very least III offered an extended math and an extended string package. I can't recall, but they might have had I/O libs as well.

As a side note, III enhanced Rexx with assembler to create an Object-oriented programming system development environment, which provided primitive windowing under CMS.

--UnicornTapestry (talk) 02:05, 8 November 2008 (UTC)

Updating of variables by host commands

I remember that, on VM/CMS, not all external host commands would be able to set Rexx variables, there was some kind of requirement, but i don't remember the terminology for the mechanism. Does anyone know, and if so, is it something which could/should be present in this article? And i don't know whether this was an issue with the later implementations of Rexx, on other OSes.

--Jerome Potts 23:28, 21 July 2007 (UTC)

• REXX variables are accessed by the EXECCOMM interface on VM. On a related note, I'm puzzled by the statement that VALUE()'s "main purpose is to read and set environment variables." VALUE() was around as a way to resolve symbols for years before arguments were added to allow it to set and retrieve external variables. Not R (talk) 21:54, 28 January 2008 (UTC)

Basic?

One of the boxes mentiones Rexx was influenced by PL/I, EXEC II, and Basic.

I can see PL/I and even ALGOL for syntax and EXEC II in regard to internals. I could even imagine an argument for SNOBOL. But it's beyond me what BASIC has to do with it. Does anyone know why Basic is mentioned?

--UnicornTapestry (talk) 01:52, 8 November 2008 (UTC)

Perhaps (a) interpretive and (b) typeless Tedickey (talk) 12:23, 8 November 2008 (UTC)

I would argue that the similarity with BASIC is its ease of initial learning and suitability for tyros. Gomberg (talk) 21:02, 6 March 2009 (UTC)

Basic was a strong influence .. several of the built-in functions come from Basic (RANDOM was originally called RND, for example), and much of the ease-of-use features (no declarations, just one type of number, etc.). Indeed, Thomas Kurtz (one of the original authors of Basic) wrote:

"Regarding variable types, we felt that a distinction between 'fixed' and 'floating' was less justified in 1964 than earlier ... to our potential audience the distinction between an integer number and a non-integer number would seem esoteric. A number is a number is a number."

Too bad most language designers don't bother to read about older languages. mfc (talk) 11:42, 10 March 2009 (UTC)

Syntax

Currently, this article has way too much content in the Syntax section. It should just give one or two brief examples, but instead it takes up more than half the article; it needs to be shortened down, a lot. See WP:NOT, Wikipedia is not a manual or tutorial of any kind. Thanks. — ^FatalError 03:03, 6 January 2009 (UTC)

On an unrelated subject, and just style, in the interpret example, (4) should be replaced by 4. The parens do no harm in this particular case, but it looks a bit odd to use them with a space after the routine name. Gomberg (talk) 21:00, 6 March 2009 (UTC)

Normally I wouldn't argue with someone with so much Rexx background, but if we're talking about "interpret 'say' X || '(4) ; exit'", doesn't that become "interpret say SQUARE(4); exit", hence a function call, rather than "interpret say SQUARE 4; exit", which wouldn't be a call? RossPatterson (talk) 02:16, 7 March 2009 (UTC)

While I don't agree that the Syntax section is either too long or a tutorial, I find it badly organized. There is a lot of information under individual statements that is either extraneous, belongs in the lead-in for the statement or belongs elsewhere entirely. 208.103.155.149 (talk) 16:01, 31 December 2010 (UTC)

NetRexx is not Rexx

NetRexx is a separate language, with its own syntax, although it is certainly inspired be Rexx. Shmuel (Seymour J.) Metz Username:Chatul (talk) 18:19, 31 August 2010 (UTC)