Talk:PL/I

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[edit] Early discussions

I deleted the following, which is not true:

The original IBM mainframes used the same symbol 'I' for both the letter 'I' and the number '1'. Thus, the way that it is commonly written and normally spelled are different.

IBM mainframes used separate symbols for the letter and the number. The 'I' in PL/I is a roman numeral. -- Simon J Kissane

Thank you. That's what I thought, too, but wasn't sure enough about 3 decade old memories to make the change. --Buz Cory
I did more research and I hope this clarifies what I meant to say:

I was trying to make a distinction between the character and the font. Unfortunately, I used the wrong symbols. It was the small "L" and the number "1" that used to identical font symbol (i.e., l and 1 look the same - more or less - even though I typed the "el" character first, and the "one" character second).

I was not intending to say that the characters were identical (i.e., had identical values in EBCDIC), merely that they looked the same. This was true for the Courier font ball used in IBM Selectrics, which were also used as operator terminals in some S/360 installations, and the font symbols may have been identical in the print cylinder in the 1403 printer. Because I don't have the original context - or don't know how to get my original contribution for the context, I'm not sure why I even brought up the character confusion thing...

Cheers --17:29, 31 December 2006 (UTC)RSzoc

The bit about SABRE is from personal experience. I was offered (and turned down) a position with the SABRE project ca 1965. Don't know if they stayed w/ PL/I or changed to a different language.

The (military/aerospace) project I was on at the time would have used PL/I if it had been useable early enough. We went through major contortions to do a real-time/multi-tasking system requiring dynamic allocation of records (structs to you C weenies) in FORTRAN IV. Further, FORTRAN required 512K of RAM to compile, the PL/I compiler would work in 128K. --Buz Cory

Evidently, the SABRE folks didn't get a really solid PL/I compiler for their platform until the early 1970s. They may have wanted to use PL/I earlier than that, but I can vouch that at least the portions of the system that American Airlines dealt with were almost entirely 7090 assembler before the early 1970s. (Working off my father's notes on this one; he wrote the compiler, so there's a chance his history is biased, of course.) --Cliff Biffle

Not so sure about that "case insensitive" part. At that time virtually all work was done entirely in upper case due to hardware limitations. --Buz Cory

Nice job on the history. Some references to written documents (which I understand may not exist) would be nice. If its personal experience, then say so. --drj

----
The parts of the history that I wrote are personal experience. If one can find copies of Datamation from ca 1965, the arguments that I mentioned about not using PL/1 are in there. The part about NELIAC is from a book I read ca 1962 whose name and author I cannot recall.
The part above about system requirements for FORTRAN and PL/1 is also personal recall. --Buz Cory

Most of the history stuff I added is purely from memory. I read it somewhere. I wasn't even alive when PL/I was being developed. -- Simon J Kissane

A couple of inaccuracies in the "Retrospective section".

First, it states that the "user wouldn't know whether a statement was a declaration or a executable statement until one saw the period at the end. " The truth is that PL/I uses (and has always used) the semi-colon as a statement terminator. COBOL is that language that used periods. Additionally, a declaration statement ALWAYS begins with the keyword "DECLARE" or "DCL", so it's easy to figure out what kind of statement it is. Also, "format free" languages that could be spread along a number of lines before being terminated had been around since at least the early 1960/61 if not earlier. Even assembly language could span multiple lines if one put a "continuation" character in Column 72 of the "card".

Second, the article states that "the decision to make spaces unimportant, as in Fortran" (I paraphrase) is simply not true. In Fortran, spaces were truly irrelevant. Thus, one could write an "do statement" as follows:

    DO I = 1, 10
        or
    DOI=1,10

Both were considered to be the same (this is the Fortran for the time of the late 60's early 70's).

In PL/I spaces did matter. Taking the same example above:

      DO I = 1 to 100;
          OR
      DOI=1 to 100;

are very different statements; I think the second one won't even compile.

Perhaps you are thinking of Keywords. Like all languages, PL/I has keywords, (such as DECLARE, DO, IF, END, and so on), but, because PL/I had so many keywords, the language designers decided that none of them were to be RESERVED. Going to the Fortran example above, the word DO is a keyword AND is reserved, and cannot be used for any other purpose but in a DO statement. In PL/I, one can use DO in a do statement and also as a variable. The "headache" in writing a PL/I compiler was the requirement that it had to figure out from the context whether a word was being used as a keyword or not.

The example that I remember from back in the day was this. The following is a perfectly valid PL/I statement (because no keywords are reserved):

    IF IF = EQUALS THEN
         THEN = ELSE;
    ELSE ELSE = IF;

Cheers RSzoc 01:02, 26 November 2006 (UTC)

[edit] Year developed

Is 1964 the year PL/1 was first developed? Same as System/360? -- sabre23t 02:17, 19 Sep 2004 (UTC)

I added to the article that PL/I was used at MIT in 1964, which was the oldest reference that I could find. Morris 23:02, Apr 12, 2005 (UTC)
See Fernando J. Corbató#Further reading for the PL/I As a Tool for System Programming reference, which probably gives a lot of detail on this. Might we worth including that as a reference here too. Noel (talk) 18:55, 13 Apr 2005 (UTC)

The PL/I language specification was still being developed in 1964, and there was no PL/I compiler available from IBM when S/360 and OS/360 were released. Documentation for S/360 and OS/360 was available in 1964, but the first systems - at the lower end - did not begin shipping till 1965. My personal recollection is that IBM's production of system 360s didn't begin in high volume until 1968 or so. RSzoc 01:08, 26 November 2006 (UTC)

As for Multics and MIT, the web site of http://www.multicians.org/pl1-raf.html states that "Multics PL/I" was based on an IBM language spec that was not available until 1968. Again, I believe the difference is the time difference between when specifications are made (e.g., 1965 in the case of Multics) and when a final software product containing that specification is actually produced. The above referenced Web site states that the Multics PL/I compiler was developed in 18 months. If we take March, 1968 as the starting point - when the PL/I language spec used by MIT was available, and add 18 months, we get September 1969 as when Multics Pl/I compiler was actually available. MPearl - what is your reference for the 1964 date??RSzoc 01:08, 26 November 2006 (UTC)

As an aside, UNIX was named as a form of word play for Multics. Because the Multics OS was so big - many computer types felt at the time - Dennis Ritchie and Ken Thompson at Bell Labs named their OS Unix, implying small and lean.

Now, of course, all OSes are pretty much out of control, with nothing begin small and lean, except for maybe whatever drives microwave ovens (that last sentence is an editorial comment by me - feel free to snip it out)... RSzoc 18:52, 18 November 2006 (UTC)

[edit] Subpage

Perhaps this isn't really important, but this article is actually a subpage: the subpage "I" of the article "PL". This obviously isn't the intention, but it seems to work alright. Deco 00:37, 17 Nov 2004 (UTC)

[edit] PL/I newsletter

Perhaps a link to the current (Jan 2005) PLI newsletter would be useful? [1] --ClemMcGann 00:50, 20 Mar 2005 (UTC)

[edit] PL/I and C

This page contains the claim (in the "External links" section) that "The C programming language was heavily modelled after PL/I". Alas, this is untrue. The C Progamming Language (by Ritchie, Johnson, Lesk and Kernighan, 1977) says that "Many of its most important ideas stem from ... BCPL", and there is no mention of PL/I. As for BCPL, the BCPL Reference Manual (by Richards, Evans and Maybee, 1974) says that "BCPL is related to CPL", and again no mention of PL/I. (The CPL documents cited date from 1963/65, making it impossible for CPL to have been influenced by PL/I.) So I am going to remove that claim. Noel (talk) 22:20, 12 Apr 2005 (UTC)

[edit] Lost text?

A large block of text was lost here during a spam/vandalism spree earlier this year. Assuming that this removal was an error, I have added it back, and done some copyediting to remove duplicate material that was added after that piece was lost; I also attempted to organize the material a bit better. Noel (talk) 19:40, 13 Apr 2005 (UTC)

[edit] IBM System/360

I know it's nitpicking, but IBM didn't refer to System/360 as the System/360. It was just System/360. My reference is a 1964 copy of the IBM Systems Journal where the entire architecture of the machine was described in Iverson notation. Shoaler 5 July 2005 17:22 (UTC)

[edit] "powerful" vs "ambitious"

I think I disagree with the revert done to my change of the adjective "powerful" to "ambitious." I appreciate the differences between PL/1 and C, but both are NP-complete languages, and I think the use of the word "powerful" in this context is misleading; it gives a false impression, and is (in my opinion) a bit too cheerleading of a word to lead off an article with.

I prefer "ambitious" because it more accurately captures the scope of PL/1 as a featureful language, without reference to the perceived "power" of the language (which really, could mean anything).

Thoughts? I'm also open to other suggestions. As a test, I've changed powerful to "feature-rich", which I think also captures the true nature of the distinction.Nandesuka 15:27, 15 July 2005 (UTC)

I like "feature-rich" (or maybe some other more grammatically correct adjective with the same meaning). I think that "powerful" is too vague with regards to a programming language. JYolkowski // talk 21:30, 15 July 2005 (UTC)
The words “power” and “powerful” have long been associated with PLI. (Remember the Black Panther logo). You can achieve a great deal in a single PLI statement. Just as other languages can claim flexibility, portability, ease-of-use, easy-to-learn, and so on.
A possible issue with “feature rich” is that it could refer to graphics or other features absent in PLI
Perhaps “powerful” should be explained and an example given.
(speaking of examples, I’m removing the hello world with the infinite loop)--ClemMcGann 23:27, 15 July 2005 (UTC)

[edit] Was PL/I the first commercial language to compile itself?

The article reads: PL/I was probably the first commercial language where the compiler was written in the language to be compiled.

(moved posts from talk pages here) -- ClemMcGann 01:08, 6 August 2005 (UTC)
I am of the opinion that Burrough's Algol was before PL/I (compiler written in its own language)
(and Burrough's PLI for the B6700 was written in Algol)
--ClemMcGann 13:13, 5 August 2005 (UTC)

First off, thank you for getting back to me. I guess the easiest way to bring up concerns about factual information like that is to bring it up in the discussion pages, but the way you removed the line without a clear comment did make it impossible to know that you were doing so to dispute the timeline.

I suppose that some of this is my fault for confusing two languages. I could have corrected the error when I first saw it. I actually had a counter-example from NELIAC, which was first publicly announced in 1958, based on publications from the Naval Research Laboratory. What year was the compiler that you were refering to written?

This was discussed last year on alt.folklore.computers, have a look at [2] and seach for the string "Suspect Algol on Burroughs mainframes might have compiled itself first" Or go to message 164 - regards --ClemMcGann 16:21, 5 August 2005 (UTC)

[edit] References

  • Huskey, H. D., Halstead, M. H., and McArthur, R., "NELIAC- A Dialect of ALGOL" in ACM/ CACM 3(08) August 1960
  • JOHNSEN, R. L. JR. Implementation of NELIAC for the IBM 704 and IBM 709 computers. NEL Tech. Mere. No. 428, Sept. 1960.
  • HOPL entry for NELIAC which is the source of the following quote:
Significant in that it provided the first ever bootstrap implementation, and the standard reference for NELIAC (Halstead's book) was for many years the primary reference for such compilers.
Ok, I just re-read what I wrote on PL/I. It's odd that you deleted what you did, since your delete did not argue the point specifically. That is, you removed one of three sentences in that paragraph, the only one that did not claim PL/I was the first commercial (and this is a key point) language designed this way.
That said, I think the idea here is that BALGOL was a research language used in commercial settings, much like C was at first. PL/I was designed to be a commercial language. At least that's how I read it from the source I got that from. Now, of course, I can't find that source. Stupid me, I should have put it in the article, but not being a PL/I guy, I just assumed that it was common knowledge.
Easy things first: do you dispute the dates involed? E.g. do you dispute that NELIAC came before BALGOL or that PL/I came (about 8 years) after both of them? Of not, then I think we can move on too the question of if PL/I can claim to be the first commercial bootstrapped language, no? -Harmil 22:57, 5 August 2005 (UTC)
I only expressed a doubt, not a certainty.
That doubt was based on comments made last year in alt.folklore.computers, It was a long thread.
The claim “Suspect Algol on Burroughs mainframes might have compiled itself first and done it very well.” Is here [3]
A reply “Multics PL/I was written in PL/I, though it was bootstrapped via a temporary compiler (EPL) not written in PL/I.” [4]
I do not dispute that “NELIAC came before BALGOL or that PL/I came (about 8 years) after both of them?”
Actually I don't dispute anything, I just expressed a doubt.--ClemMcGann 01:08, 6 August 2005 (UTC)

[edit] =====

The first commercial version of the PL/I compiler by IBM was the (F) level compiler. In those days, IBM identified many of its software development/system applications with the letters E, F, G, and H. Each letter specified the minimum S/360 memory configuration needed to run that software. The memory configurations for the different letters were:

          Level E:   32KB
          Level F:   64KB
          Level G:  128KB
          Level H:  256KB

(Source: IBM System/360 Operating System Introduction Release 21, IBM Publication number GC28-6534-3 avaiable from www.bitsavers.org).

Thus the PL/I (F) level compiler needed a minimum of 44KB to run(Source: IBM System/360 Operating System, PL/I (F) Compiler Program Logic Manual, IBM Publication Number Y18-6800-3, available from www.bitsavers.org).

For comparison purposes, when I run Microsoft's Outlook in Windows XP, it takes up about 14,604KB to sit there waiting for email to come in. This is about 331 times (33,100%) more memory) that the first IBM PL/I compiler.

I also have the code for that first compiler, (available for a small fee to cover cost of media from cbttape.org) and it is most definitely in assembly language. The PL/I (F) compiler is comprised of about 270 source files and about 385,000 lines of IBM assembly language code. This figure does not include code for the libraries, built-in functions, I/O functions and all that.

Now perhaps the PL/I Optimizing Compiler was written in PL/I but I doubt it very much, because the PL/I (F) compiler had a reputation as being a real dog, and one would not use something with that reputation to write an arguably "better" compiler. I used both compilers "back in the day", and there was no way one could shoehorn a compiler of such a massive language as PL/I into 44KB using a high level language.

However, it has been documented that the PL/I "Checkout" compiler WAS written using the PL/I "Optimizing Compiler", the arguably much improved compiler that came after the PL/I (F) level.

The following quote from an article from 1978 summaries the systems that PL/I was used to program:

PL/I, and a variant for systems programming, has been used successfully to program several large operating systems and compilers (notably MULTICS, OS/VS Release 2 Version 2, the PL/I Checkout compiler).

This is from The Early History and Characteristics of PL/I by George Radin, ACM SIGPLAN Notices, 13(8), 1978 RSzoc 18:34, 18 November 2006 (UTC)

  • The PL/I optimizing compiler required the PL/I runtime library to execute. Of course, this was rarely a restriction, but it was possible under VM to locate the two on different minidisks, which could mean access to one and not the other. Robert A.West (Talk) 08:26, 30 December 2006 (UTC)

[edit] PL/I AREAS

Can we insert something about notable/novel features in PL/I, in particular I am curious about AREAS.

NevilleDNZ 21:50, 23 May 2007 (UTC)

[edit] other drawbacks

As an ordinary programmer who has read up on PL/1 after learning C and Pascal, I would like to suggest 3 more reasons that the language is not more widely accepted. (1) The requirement that a subprogram could be embedded ANYWHERE inside a parent routine put another burden on the compiler writer, who would potentially have to save off data on the parent routine and then restore it when the subprogram finished. The feature itself was overkill; Pascal (and later ADA) confined subprograms to the declaration area with no loss of power.. (2) Although amazingly full of built-in data types, the language design completely missed out on the concept of the user-defined datatype, a very hot topic in the '70s. The only way that a programmer could declare two variables of the same complicated type was to use a clumsy "A LIKE B" mechanism, which would be a maintenance headache -- suppose B turned out to be obsolete during a later revision? (3) Wierd rules such as writing TRUE as '1'B, when both COBOL and FORTRAN already had much clearer syntax. CharlesTheBold 03:28, 30 July 2007 (UTC)

Well, as someone who wrote PL/I programs in the 1970s, I can tell you that none of these were problems at the time.
  1. While PL/I can certainly be accused of overkill, this wasn't an egregious example, and certainly wasn't the biggest imposition the language made on the compiler writers. If you want to find the part that made them go nuts, you only need to look as far as the macro language.
  2. The PL/I "structured data" type is exactly a "user-defined datatype", and it predated the C struct and Pascal record. This was a very common concept in the 1970s, and no serious language lacked it. PL/I even had C's *struct, using BASED(pointer), which was uncommon for a HLL of the time (of course, Assembler programmers used DSECTs for exactly that all the time). And nobody coded DECLARE A LIKE B; unless B was a structure and existed solely for that purpose.
  3. How hard is it to DECLARE TRUE BIT INIT('1'B); DECLARE FALSE BIT INIT('0'B);? And from a boolean perspective, C's "true is 1, false is anything else" concept is just wacky.
RossPatterson 00:57, 31 July 2007 (UTC)

Thank you for the historical perspective. I was of course evaluating the language from the point of view of 2007. I can tell the language was a powerful tool in the 1970's when compared to COBOL and FORTRAN. I understood about PL/1 structures, my point being that PL/1 seemed to operate by cloning a sample structure rather than instantiating a template -- this is a theoetical point which probably didn't make much practical difference in writing programs. CharlesTheBold 03:08, 10 August 2007 (UTC)

[edit] Typo in examples

Is the semi-colon missing from the PUT SKIP line of the second example intentional? --MarkMLl (talk) 13:49, 25 December 2007 (UTC)