Re: XPL Language (Heinz W. Wiggeshoff)
4 Aug 2000 21:41:30 -0400

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From: (Heinz W. Wiggeshoff)
Newsgroups: comp.compilers
Date: 4 Aug 2000 21:41:30 -0400
Organization: The National Capital FreeNet
References: 00-06-118 00-07-016 00-07-075 00-08-018
Keywords: architecture, history, comment

"Andy Johnson" ( writes:
> "Paul Dineen" <> wrote in message
>> Sander Vesik ( wrote:
>>: Peter Flass <> wrote:
>>: > A web site has been established for material related to the XPL
>>: > programming language at:
>>: >
>>: > XPL, developed in the 1970's was one of the earliest "compiler

    My copy of A Compiler Generator, W.M.McK.,J.J.H.,D.B.W. is c/r 1970.
    Quoting from the preface, "The XPL system was developed by the authors
    over a three year period ...", thus making it a child of the 1960's.

>>: > compilers", was widely ported, and was the basis for a number of other
>>: > languages such as the PL/M family.

    Ah yes: PL/M under CP/M running on a Z80. I'm sure I still have some
    listings of the Nabu Home Computer Metric Converter program from 1982/3.

>> And HAL/S, used on the space shuttle.
> ... and still in use, I might add. Of course, in true XPL tradition,
> the HAL/S compiler was written in XPL. It was also ported to several
> target computers, all used by various NASA labs for their projects
> (e.g. JPL used it for Galileo).
> Unfortunately, XPL had a lot of 360isms (e.g. string descriptors which
> used an 8 bit length and a 24 bit address in a 32 bit address word)

    Pardon me for being pedantic: the IBM System 360 architecture had a
    24 bit address space, (ie. 16 Mb), even though the 16 general registers
    were 32 bits wide. It wasn't til the System 370 series that addresses
    went to 31 bits. So storing [length,address] made sense in two ways:
    1) in those days, memory was hideously expensive;
    2) the length could be easily used for the EXecute of a MVC (MoVe
          Character), CLC (Compare Logical Character), TR (TRanslate),
          TRT (TRanslate and Test) instructions.

> which did not port very well to modern 32 bit architectures, so while

    Looking at the inside front cover of the book, the History of the XPL
    System diagram shows that it "ported" (eff, I hate that usage) to the
    B5500, using Algol no less!

> retargeting the HAL/S compiler was relatively straightforward,
> rehosting it was a nightmare.

    What jobs aren't?
[There was a version of XPL for the GE 635 done at Dartmouth, too. -John]

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