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  • Word name storage quirk in VAX fig-Forth

    From David Meyer@21:1/5 to All on Wed Apr 16 22:35:29 2025
    I've been dusting-off fig-Forth for VAX-11 and noticed that every word
    in the dictionary has 128 added to the character code of the last
    character in the word name. Everything seems to work except a few things
    like VLIST (prints a list of defined words like WORDS in ANS Forth)
    printing a garbage character at the end of each word.

    I wrote my own version of VLIST to unmunge the last characters, but it's
    hard to believe it's been messed up for 40 years. Is there some
    peculiarity in fig-Forth or the VAX-11 (I'm using significantly later
    hardware and OS) that made this work correctly back in the day?

    --
    David Meyer
    Takarazuka, Japan
    [email protected]

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  • From David Schultz@21:1/5 to David Meyer on Wed Apr 16 09:53:47 2025
    On 4/16/25 8:35 AM, David Meyer wrote:
    I've been dusting-off fig-Forth for VAX-11 and noticed that every word
    in the dictionary has 128 added to the character code of the last
    character in the word name. Everything seems to work except a few things
    like VLIST (prints a list of defined words like WORDS in ANS Forth)
    printing a garbage character at the end of each word.

    I wrote my own version of VLIST to unmunge the last characters, but it's
    hard to believe it's been messed up for 40 years. Is there some
    peculiarity in fig-Forth or the VAX-11 (I'm using significantly later hardware and OS) that made this work correctly back in the day?


    Checking a handy fig-Forth implementation, I see that EMIT clears that
    bit...

    --
    http://davesrocketworks.com
    David Schultz
    "The cheeper the crook, the gaudier the patter." - Sam Spade

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  • From Anton Ertl@21:1/5 to David Meyer on Wed Apr 16 16:18:56 2025
    David Meyer <[email protected]> writes:
    I've been dusting-off fig-Forth for VAX-11 and noticed that every word
    in the dictionary has 128 added to the character code of the last
    character in the word name.
    ...
    Is there some
    peculiarity in fig-Forth or the VAX-11 (I'm using significantly later >hardware and OS) that made this work correctly back in the day?

    David Schultz gave the answer to why VLIST works in fig-Forth.

    Here's the reason why the last bit is set: Fig-Forth has "variable
    length names" as headline feature, whereas earlier Forth systems only
    stored the length and 3 characters (i.e., VLIST would output its own
    name as VLI__ or so), and would match/conflict with, e.g., VLIKE.

    But unlike modern systems, fig-Forth does not always store the full
    length of the name. Instead, you could set the length of the number
    of characters to be stored by setting a variable. That variable can
    change from one definition to the next, so you do not know from this
    variable how many characters are stored for a particular name.
    Instead, you know the last stored character by looking whether the
    most significant bit is set (the most significant bit of the
    count+flags byte is also set to allow finding it from the other end.

    - anton
    --
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    comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
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  • From David Schultz@21:1/5 to Anton Ertl on Wed Apr 16 12:20:02 2025
    On 4/16/25 11:18 AM, Anton Ertl wrote:
    Here's the reason why the last bit is set: Fig-Forth has "variable
    length names" as headline feature, whereas earlier Forth systems only
    stored the length and 3 characters (i.e., VLIST would output its own
    name as VLI__ or so), and would match/conflict with, e.g., VLIKE.

    Way back when I bought copies of the fig listings, I also bought a copy
    of the Glossary, Model, and Editor document. Which had little details
    like this.

    Plus of course the 6502 model implementation (in Forth) including an
    EMIT that has "7F # AND,"

    Later you could get things like the Systems Guide to fig-Forth.

    All available online these days of course. For free. Sigh.

    --
    http://davesrocketworks.com
    David Schultz
    "The cheeper the crook, the gaudier the patter." - Sam Spade

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  • From David Meyer@21:1/5 to All on Thu Apr 17 08:31:30 2025
    It occurred to me that another factor in this is that the VAX-11 OS used
    7-bit ASCII as its character set, so perhaps terminals and printers of
    that time would just print the character indicated by the lower 7 bits
    of each byte they were sent, ignoring the high bit. So I am seeing
    munged characters because I'm using equipment that looks at all 8 bits
    for character codes?
    --
    David Meyer
    Takarazuka, Japan
    [email protected]

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  • From David Meyer@21:1/5 to dxf on Thu Apr 17 13:22:19 2025
    dxf <[email protected]> writes:

    Ideally FigForth should allow 8-bit EMITs and ID. rewritten to use a
    127 AND EMIT loop instead of TYPE .

    That works. VLIST using the new ID. prints the list of words unmunged as expected.

    --
    David Meyer
    Takarazuka, Japan
    [email protected]

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  • From [email protected]@21:1/5 to Anton Ertl on Thu Apr 17 14:30:43 2025
    In article <[email protected]>,
    Anton Ertl <[email protected]> wrote:
    David Meyer <[email protected]> writes:
    I've been dusting-off fig-Forth for VAX-11 and noticed that every word
    in the dictionary has 128 added to the character code of the last
    character in the word name.
    ...
    Is there some
    peculiarity in fig-Forth or the VAX-11 (I'm using significantly later >>hardware and OS) that made this work correctly back in the day?

    David Schultz gave the answer to why VLIST works in fig-Forth.

    Here's the reason why the last bit is set: Fig-Forth has "variable
    length names" as headline feature, whereas earlier Forth systems only
    stored the length and 3 characters (i.e., VLIST would output its own
    name as VLI__ or so), and would match/conflict with, e.g., VLIKE.

    But unlike modern systems, fig-Forth does not always store the full
    length of the name. Instead, you could set the length of the number
    of characters to be stored by setting a variable. That variable can
    change from one definition to the next, so you do not know from this
    variable how many characters are stored for a particular name.
    Instead, you know the last stored character by looking whether the
    most significant bit is set (the most significant bit of the
    count+flags byte is also set to allow finding it from the other end.

    This allowed to define $.... as a word, storing the length (5) and
    only one letter of the name.
    So any word like $1AC4 matches, and $ could try to find out what
    number was meant. $QQQQ gives an error. So you could have a
    hex number without changing BASE.

    This is similar to PREFIX in ciforth:
    : $ (NUMBER) .... ; PREFIX IMMEDIATE
    The difference is that the name of $ matches any word that commences
    with $ , e.g. $1AC4 and $QQQQRRRR , governed by a bit in the flag field
    of $.
    The prefix has the responsability to advance the parse pointer (aka >IN)
    unlike in fig-Forth. The parse pointer was left immediately behind $.
    PREFIXes can handle arbitrary length and strings containing blank space.


    - anton
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