Re: Word name storage quirk in VAX fig-Forth

David Meyer <papa@sdf.org> 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
--
M. Anton Ertl  http://www.complang.tuwien.ac.at/anton/home.html
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