On Tuesday, April 12, 2022 at 9:25:48 AM UTC+2, none albert wrote:

An indirect threaded Forth header contains the following elements:

[..]

SFA : Optional:identifies the source

[..]

The SFA is unlikely to be a constant, e.g. the source might be on
a network drive and the user accesses it from various accounts on
various operating systems, over a period of many years (i.e.
hardware revisions).

In iForth, we "install" the kernel sources, and the database of SFAs
for user source codes is dynamically adjusted/rebuild when loading.

-marcel

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An indirect threaded Forth header contains the following elements:
CFA : contains the address to jump to during EXECUTE
DFA : is a pointer to mutable data, in rare cases a constant
FFA : contains flags, properties of the word
LFA : identifies the wordlist, probably linking
NFA : Address of where the name of the word resides
SFA : Optional:identifies the source

These fields are constant. They need never be changed
once the word is created. It is amenable to be placed
in flash.

A VARIABLE and a BUFFER contains a pointer to
after the header or to an area in mutable RAM.
Though the content changes, the pointer needs not to.

Comes CREATE. The standard requires that there are two
mutable areas involved CREATE.
- DOES> identifies the action to be done by the CREATEd words
ISO require that it is possible to redefine indefinitely.
- The data field in the ISO sense. This is the run of the
mill data and is by nature mutable.
This is easily accommodated with a pointer to RAM that
contains two fields.

Implementors may choose this system to separate the immutable and the
mutable fields over baroque ad hoc headers where special cases
abound. Demanding that a CONSTANT is a CREATEd items,
is reminiscent of Java where even a simple integer is an object,
imposing overhead where it is no necessary.

[These insight came to me AD 2001. My impression is that
Ting, implementing a Forth in C++ comes to similar conclusions.]

P.S.
Code Data Link Flag Name Source
Note that this is in alphabetic order, as well of the
order of importance.
--
"in our communism country Viet Nam, people are forced to be
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none albert schrieb am Dienstag, 12. April 2022 um 09:25:48 UTC+2:

Implementors may choose this system to separate the immutable and the
mutable fields over baroque ad hoc headers where special cases
abound. Demanding that a CONSTANT is a CREATEd items,
is reminiscent of Java where even a simple integer is an object,
imposing overhead where it is no necessary.

Constants need not be CREATEd necessarily. However the Forth compiler
must know its value somehow. For this introspection CREATE is a cheap way.

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albert@cherry.(none) (albert) writes:

An indirect threaded Forth header contains the following elements:
CFA : contains the address to jump to during EXECUTE
DFA : is a pointer to mutable data, in rare cases a constant
FFA : contains flags, properties of the word
LFA : identifies the wordlist, probably linking
NFA : Address of where the name of the word resides
SFA : Optional:identifies the source

These fields are constant. They need never be changed
once the word is created.

The only thing specific to indirect threading is the code field (and
with code separated from headers you a code field is a good idea even
on a native-code system.

Flags are changed with IMMEDIATE, and on SMUDGE systems with SMUDGE.

On REVEAL systems the link field is changed on REVEAL.

Systems tend to use either SMUDGE or REVEAL (any exceptions?).

Comes CREATE. The standard requires that there are two
mutable areas involved CREATE.
- DOES> identifies the action to be done by the CREATEd words
ISO require that it is possible to redefine indefinitely.
- The data field in the ISO sense. This is the run of the
mill data and is by nature mutable.
This is easily accommodated with a pointer to RAM that
contains two fields.

Which means one indirection more for implementing dodoes.
Direct-to-flash systems have preferred to put the does-action address
into flash, foregoing standards compliance.

One thing to note is that IMMEDIATE, DOES>, and the unsmudging or
revealing of the current word all happen in Forth-2012 before the next
word is defined (locals and (non-2012) quotations muddle the picture a
little), so you can construct the current header in RAM, and create it
in flash when starting the next header. Issues: How to implement
RECURSE, ' and FIND (of the most recently defined word); anything
else?

Demanding that a CONSTANT is a CREATEd items,
is reminiscent of Java where even a simple integer is an object,
imposing overhead where it is no necessary.

Actually Java has so-called base types (e.g., int and long), which are
not objects. Many of the things you can do with objects you cannot do
with base types. Therefore Java also has a class Integer which boxes
int up as object (including object overhead), so you can use it where
an object is expected (e.g., with the collection classes).

- anton
--
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