[SLOF] [PATCH] slof/engine.in: remove the "COMPILE" keyword

[Kautuk Consul]

Hi Segher,

On 2024-01-31 10:11:05, Segher Boessenkool wrote:
> On Tue, Jan 23, 2024 at 04:11:09PM +0530, Kautuk Consul wrote:
> > So, 2 questions for Segher:
> > i)	Can we use the standard DOTICK DOCOL COMPILE, and DOTICK SEMICOLON
> > COMPILE, method for +COMP and -COMP respectively ? That seems to be more
> > efficient as that doesn't use the return stack.
> 
> No, the standard requires the word COMPILE to exist.  It is a standard
> Forth word, historical (it isn't part of ANS Forth).

Yes, I do understand that now.
But I am just proposing that we use "DOTICK DOCOL COMPILE," instead of
"COMPILE DOCOL" in "+COMP" so that the compiler doesn't have
to use the return stack as it is not required in "+COMP". Same thing goes for -COMP.
It's a minor performance improvement, but I spotted this while reviewing
the code so I decided to send this patch.
> 
> In compiled code of course you will see what is compiled by the
> compiler, not the source code.  COMPILE is compilation-only word, so you
> do not see it in command scripts even.  In very old Forth
> implementations it would be simply compiled like anything, so
> "COMPILE DUP" would end up as two cells with the addresses of "COMPILE"
> and "DUP" in the generated (indirect-threaded or direct-threaded) code,
> and at runtime the COMPILE would get the next cell and plop it into the
> currently compiling definition.  But not anymore: this cannot work for
> more modern implementations, better optimising implementations; we now
> have POSTPONE instead of COMPILE (and [COMPILE] , in ye olde days the
> programmer had to know which words were immediate words).
> 
> engine.in is compiled code (well almost, not yet fixed to any absolute
> address and stuff).
> 
> > ii)	Instead of EXIT used in -COMP can we use SEMICOLON instead to
> > compile into HERE ? That seems to be in line with how the col() macro
> > is defined and gives better information to the reader of this code that
> > the compiler is trying to generate the same "DOCOL <forth words> SEMICOLON"
> > format of defining subroutines.
> 
> I have no idea what you mean, sorry.  Propose a patch, and say why that
> would be better?
What I mean is that the col() macro is defined by:
#define col(_xt, _def...) def(DOCOL _def SEMICOLON)

+COMP and -COMP are defined by:
col(+COMP STATE @ 1 STATE +! 0BRANCH(1) EXIT HERE THERE ! COMP-BUFFER DOTO HERE DOTICK DOCOL COMPILE,)
col(-COMP -1 STATE +! STATE @ 0BRANCH(1) EXIT DOTICK SEMICOLON COMPILE, THERE @ DOTO HERE COMP-BUFFER EXECUTE)

The above 2 lines compile the same "DOCOL _def SEMICOLON" type of
subroutines for IF, WHILE, CASE, ENDCASE, BEGIN, UNTIL, etc. when they
are not defined in any coloon definition of a FORTH subroutine.

But, the way +COMP and -COMP are currently working is that they are
compiling the following code into HERE:
DOCOL _def EXIT

Instead of compiling the EXIT Forth routine in -COMP I will try to make
the compiler compile the following format for IF, WHILE, CASE, ENDCASE,
BEGIN, UNTIL, etc. :
DOCOL _def SEMICOLON

I can propose a patch for both the "COMPILE," as well as this SEMICOLON
idea together once you are okay with my suggestions.

Thanks!

> 
> 
> Segher