World: r3wp

I know, i saw many implementations wich use recursive calls of parse 
(to deal with local var) in the past.
But i don't like that.

I saw it's slower most of the time than using recursive rules (well, 
it's the purpose of parse)

It's not always possible to refactor the parse rules to make the 
variable usage recursion-safe. Most of the time it is though.

even in that case, i prefer to code an emulated stack (using a block)

That can be slower than recursive calls to parse, depending, but 
at least you won't blow *that* stack.

There is another one advantage of using your own stack, you can break 
the process where you want and continue it later.
Used to do incremental parsing (even with recursives rules).

I also use block! stacks to avoid local words issues in recursive 
parse rules. It would be interesting to benchmark the two approaches 
: (recursive functions) vs (recursive parse rules+custom stack).

Here's an example: Come up with a recursive-parse-rule version of 
the ARRAY function, including the function value calls. Compare.

Wait, bad example. ARRAY is generative, so it is likely a bad candidate 
for PARSE.

afaik the rebol stack goes a few thousand funcs before failing... 
 but that depends on the amount of params you have on the functions, 
more args = more stack use.

rebol stack limit: 

>> i: 0 a: func [][i: i + 1 a] a
** Internal Error: Stack overflow
** Where: a
** Near: i: i + 1 a
>> i
== 14265

REBOL/Core 2.5.0.3.1
>>  i: 0 a: func [][i: i + 1 a] a
** Internal Error: Stack overflow
** Near: a
>> i
== 3151

Rebol/View 2.7.6, 64-bit Ubuntu Hardy
>>  i: 0 a: func [][i: i + 1 a] a                      
** Internal Error: Stack overflow
** Where: a
** Near: i: i + 1 a
>> i
== 1705

1704 on /Core 2.7.6 on the same system

wow this is pretty weird.

I tested  with rebview on windowsXP

REBOL/Core 2.7.6.4.2 on 32-bit Ubuntu 7.10
>> i
== 1705

REBOL/Core 2.7.5.2.4 on MacOSX Leopard:
>> i
== 1334

So WindowsXP is more recursion-friendly than Leopard...finally a 
good argument to not switch to MacOSX! ;-)

REBOL/Core 2.5.8.3.1
>> i
== 3150
REBOL/View 2.7.6.3.1
>> i
== 14265

Both on WinXP.

1334 parameterless functions... that's not nearly enough for many 
algorythms!  :-(  this really has to be addressed in R3.

its strange that view on XP has TEN times the amount of lowest target.

because of the compiler option /Strange in GCC i guess

but why did that get set differently on winxp... maybe its something 
that carl never really officially set as part of the distribution 
specifics.

Because Carl is not using GCC for Win builds?

Here's something stranger

>> i: 0 a: func [z][i: i + 1 a 1] a 1                    == 1704
>> i: 0 a: func [z y][i: i + 1 a 1 2] a 1 2            == 1706
>> i: 0 a: func [z y x][i: i + 1 a 1 2 3] a 1 2 3    == 1705

One stack for calls, one other for parameters perhaps

all is possible

possibly the stack includes a single payload block for calls... this 
would make sense, in preventing stack depth variance.

meaning parameters are not stored in the call stack :)

Carl would not be using GCC for Win builds, because REBOL is older 
than the short time period that GCC has been good on Windows

It would also depend on platform-specific stack handling.

possibly, yes, by indirection.  push stack [func args-block]

and args-block is a mem copy of the args block with local values

this is all speculation though... hehehe

what I am surprised overall is that rebol does not simply increase 
stack space.  isn't that possible in current OSes?

I mean, the interpreter, dynamically.

Function argument stacks are handled in function-specific value frame 
stacks in R2. They are stored in stack frames in R3, which changed 
the stack allocation to be more task-safe and have faster function 
calls.

Brian, i would be very suprised.

Rebol uses his own way to handle stacks, if not it would be unportable.

I think that last post from brian wasn't speculation... I think he 
actualy knows, being in the R3 internal loop  ;-)

i mean it's not platform specific.

This is one aspect of the internals that I actually am aware of, 
since it affects contexts. It's true: REBOL implements its own stacks, 
and doesn't use the C stack to call REBOL functions, just natives.

The platform-specific aspect could be affected by page and/or pointer 
alignment.

well, it an easy deduction, if not Rebol could not be portable

REBOL is not fully portable. The platform-specific parts are wrapped 
in APIs internally.

yes but the VM need to be fully portable

the core engine must be

This is why the R3 host code is separate, and will be open-sourced. 
The host code is non-portable. The VM can call API functions provided 
by the host code. This would be necessary for a variety of reasons, 
not the least of which is that memory management, tasking, networking, 
any number of things are implemented by different platforms differently.

http://www.openldap.org/lists/openldap-devel/200304/msg00123.html


Anyone made a REBOL version of this? It's a UTF-8 <-> ISO-8859-1 
converter in C.

hasn't peterwood just uploaded a pretty nice string en/decoder on 
rebol.org?

will check