World: r3wp

The survey helped (even with those who didn't play the game ;)
Thans to all

thanks

I've written a patch to the assembler that implements a working OFFSET 
directive and label value fixups. I will submit it to RAMBO as an 
enhancement request.

I don't know enough about rebcode to do any voting - there any docs 
yet?

; You use it like this
label x
;...
offset y 5
sub y x
braw y

Note that label, offset and the branches all calculate relative to 
the end of their statements.

Just after the end, rather.

If anyone wants to test the patch, here it is.

REBOL []


use [fixup-rule label-rule label-fixup-rule label-error-rule here] 
[
    ; Initialize the intermediate rules
    label-rule: make block! 0
    label-fixup-rule: make block! 0
    label-error-rule: make block! 0
    ; Build the fixup-rule based on the opcode-rule
    fixup-rule: copy/deep rebcode*/opcode-rule
    parse fixup-rule [
        some [
            here: 
            lit-word! block! '| (

                unless find ['bra 'brat 'braf] here/1 [insert here/2 [label-error-rule 
                |]]
            ) |
            lit-word! 'word! '| (

                unless 'label = here/1 [here/2: [label-error-rule | word!]]
            ) |
            lit-word! | '| | 'block! | 'series! |
            'word! (here/1: [label-error-rule | word!]) |
            'any-type! (here/1: [label-fixup-rule | any-type!]) |
            into ['integer! '| 'word! | 'word! '| 'integer!] (
                insert here/1 [label-fixup-rule |]
            ) |
            block! (insert here/1 [label-error-rule |])
        ]
    ]
    ; Replace the fix-bl function

    rebcode*/fix-bl: func [block /local labels here there label rule] 
    bind [
        labels: make block! 16
        block-action: :fix-bl
        if debug? [print "=== Fixing binding and labels... ==="]
        parse block [
            some [
                here:
                subblock-rule (here/1: bind here/1 words)
                |

                'label word! (here/1: bind here/1 words insert insert tail labels 
                here/2 index? here)
                |
                'offset word! integer! (
                    here/1: bind 'set words
                    here/3: 3 + here/3 + index? here

                    if (here/3 < 1) or (here/3 > 1 + length? block) [
                        error/with here "Offset out of bounds:"
                    ]
                )
                |
                opcode-rule (here/1: bind here/1 words)
                |
                skip (error here)
            ]
        ]
        either 0 < length? labels [
            label-rule: make block! length? labels

            foreach [key val] labels [insert insert tail label-rule to-lit-word 
            key '|]
            clear back tail label-rule

            label-fixup-rule: [there: label-rule (there/1: 2 + select labels 
            there/1)]

            label-error-rule: [label-rule (error/with here "Cannot use label 
            here:")]
            rule: fixup-rule
        ] [
            rule: opcode-rule
        ]
        parse block [
            some [
                here:
                ['bra word! | 'brat word! | 'braf word!] (

                    if not label: select labels here/2 [error/with here "Missing label:"]
                    here/2: label - index? here
                )
                |
                rule
                |
                skip (error here)
            ]
        ]
    ] rebcode*
]

somebody must really like the add.i/add.d version. It's got priority 
20 now :)

can i have preincrement/postdecrement then?

if we go 68k. ;)

I don't like, it doesn't look like REBOL with the dot. Is it tuple 
or url? No, it isn't. So why the dot?

because its assembler and 68k did it that way. dont like it too.

have you voted already? :)

Yes, for the addi/addd version.

but it is not an assembly ;-) It is rebol dialect .... I agree with 
Kru ....

Have you voted? shall we vote again? :)

I agree with kru -- pity there is no option for making them look 
like refinements
  add/i
  add/d
  add   -- default is /i or /d or whatever is chosen

suggested that to. Was told its technially no option, they must be 
words.

or add-i/add-d. More REBOLish than dot.

exactly ....

I-am-already-used-to-rebolish-way :-)

The only advantages I can see to the dot (as opposed to the - ) is 
that it is less visually imposing and that it is easier for me to 
reach on my keyboard. These advantages are not insignificant, though.

Either dot or - would be OK to me.

here is a poll

Carl said: What I am thinking of for BRAW is this:

   BRAB [lab1 lab2 lab3] n


If N is out of range, the BRAB does not happen. That allows DEFAULT 
case without needing to compute it before teh BRAB.

Should BRAB be zero-based or 1-based?

(see checklists for the poll)

Are the labels statically replaced with offsets like they are with 
bra, done with runtime lookups of the label declaration, done with 
label offsets assigned to the words, or done some way that hasn't 
occured to me? Can numeric offsets be used, and if so are they absolute 
(within the block) or relative?

As for 0-based versus 1-based, let's compare:
0-based

- would allow branching on the basis of a modulus calculation, or 
other calculations that can result in zero

- would be more useful for implementing Duff's Device style switch 
statements, which I have found useful so far
1-based

- is more REBOL-like (if such a thing can be said of a goto statement)

- effectively has a 0-based branch with the default of continuing 
on (not as useful for Duff's Device stuff, as the 0 branch is usually 
the last in the code)

- is in keeping with the rest of the 0-based opcodes having the letter 
z on the end, while BRAB doesn't

I vote for 0-based, or both (BRAB/BRABZ).

If both is added as a choice to the poll, I'll change my vote from 
0-based.

Last question, can the block be passed in a word? Keep in mind that 
I am not requesting this, as there would be some negatives:

- You couldn't replace the labels statically with offsets in the 
assembler
- It would likely be slower and harder to JIT
- Copy/paste or compose can accomplish the same thing

Still, this deals with the most common usage scenario that I've found 
for computed branches so far, so I'm really pleased!

(by the "this" in my last statement, I meant the BRAB opcode, not 
indirect blocks)

By the way, if the block is required to be a literal, numeric offsets 
could be decided to be specified in either absolute or relative form. 
If you allow the block to specified through a word, absolute numeric 
offsets are the only practical option - this is probably another 
negative for label blocks in a word.

Common usage scenarios for BRAB would be C-style switch statements, 
state machines and token-threaded interpreters. Direct-threaded interpreters 
would still need BRAW, though are only practical when branching to 
an absolute offset so the current BRAW wouldn't work for them either.

If we have BRAB, can anyone think of a decent use for a BRAW to a 
relative offset? Every other usage of computed branches I can think 
of requires branches to absolute offsets to be at all practical. 
Have I missed something? Once we have BRAB, is there any reason to 
treat BRAW as a relative branch, besides simple implementation issues?

brab does accept a word for the first arg. offsets still need to 
be relative.

if the block is literal, the assembler takes care of replacing labels 
with offsets.

So you can specify numeric offsets, but they are only practical for 
a literally specified block. And you can still specify label words 
in an indirect block, so those are still useful too. Cool!

How about offset as argument? we can have 0, 1 or 65 then. Switching 
on letters. DO not know if that makes sense. :)

Volker, we already have that in the BRA opcode

I mean switch-ondex with offset.

brab -> brab .. 1, braz -> brab .. 0

Hmm, -1 0 1 code sometimes for lesser, equal, higher. brab .. -1

I think you still need the b in brabz to designate the block you 
are branching on.

Its about that little number at the end, not about my typos. ;)

Assuming you are going for both I mean.