World: r3wp

the consequence of such complicated rules

 - I don't understand where the complication is. Should writing a: 
 [...] also do a copy? Should everything do a copy? You're arguing 
 that sometimes REBOL should copy things, sometimes not. *That* is 
 a list of complicated rules.

most programmers will put in COPY/DEEP many places in the code in 
front of blocks.
 - how many programs on rebol.org do this?

BIND modifying the block is a useful feature at times. For example, 
the copy that has been added "for security reasons" in many places 
makes a number of "tricks" harder to do.

To me, REBOL does have scope, it's just different from most languages.

 - oh well, of course you are free to change the definition of  the 
 word "scope" so that it fits REBOL... lol.

MOLD missing words context: where did I ever say this was a feature? 
As Ladislav said, this is just a non-trivial problem, because to 
solve it you may have to save the whole interpreter state. (One of 
your X there is bound to system/words, if you save that you basically 
save everything.)

So the block should define the binding, not each word.
 - that kills dialecting.


Geomol, really, have a look at Scheme. It works exactly like you 
want... REBOL works differently for a reason.

Ladislav, if you try follow my thoughts, you can figure that out 
yourself.


Steeve, maybe that law is a design flaw, that causes many problems? 
Like the example returning "bug", which started much of this conversation.


Gabriele, ... Gabriele, you strengten my tolerance, and thank you 
for that. "that kills dialecting" I've seen you writing that before, 
and it puzzles me every time. (Well, probably different understanding 
again.) Thank you for suggesting Scheme, but I don't have time to 
dig into a new language right now.

Should we let it rest?

Ladislav, if you try follow my thoughts, you can figure that out 
yourself.
 I cannot, but nevermind

Gabriele, it hard to have a conversation, when you go to extremes 
like in the following:


I don't understand where the complication is. Should writing a: [...] 
also do a copy? Should everything do a copy? You're arguing that 
sometimes REBOL should copy things, sometimes not. *That* is a list 
of complicated rules.


Do REBOL copy things sometimes today? Like in function definitions:

make function! spec body


Maybe REBOL should copy in the example, we discuss, maybe it's a 
bad idea. The complication (for me and most likely others) in the 
above example is, when I read it, I would expect some output from 
my intuition. The actual output is different, and it's really hard 
to see, why that output is intentional.

MAKE function! doesn't copy its arguments. The wrappers for it in 
R3 copy their arguments explicitly, but the MAKE operation doesn't, 
for efficiency and flexibility. The same goes for MAKE closure! vs. 
CLOSURE, and MAKE module! vs. MODULE (for unbinding, not copying).

None of these copy by default for three reasons:

- You can't uncopy something that's been copied, but you can copy 
something that hasn't been copied yet.

- MAKE doesn't take options that can't fit in its argument(s), so 
optional behavior can only happen if the spec says so.

- Efficiency means avoiding copying, particularly in a non-compiled 
language. That's why a so many functions are modifying.

Yes, and there is no reason, why such a rule could not be held for 
e.g. CONTEXT, to follow the suit as well

Yup. The reason that CONTEXT currently doesn't copy is the same as 
why MODULE doesn't copy: They are generally used for one-off creations, 
based on large specs that are rarely reused, and inefficient to deep-copy. 
We could easily make them copy, but it would continue to be a bad 
idea for those reasons.

The FUNC used to load the mezzanine functions at startup doesn't 
copy either, for the same efficiency reasons.

Hmm, I doubt it is needed

Doing it that way shrinks the startup time and memory quite a bit. 
There's a lot of the loading process that is dedicated to reducing 
code copying.

This is also why that while most of the large mezzanine functions 
are written using FUNCT, the actual mezzanine build process converts 
those definitions to calls to the non-copying FUNC, with no preprocessing 
or copying needed at startup time. The user-level mezzanine FUNC 
is copying for safety reasons though.

We all know you can make REBOL do just about anything. We also know 
there are a few things that trip people up (e.g. copying series values 
defined in funcs). My questions for John are: 


1) Has this behavior ever been behind a bug in any of your REBOL 
code? If so, what was the context and what was the impact (e.g., 
how did you work around it)?


2) If you got your wish, what would the consequences be? i.e., how 
would it change REBOL?

More confusion?

>> body: [a + b]
== [a + b]
>> f: make function! [a b] body
>> pick :f 2
== [a + b]
>> same? body pick :f 2
== false
>> insert body '-
== [a + b]
>> body
== [- a + b]
>> pick :f 2
== [a + b]
>> f 1 2
== 3


To me, MAKE function! seem to copy the body block. What are the arguments, 
that the body block isn't copied?

Gregg, I get back to you, as answering your questions might take 
this into another direction.

Geomol, it's not make that copies the function body, it is pick. 
that was added for "security" reasons. blame Brian for this sort 
of things. :P

Gabriele, that can't be true. See:

>> b: [a]
== [a]
>> blk: []
== []
>> insert/only blk b
== []
>> blk
== [[a]]
>> same? b pick blk 1
== true

(Notice this is the "Core" group, not the "!REBOL3" group, and I'm 
talking R2.)

Gregg: "1) Has this behavior ever been behind a bug in any of your 
REBOL code? If so, what was the context and what was the impact (e.g., 
how did you work around it)?" - you should not have asked this question, 
since the answer is already present above

Geomol, I meant PICK when done on a function! value.

ok, no, you're right and that was R3. R2 copies on make function!. 
to me, *this* is a bug. or rather, either make should always copy 
or it should never do it. having exceptions is silly.

(note, exceptions are added to make people happy wrt to "bugs" like 
the one you described above. the result is more confusion imho.)

(always copy would make sense only if rebol could do copy on write 
- which is a bit tricky. given the way rebol works "never copy" makes 
much more sense, then you add copy to helpers like FUNC etc. Then, 
we can discuss whether CONTEXT should have a copy, and imho it should 
not because this "bug" never happens in practice.)

'this "bug" never happens in practice' - that is actually false

Moreover, it is silly, that all helpers copy, but CONTEXT does not, 
isn't it?

;-)

Ok, now we're getting somewhere. A question is raised, if MAKE should 
copy arguments given to it. This isn't the bug, as I see it, and 
I'll explain that a bit later.


But first, if MAKE disn't copy the body block when making a function, 
then we would be able to change the function by changing the original 
block. Like:

>> b: []   
== []
>> f: make function! [] b
>> f
>> insert b 42
== []
>> f


After the last call to f, we would get the result 42, if the body 
block wasn't copied. This is not desirable to me. Is it to you guys?

Then the MAKE object! . The block given to make this time is also 
copied, as this shows:

>> b: [a: 1]
== [a: 1]
>> o: make object! b
>> third :o     
== [a: 1]
>> same? b third :o
== false
>> append b [c: 2]
== [a: 1 c: 2]
>> third :o
== [a: 1]


So the block is copied, and then that's not the reason, the example 
from Ladislav's Bindology returns "bug".

Let's look at the example again. My version of the example is this:

f: func [x] [
    get in make object! [
        a: "ok"
        if x = 1 [
            a: "bug!"
            f 2
            a: "ok"
        ]
    ] 'a
]

I can pick the inner-most block this way:

>> b1: pick pick pick :f 2 5 7
== [
    a: "bug!" 
    f 2 
    a: "ok"
]

Now I run the example and pick the block again:

>> b2: pick pick pick :f 2 5 7
== [
    a: "bug!" 
    f 2 
    a: "ok"
]
>> same? b1 b2
== true

It's the same block.

I ran the example before b2 was picked with:

>> f 1
== "bug!"


So, running the example, which makes the object doesn't change the 
block (other than binding) and MAKE object! makes a copy of the block. 
The conclution to me is, that MAKE rebinds the block before copying 
it, where it should do that after making its copy, andt that is a 
bug.

Sorry for a couple of long posts, but this takes room to explain.

Also, if MAKE object! didn't copy the block argument, then the code 
in the block would still be in the object, and this is not desirable. 
That is, the object would hold all this information:

[
    a: "ok" 
    if x = 1 [
        a: "bug!" 
        f 2 
        a: "ok"
    ]
]

Instead of just [a: 1].

Sorry, instead of just [a: "ok"].

MAKE object! makes a copy of the block

 I gave a proof it does not make a copy. Interesting, how much you 
 try to reinvent the wheel, taking into account, that the correct 
 explanation to your results is available from public sources.

A copy of the MAKE OBJECT! block is actually never made, as this 
example shows:

b: [a: 1 "this is the block"]
o: make object! b
third o


good luck with reinventing the wheel instead of reading publicly 
availalbe sources that explain what is going on

The fact is, that the object does not "store" any block, only the 
THIRD function tries to "create" something like that

That can be easily proven by examining:

same? third o third o

Cool, thanks! This is complicated! :)

So we're back to, it isn't a bug, that MAKE doesn't copy the block, 
when making objects. It's intended behaviour. And MAKE does copy 
the block, when making functions, and that is intended behaviour 
too. And the SECOND function doesn't try to create a block, when 
used on functions:

>> f: does []
>> same? second :f second :f
== true

while THIRD does do that, when used on objects.

Gregg, about your questions.


1) Has this behavior ever been behind a bug in any of your REBOL 
code? If so, what was the context and what was the impact (e.g., 
how did you work around it)?


I guess, you mean series inside functions. I'm not for everything 
should do a copy, as Gabriele imply. The problem with series in functions 
is only a problem, because functions in REBOL isn't functions in 
the traditional understanding. They are semi-closures. If they were 
functions, the local values would just be on the stack. Because the 
locals live on, this was a problem for me years ago. First I solved 
it by putting COPY in series definitions, then I in many cases changed 
to just do a CLEAR, like in:

local-block: clear []


Now with the discovered behaviour regarding objects, I find the binding 
rules so complicated, that I would forget, how it works in two weeks. 
I will remember, that I have to be very careful, when making objects 
inside functions, especially if it's recursive functions. The consequence 
for me is, that I will probably put COPY/DEEP in, when making objects. 
As I won't start new big projects in REBOL, I will probably not do 
this a lot in practice.

The second question was:


2) If you got your wish, what would the consequences be? i.e., how 
would it change REBOL?


When making an object in REBOL, I think of it as making a context. 
When making a function, I also assiciate this with making a context. 
If the rules were somehow similar regarding the two different contexts, 
it would be easier or more "simple", as I see it.


If your question was about binding, that I suggest blocks should 
define the binding and not each word, then that's a change, I find 
interesting but can't see the full consequences of. I think, it would 
work, and work well.

And MAKE does copy the block, when making functions, and that is 
intended behaviour too.
 - not exactly, in R3 it does not

 And the SECOND function doesn't try to create a block, when used 
 on functions:
 - again, not exactly, in R3 this has changed

On the other hand, it is not hard to understand why the THIRD function 
creates the block: there is no other option, since the block is not 
available from anywhere, so it *has to* create it

...Because the locals live on, this was a problem for me years ago. 
First I solved it by putting COPY in series definitions...

 - sorry to chime in, but I simply have to. The issues you mention 
 (series in functions, extent of function locals) are not related. 
 For example, the extent of function locals has changed a bit in R3, 
 while the issue with series remains unchanged.