World: r4wp

so let's say you have something in a vid defintion

button "Test" [
	use [ f ][
		f: func [] []
	]
]

this is not subject to GC?

the local values are reset to none at each execution
 - that should have been:


the local variables are reset to NONE at every function call. After 
the function returns, the local variables are:
- in R2 they 
remember" the last (outermost call) value
- in R3 their values are inaccessible

this is not subject to GC?

 - Such a function looks like a subject to GC, but you need to find 
 out *when*.


- in R2 it is a subject to GC right after the button is pressed and 
released

- in R3 the function *may* persist after the button is pressed for 
the first time and *before* it is pressed for the second time

@Ladislav, have you written a paper on GC in Rebol ?

Aha, I was wrong with R2, actually in R2 the function persists between 
presses as well, but the reasons are different for R2 and R3

have you written a paper on GC in Rebol ?

 - the reason why the function persists between presses in R2 is based 
 on the fact that USE modifies its argument block "leaving" the local 
 variable in it. (it is described in Bindology). In R3 USE is a closure 
 written in REBOL, that is why there may be some "persistence" until 
 the USE function is called next time

IIRC in R3 closures do a BIND/copy of their bodies at every call, 
then execute the copy. As soon as the USE is finished executing its 
context and body are no longer referenced, at least if you didn't 
save a reference elsewhere. The context containing the 'f and the 
function it references would be able to be GC'd as soon as the USE 
returns.

The CLOSURE function in R2 should behave the same way, though it 
fakes it with mezz code.

Checked the USE implementation in R3 (source use) and you are right, 
Brian, so, the function in R3 shall not persist at all.

Yeah, R3's USE does a COPY/deep of the body, then make closure! uses 
the copy itself, then when executed (IIRC) the closure executes a 
BIND/copy of its body. So it copies its body more than once, but 
possibly less than twice.

Proof:
>> b: make closure! reduce [[] [append [] 1]]
>> b
== [1]
>> b
== [1]
>> mold :b
== "make closure! [[][append [] 1]]"

so to control GC one should in such a block unset the contents before 
leaving it ...

Sorry, didn't get that. In R2 if you are using functions not defined 
by the CLOSURE function then you might want to set some local variables 
to none before returning - that's what ALSO was for, btw. In R3 you 
don't need to unset anything because the GC will collect the set 
of values associated with the function's local variables after the 
function returns, or the whole context after a closure returns.

I guess you could use ALSO for R2's USE blocks too, or you could 
explicitly COPY/deep the body the way R3's USE does internally.

In R3 ... the GC will collect the set of values associated with the 
function's local variables
   


does it actually perform the GC, actively mark them as potentials, 
or simply unreference them?

It's a stack frame. Stack frames are automatically available for 
collection after the particular function call returns. All function 
words are referenced stack-relative.

They aren't collected immediately, they are collected when the collector 
runs.

Closures are different; the contexts that they create when they are 
called are basically the same as object contexts, with no stack-relative 
indirection needed, but the whole body and context are unreferenced 
after the call.

Whoah, it turns out that R3's closures do more than a regular BIND/copy 
when they run, they copy strings too. Surprised I hadn't tried that.
>> c: make closure! [[] [append "" 1]]
>> c
== "1"
>> mold :c
== {make closure! [[][append "" 1]]}

Same in R2: MAKE function! does more than a BIND/copy on its body 
as well, it also copies strings.
>> c: closure [] [append "" 1]
>> source c
c: func [][native action function! [[throw]] [append "" 1]]
>> c
== "1"
>> c
== "1"
>> source c
c: func [][native action function! [[throw]] [append "" 1]]

I always  though  BIND/copy    was   equivalent to    BIND COPY/deep

(which would copy strings AFAIK)

BIND/copy doesn't copy everything, it just copies everything that's 
bindable. So, no copying of strings, objects, functions, modules, 
lists or hashes, but it copies blocks, parens and paths. Words are 
of course copied because they're literal values.

At least that's what I was told. Let me check.

Functions and objects aren't copied, but everything else seems to 
be:


>> a: reduce ["" #{} 'a/b [] quote () make list! [] make hash! [] 
does [] context []]

== ["" #{} a/b [] () make list! [] make hash! [] func [][] make object! 
[
    ]]
>> b: bind/copy a 'a

== ["" #{} a/b [] () make list! [] make hash! [] func [][] make object! 
[
    ]]
>> map-each [x: y] b [same? :y first at a index? x]
== [false false false false false false false true true]

I guess that R2's make function! and R3's closures to a BIND/copy 
after all.

What we need is a document that discusses best practice for writing 
Rebol code.   Or is there such a beast?

Sure we have various idioms that people get used to using, but that's 
not the same thing

Ideally this should be in a book chapter .. perhaps Jerry could include 
it in his book as a guest chapter ?

map-each [x: y] [...] is an interesting use. I sometimes needed to 
get that "index" value but I didn't know that usage so I used forall 
instead. Good to learn.

Why this doesn't work?
e: func [] [f]

context [f: does [print "ok"] do bind 'e self] ;error: f has no value

or when I BIND the F inside E, still doesn't work:
o: context [f: does [print "ok"]]
bind first second :e o
e
** Script Error: f has no value

while this one works:
do bind first second :e o
== ok

doesn't F stay BINDed?

In your first try (bind 'e self), you're binding only this 'e word, 
not the :e function body, so if you replace it with: bind second 
:e self, it will work.


In second try, you're never binding 'e function body, you've just 
binded a new instance of 'f word that you have created using FIRST. 
That's why it works when you add DO, you're evaluating that new 'f 
instance which has the correct binding. Just remove FIRST, it will 
bind 'e body block and you'll get the result you've expected.

>> e: func [] [f]
>> o: context [f: does [print "ok"]]
>> bind second :e o
== [f]
>> e
ok

Got it, thanks a lot. I didn't know that FIRST gives me a "new" word, 
I thought that I'm BINDing *the* word itself and it should stay BINDed.

This confused me a bit:
>> o: context [a: 1 b: 2 c: 3]

>> foreach x bind [a b c] o [probe get x] ;this works, BINDs block 
to O

>> foreach x [a b c] [probe get bind x o] ;this works too, BINDs 
the word 'X to O

No, it doesn't bind 'x, it binds x, which is evaluated to 'a, 'b 
or 'c.

If you write in the loop: bind 'x o, it will fail, because 'x is 
not defined in o.

I see, thank you. And in the first line, it doesn't BIND *the block* 
to O, it BINDs the block of words (which are 'a, 'b and 'c) to O. 
It's clear now. Thanks!

Another interesting problem I have: I have a script as follow:
REBOL []
probe system/options/args
halt


I encap this script, no problem, it works as expected, console opens 
and "none" appears:
none
** Press enter to quit...

If I run it with some params like "test.exe --test"
["--test"]
** Press enter to quit... 


But if I run it with some parameters, like -c, --sec, it prints nothing? 
(-c and --sec seems to be special for rebol.exe but it works with 
-s which is special too)
** Press enter to quit...

Why and how PROBE doesn't produce an output?

Try with system/script/args instead.

Let me simplify:

REBOL []
print "ok"
print system/script/args
ask "test"


When I encap this script and run with a parameter like "-cxx" it 
doesn't print ANYTHING.

no "ok" no "test" nothing. BUT when I WRITE system/script/args to 
a file it looks it is there.

REBOL []
print "ok"

write %test.txt system/script/args ;there is "-cxx" in test.txt file.

yes I tried both "options" and "script", same result.

It's very weird, so we don't have a chance to use a parameter starting 
with -c (and many other) in our encapped executables.

More simplified, encap following script, run it with -c, -w or --sec, 
it prints nothing. Run it with -i, -t, -? it prints "ok".
REBOL [] print "ok" halt

Might be a bug where encapped REBOL tries to consume its own command-line 
options (while it shouldn't).

It looks like. I thought that it confusing with REBOL's own command-line 
parameters but it happens only for some of them not for all. So no 
chance to use *some* parameters.

Aha PRINT and PROBE doesn't work in encapped executable if command-line 
parameter includes a "c" character.

Any "c" character? I guess then that I was very lucky with Cheyenne: 
http://cheyenne-server.org/wiki/Main/Command
:-)

Definitely!! But we should keep that in mind.

-c means cgi ==> So not ouput to the console

Endo, when you are using set-words with MAP-EACH and R3's FOREACH, 
be sure to include at least one regular word, or it won't advance 
and you'll get an endless loop. We made that possible in order to 
support the foreach [x:] data [... take x ...] code pattern. It's 
the type of thing that would generate a warning in other languages, 
but REBOL is inherently incompatible with warnings.

BrianH: Yes I realized that at least one word is required.

sqlab: I encap a script and run the executable, so I should able 
to use any command line parameter. And I don't encap with cgi option. 
Also -w parameter has no such a problem (which is "no-window option 
for REBOL)

Anything that include "c" char prevents to print/probe to the console.

On the other hand it doesn't prevent opening console window. I see 
"** Press enter to quit" message when program HALTed but PRINTs don't 
output anything.