World: r3wp

Geomol wrote:

mult2: func ['value] [...]


as I said many times I am wholeheartedly against this nontransparent 
argument passing variant. I consider

mult2: func [value] [...]

always better than that

Geomol: again, what you ask for needs at least a couple new datatypes, 
and breaks the evaluation semantics... you may see it as "simpler" 
but i see it as a huge complication of the language (a useless one, 
too)

Hm, maybe I didn't explain myself well enough. All this come from 
Carl's blog about ++/--. He writes

count: 0
++ count ; add one


I see ++ as a function with calling-by-reference. ++ isn't called 
with the value of count but with it's reference, so ++ can change 
the value of count. My point is, that if ++ is introduced in the 
language, it may be a good idea to implement a method, so programmers 
easily can make their own ++ kind of functions.

That's all.

And the other way around, if it isn't easily possible to introduce 
such a method (calling by reference), then it may not be a good idea 
to introduce ++/--.

the lit-argument passing method is already present in the language 
(although I am against it, to express my preferences, since ++ 'count 
looks good enough to me being referentially transparent - try to 
write ++ pick [a b] 1 using the nontransparent argument passing method), 
so you are indeed requesting much more than that complicating the 
languge without offering an advantage that would justify it

You can also not write your own 'do. IMO itis ok that  some things 
 are only possible at native level. Its  not  lisp.

inc/dec/shift are essential enough for speed and commodity, these 
could be an exception. (Maybe  evenn '<< and '>> as  operators, and 
allowed  in parser?)

as opposed to that, I guess that these cannot save much time anyway

four interpreter-steps instead of one? in a tight  search-loop?  
 until[pair? ++ blk]

btw i prefer post-increment.

but thats a rebcode-case anyway.

i dont like  the repitition when incrementing, moving. the two 'count. 
But  i have no good syntax :(

Geomol: as ladislav said, that method is already there. rebol does 
not have "by reference", so if you want passing "by reference" you're 
going to change the language a lot.

Yes, I see.

I understand, why Carl is concerned, if he should include ++/-- or 
not. I don't think, we have something similar today working on scalar 
data types. An action like NEGATE doesn't change the variable holding 
the scalar data type:

>> negate 4
== -4
>> a: 4
>> negate a
== -4
>> a
== 4

So I bet it'll be confusing, if ++/-- does change the variable.

What would this be called, then?  (I remember it came up before - 
I mean, what's this kind of variable passing called, if not "by reference" 
?)

>> ++: func ['X][set X (1 + get X)]
>> foo: 5
== 5
>> ++ foo
== 6
>> foo
== 6

another variant demonstrating the advantages of "transparent" argument 
passing:

++: func [x] [set x 1 + get x]
foo: 5
++ 'foo ; == 6
foo ; == 6
++ pick [foo bar] 1 ; == 7
foo ; == 7

Izkata: you cannot call it "by reference", since you are actually 
passing the value you are manipulating - the word, not a reference 
to it

ladislav, that in C is just what a reference is... you pass not the 
value, but the pointer which refers to it... in REBOL that is a word. 
 under the hood, in REBOL everything really is a pointer to a value, 
with an offset within a context, no?

ladislav, that in C is just what a reference is

 - that looks like an error to me - references are in C++ actually. 
 Pointers are passed "by value" in C

in REBOL everything really is a pointer to a value, with an offset 
within a context, no?

 - you can explore how REBOL values look using my hints in this world 
 and at REP

lad: a reference to a number is a common usage term which means get 
the pointer to the memory area where the number is contained... not 
the value at that pointer.  in C series variables have to be pointers, 
but numbers aren't usually pointers.  thus the reference to that 
number is its pointer.

if you pass the reference, and chance the value at that adress and 
change it in place... all "references" to it will change.

so I think you are both talking the same language, but with different 
terminology.... based on your usage of C..  :-)

(or C++)

what you are saying is terminologically misleading. "Pass by value" 
has got a broadly accepted meaning as well as "pass by reference". 
If you pass a pointer in C, then you pass it "by value" according 
to the definition.

hehe, but you are passing the "value by reference"  ;-)

hehe isn't programming fun?  :-D

Isn't the real difference between passing a pointer by value or by 
reference is that when you are explicitly passing a pointer it is 
by value and when you are implicitly passing a pointer then it is 
by reference.

(Well that is my understanding from the difference in Pascal).

that is correct

but what about values which are not defined as pointers like an int.

so what, are you trying to convince me, that in REBOL ints are "passed 
by reference"?

(if you speak about the C/C++ family then it is easy - in C++ you 
can pass int by reference, in C you cannot)

REBOL passes values unless the function requires a "pointer" to them. 
 (not really a pointer, but in use pretty much the same result).

so I guess in your terminology, only series can be "references" in 
rebol right?

Surely one of the distinctions of pass by value and pass by reference 
is that in pass by value you work on a copy of the value not the 
value originally refered to:

>> a: 1                          
== 1
>> b: func [a [integer!]][ a: 2]
>> print b a                     
2
>> a: 1                         
== 1

yes.

series can be references
 - actually not

so in your terms, how could a reference be "simulated" in rebol?

or can they?

why not?, but it does not influence the fact, that when you are passing 
a word to a function, then you are "passing it by value", not by 
reference, I can easily show you a proof

(almost the same Peter wrote above)

I think I just see the nuance in our statements... you're talking 
about the word supplied to the function I'm really talking about 
its value.  so yess I agree.

except my example was wrong

I'm with Ladislav on the C front, but it can be said that words are 
associated with their values, so they are pointers to them.

yes, that is OK

you never get the actual word submitted to the function, even in 
the lit-word arg passing, you still get a new word within the function. 
 but its pointing to the same value.

ah.. what a little scribble on a piece of paper would do in these 
instances  ;-)

...that is the "pass by value" business

one exception regarding "pointer business" in REBOL: only words bound 
to a context can "point" to values

yes... the act of binding creates the association (to use Anton's 
term :-)