Wade Bowmer <[EMAIL PROTECTED]> wrote:
" Secondly, I had an idea of how to add references to Unicon in a
" limited but still useful capacity.
Neat!
"
" What I had in mind was a built-in function, probably called
" ref(), that was the reverse of copy(). That is, instead of making
" sure you had a value, it tried to make what you gave it a
" reference. So that
"
" a := ref(b)
"
" ... would result in two names for the same variable, and of
" course:
"
" x := ref(z + 15)
"
" ... should be absolutely identical to:
"
" x := z + 15
Is this to be similar to c++ references, Fortran pointer/target, or
Ada access types?
I haven't given it any deep thought, but some things to think about
may be:
1. Are you sure that 'ref' should revert to ':=' when given an
expression rather than a variable? Two other options come
to mind:
a) fail if i) the 'ref' parameter isn't a variable name or
ii) the expression doesn't return a LHS (e.g.:
L[1] for a list L)
b) create a reference to the value.
2. What would/should be the result of 'x := ref(f())' where procedure
'f' is:
a) procedure f()
static w := <whatever>
return w
end
(Here, 'f() := <something>' changes the value of static var 'w'.
Since 'w' is permanent, it's not unreasonable to have a
reference to it.)
b) procedure f()
local L := [1, 2, 3]
return L[1]
end
(Here, 'f() := 23' doesn't cause an error, but has no observable
effect. Since 'L' disappears when the call completes, it doesn't
make sense to have a reference to it unless the call leaves 'L'
for the GC. What happens to 'L[2]' and 'L[3]'?)
3. What happens if the referenced variable goes out of scope? E.g.:
a) procedure f(x)
local y := 1
x := y
.
:
end
called as 'a := f(ref(i))'
b) procedure f(x)
local y := 1
x := ref(y) #<***
.
:
end
called as 'a := f(ref(i))'
What happens if 'y' is a structure?
4. Does the GC have to keep track of references?
5. Do we have to distinguish between 'ref' assignment and ':=', e.g.:
b := 4
a := ref(b) # 'a' is implicitly a pointer?
a := 5 # b = 5
a := ref(c) # what happens to the reference to 'b'?
# does 'b' now refer to 'c'?
"
" The biggest use for this would be to pass variables by reference
" into functions. You can sort of do it now, by doing:
"
" p := [ x ] f(p)
"
" ... but you can't go back to using x after you make that call;
" you have to use p[1]. It would be so much easier if you could do
"
" f(ref(x))
"
" ... then x would still be valid and the function f() could modify
" it, too.
"
That would be handy and is something I have wanted to do. I wonder
if this may not also allow something like:
ce1 := create x | y | z
ce2 := !f(a, x) # f returns a list longer than 2
while @ce1 := @ce2
and have x, y, and z assigned.
"
" Note, I've not spent more than about 30 minutes in the Unicon
Well, that's about 30 minutes longer than I have :^)
" code. And it's late at night. And I'm sure there will be some
" possibly lively discussion about this. Thoughts? Clues?
"
" Wade.
"
Thanks in advance for the effort!
Michael Borek
"Death before Dishonour; Beer before Lunch"
__________________________________________________________________
New! Unlimited Netscape Internet Service.
Only $9.95 a month -- Sign up today at http://isp.netscape.com/register
Act now to get a personalized email address!
Netscape. Just the Net You Need.
-------------------------------------------------------
SF.Net is sponsored by: Speed Start Your Linux Apps Now.
Build and deploy apps & Web services for Linux with
a free DVD software kit from IBM. Click Now!
http://ads.osdn.com/?ad_id=1356&alloc_id=3438&op=click
_______________________________________________
Unicon-group mailing list
[EMAIL PROTECTED]
https://lists.sourceforge.net/lists/listinfo/unicon-group
