[REBOL] Re: Embedded Object and Scope yet again...
From: larry::ecotope::com at: 11-May-2001 17:26
Hi Joel
> IMHO, using DO or USE is a more general mechanism, as it actually
> allows you to "embed" references wherever you wish, instead of being
> limited to the global level as with SET. For example:
>
I'm a little puzzled by your remark. SET is not limited to binding in the
global context. Rather, the target word is simply searched for up through
the context hierarchy. The first match determines the context where the
binding occurs, in exactly the same fashion as the look-up for the value of
a word. For example:
a: none
ob: context [
b: none
em-ob: context [
c: none
set 'a 52
set 'b 53
set 'c 54
]
]
After this code is run, we have:
>> a
== 52
>> ob/b
== 53
>> ob/em-ob/c
== 54
We could also have said
set [a b c] [52 53 54]
in the em-ob, with exactly the same results.
One limitation of SET is that it will only take a WORD or BLOCK as argument,
it will not accept a path. In that sense your DO construct is more general.
It is perhaps worth noting that in reading thousands of lines of "internal"
port, view, vid, and desktop code, I don't recall ever seeing USE used,
perhaps because it was broken (exported refs generated a GC crash)for most
of the last 2 years. Clearly, it is not really needed to create complex
REBOL programs.
-Larry
