[REBOL] Re: local vars in functions
From: lmecir:mbox:vol:cz at: 25-Apr-2002 10:17
Hi,
<Holger>
It is the result of REBOL being an interpreter, not a compiler. A compiler
examines the complete body of a function before generating code, so the
variable declaration can be anywhere. For an interpreter there are only two
options:
1. Make the context of a function "static", i.e. defined when a function is
declared. In that case declarations have to be explicit, i.e. during the
execution of "func" or "function", when the function is defined, all
variables
must be known. If declarations can appear in the body of a function then
there
is no way for "func" to know a list of all variables. Scanning the function
body is not an option, because declarations could be "hidden", e.g. with
something like [do rejoin ["a" ": " "1"]], i.e. there is no way for "func"
to
know about all declarations without actually executing the function.
</Holger>
Although that sounds logical, it is not the whole truth. Compare the way how
USE declares the local variables (the declarations don't appear in the BODY
argument) vs. the way how CONTEXT declares the local variables (the
declararions appear in the BLK argument). That surely isn't a non-option.
<Holger>
2. Make the context of a function "dynamic", i.e. make it empty when a
function
is declared, and extend it at run-time as needed. This is not how REBOL
currently works. Allowing this kind of model would require significant
changes
to the interpreter. It is the same problem as "extending" the context of
objects.
</Holger>
I am not a member of the "Object Extenders Club", nevertheless, the dynamic
function context surely *is* useful sometimes. Such functions (slower than
their native counterparts could be) we can create in Rebol even now.
<Holger>
> What I would like to see is another shortcut to
> creating local variables in any context (function,
> innerfunction, loop). The obvious way I see of doing
> this is as follows:
>
> myfunc: func [][
> localvar:: $25
Nooooo. Please do not do that :-).
You did not just create a notation with that, you actually created a new
datatype: a set-set-word!. We do not like to create new datatypes unless it
is
really necessary and the exact meaning, scope, usefulness etc. are very well
defined and can be clearly demonstrated. Creating a new datatype only to
shortcut variable declaration seems ... inappropriate, for lack of a better
word :-).
--
Holger Kruse
[kruse--nordicglobal--com]
--
</Holger>
I think, that it can really be useful, although the proposal made by Rishi
is not a complete thing.
