[REBOL] Re: local vars in functions
From: holger:rebol at: 24-Apr-2002 14:53
On Tue, Apr 23, 2002 at 08:08:15PM -0700, Rishi Oswal wrote:
> One part of REBOL that can feel odd is when i have to
> define local variables of a function in the first
> block of the function. I find it a bit annoying to
> have to add new variables to the list for every little
> local variable I use. In addition, I feel it clutters
> up the first block and increases function size. In
> addition, the way it is currently done could make it
> easy to create hard to detect bugs.
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.
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.
> 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]
