OpenEuphoria

Re: Uninitialized Variables

• Posted by Derek Parnell <ddparnell at bigpond.com> Mar 23, 2002
• 441 views

----- Original Message -----
From: "Chris Bensler" <bensler at mail.com>
To: "EUforum" <EUforum at topica.com>
Subject: RE: Uninitialized Variables


>
> Sorry Bernie you misunderstood. This is a way AROUND that limitation.
> The best that I can think of.
>
>  The circumstances are fairly limited to when it would be useful to know
> if a variable has been initialized yet. In those cases, I'm suggesting
> that you could just initialize it to -INF for atoms and integers, and
> INF for sequences and objects. Yes, there are cases where this wouldn't
> work, but they would be extremely rare.
>
> Your program would then consider variables that contain -INF or INF are
> uninitialized.
>
> I know it's not the optimal solution but it's better than none.
>
> It would be next to optimal if NAN had a unique value. Then we could
> have a unique identifier for each uninitialized variable. I don't know
> the nature of NAN though, so I assume it's supposed to be equal to
> everything.
>

A nice try. But it has at least three remaining problems:

  a) It is a manual effort. So if you forget to do it, something will fail
somewhere.

  b) It can't be relied on for use inside 3rd-party library files. IOW, if I
write a library routine that includes a function written like:

      global function xx(sequence s)
           -- check for uninitialized parameter.
           if equal(s,INF) then
              s = ""
           end if
           . . .
      end function

and this library is included by somebody in their program, I cannot rely on
them using the INF convention. And likewise, if I use a somebody else's
library function, I can't rely on them testing for uninitialized values in
this manner.

  c) Unfortunatly, INF is a valid value in its own right, and can be used in
situations other than checking for uninitialized variables.

The problem really needs to be addressed inside the core Eu interpreter. It
knows if a variable is truely initialized or not. The changes are simple.
   - Allow uninitialized variables to be passed as parameters.
   - Create a built-in way of testing a variable's initialization state.

and possibly

   - Create a built-in way of setting a variable's state back to
uninitialized.

This will not break any existing code, and will enable people to write more
robust code.

------------
Derek.