Guarding against uninitialized variables RFC

[Jose E. Marchesi]

> Good day everyone,
>
> After 10 days away from almost everything to do with computers in order to
> concentrate on Important Stuff (like beaches), I'm back prodding van
> Vliet's transput.
>
> The open, establish and create procedures will fail with a non-zero return
> code if they cannot establish the linkage between File, Channel, Book and
> the operating system file.  However this can leave the nonpublic Book
> variable in an uninitialized state.
>
> Of course, I can initialize the Book variable to some pattern that I can
> later interpret as meaning no linkage was created; and I can check wherever
> that Book variable is used to make sure it has a valid linkage.
>
> But I don't believe there is a way to detect uninitialized variables other
> than this.
>
> Does anyone have any suggestions?  Thanks in advance!

I think there is no way.

In strict Algol 68 the value actually held by uninitialized variables is
undefined.

In GNU Algol 68 uninitialized variables all have a predictable value: 0
for int, 0.0 for real, " " for char, etc.

But that will not really help to detect uninitialized variables.

I would look to declare a no_book identifier with some distinguishable
value ascribed to it, then get the books initialized to it, then check
for it before accesses.  Alternatively, you could add an additional
book_initialized boolean..