Re: For loops
Bernie Ryan wrote:
>
> CChris wrote:
> >
> > Since there hasn't been much activity on this after some ideas wwere tossed,
> > here would be my proposal for changes/extensions:
> >
> > 1/ Change to the for loop semantics
> >
> > Here would be the new rules:
> > * The loop index of a for loop will be available as a constant after the
> > loop
> > ends, until it is redefined by another for loop or declared as a regular
> > variable.
> > This is a change.
> > * The loop index, if private, can have the same name as any non private
> > symbol,
> > and stops shadowing it on leaving the routine it is defined in. No change
> > here.
> > * The loop index cannot have the same name as a previously declared variable
> > in the same routine (all top level code lumped together counts for a
> > routine).
> > No change here.
> > * The loop index may have the same name as another loop index in the same
> > routine
> > if that other index is not active at the time of its definition. You can
> > thus
> > have two loops with same index following each other, but bot nested in each
> > other. No change here.
> >
> > 2/ New construct
> >
> > for_existing <index>=<start> to <end> [by <increment>] do
> > -- something
> > end for_existing
> >
> > The loop index must be a variable currently in scope and able to be assigned
> > an atom. That variable will not be accessible for write inside the loop,
> > even
> > from a routine called from the loop.
> > If the limit or optional increment are variables, they may be modified
> > inside
> > the loop, but the changes won't affect the limit and increment of the loop.
> >
> > There are no other rules concerning its name, since it is an existing
> > variable.
> >
> > On exiting the loop, its index variable becomes accessible for write again.
> > Incrementing the loop variable will not cause a type check.
> >
> > So this would be like a for loop, but using an existing variable.
> >
> > 3/ Change in ex.err dumps
> >
> > If a variable is defined several times in a scope, like for loop indexes,
> > only
> > the one defined last at the time of the dump will be displayed. This is a
> > change.
> >
> >
> > Expected code breakage:
> > * none for 1/, since the change in 1/ will make legal code that currently
> > isn't.
> > * some (or perhaps none) with 2/: programs which define variable(s) named
> > "for_existing"
> > will require this name be changed.
> > * none for 3/, since code isn't involved.
> > No performance hit is expected.
> >
> >
> > Any comments?
> > Since I expect to move this week, the changes, if agreed upon, won't be
> > committed
> > before next month.
> >
>
> CChris:
>
> The only thing I think might be added to for is continue.
>
I agree that this would be quite useful. Already implemented in AE as "next".
> As far as the the other things that you are talking about
>
> are just not necessary because they all can be handled
>
> simply by using the while loop.
Simply? Well, perhaps.
And for the reader of the code, it is certainly not simpler, since the while
loop is being used for all sorts of different purposes. It's like calling
everything "stuff"; you can handle every sentence simply doing this, and let the
reader guess what you meant.
>
> I think you are concentrating to much on change and complicated
>
> features.
Just some that other users requested.
Definitions of what is simple or not vary among users, so ... it's kind of a
consensus thing.
>
> Just add simple features that do not break code.
>
Did you notice that RDS hasn't followed this pattern in the past? Additionally,
simple features often prove complicated to use - for instance, consider how
little namespaces are used, because they are inadequate out of simplicity.
> Bernie
>
> My files in archive:
> WMOTOR, XMOTOR, W32ENGIN, MIXEDLIB, EU_ENGIN, WIN32ERU, WIN32API
>
> Can be downloaded here:
> <a
> href="http://www.rapideuphoria.com/cgi-bin/asearch.exu?dos=on&win=on&lnx=on&gen=on&keywords=bernie+ryan">http://www.rapideuphoria.com/cgi-bin/asearch.exu?dos=on&win=on&lnx=on&gen=on&keywords=bernie+ryan</a>
CChris
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