Re: FOR NEXT behavior

<news@[EMAIL PROTECTED]
> wrote in message 
news:1189413646.847621.256210@[EMAIL PROTECTED]
> It seems to me that there are five possible ways in which an
> implementation of BASIC might behave in the event of the values in a
> FOR statement being 'inconsistent', any of which could be argued to be
> 'valid'.  In the case of the statement 'FOR i = 3 TO 2' these are:
>
> 1.  Don't execute the body of the loop at all, and leave i unchanged.
>
> 2.  Don't execute the body of the loop at all, but set i to 3.
>
> 3.  Execute the body of the loop once, with i = 3.
>
> 4.  Execute the body of the loop twice, with i = 3 and i = 2.
>
> 5.  Re****t an error.
>
> Personally the one which I consider to be nearest to the 'common
> sense' expectation, and therefore the one I prefer, is (4) i.e. infer
> that the step must be negative.  Given that BASIC statements are
> supposed to be 'English like', and remembering what the 'B' of BASIC
> stands for, this seems best to reflect the 'spirit' of the language.
>
> Failing that, I think my next preference would be (5) - re****t an
> error.  Since arriving at that situation is quite likely to be
> unintended (e.g. a typo) or indicate sloppy thinking (e.g. failure to
> anticipate that it might occur) drawing attention to it seems
> sensible.
>
> Despite them representing what the vast majority of 'real' BASIC
> implementations do, I don't really feel any of (1) to (3) can be
> justified from a 'logical' viewpoint.  (3), which is what BBC BASIC
> does, is the simplest to implement and has the fewest unexpected side-
> effects but that's about all that can be said for it.  (1) and (2) are
> probably quite often 'useful' (that is, they may simplify code) but
> they fail the 'common sense' test quite badly.  Also, the very
> ambiguity over whether the control variable should be changed
> illustrates a flaw.
>
> Richard.
> http://www.rtrussell.co.uk/
> To reply by email change 'news' to my forename.
>
When there are several options, some of which don't give
up much advantage over another, then the remaining advantage
for the users is if it is common with other well used Basics..

As Fred Astaire sang so well, "Let's call the whole thing off".
:-)
jj