On Wed, 9 Oct 1996, Don Stanley <don_stanley@IBM.NET> wrote:

>Its a well accepted and clearly defined and taught axiom of computer >programming in virtually any language that IF an ELSE is available THEN >you use it. I find that the syntax without an else is confusing, and its >impact on efficiency can be enormous .... >I've always been of the opinion that omitting the else is similar to >using goto's. There are ALMOST always good reasons for not doing it.

There have been a few replies to my original post concurring with Don's point above. I simply don't agree that the syntax is confusing where ELSE isn't used - to me, because nesting is only *necessary* in certain cases where the conditions *aren't* mutually-exclusive, the use of nesting when the conditions *are* mutually-exclusive is misleading! (I think to myself 'doesn't the programmer realise those conditions are mutually-exclusive?'). For example, in: if x=1 then do; <action 1> end; else if x=2 then do; <action 2> end; one would summarise the conditions necessary for Action 2 happening as 'action 2 only happens when (x is not 1) and (x is 2)'. The redundancy in this summary is what I think makes this construct logically inferior to sequential IFs.

However, I have already agreed that this is largely a question of personal taste, and of course I agreed in the original post that there are efficiency gains to be had in the wise use of nested IFs.

I think the uses of nesting and goto are quite different cases - the impact on a program of using/not using nesting is largely limited to efficiency, whereas using goto directly and drastically affects the program flow, undermining any attempt to build structure into a program, and is therefore much more dangerous.