Re: Loops (was Re: do { quit; } else { })

On Sun, 11 May 2025 17:30:14 -0700
Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:

Michael S <already5chosen@yahoo.com> writes:
 

On Sat, 10 May 2025 06:43:38 -0700
Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
 

Michael S <already5chosen@yahoo.com> writes:
 

On Sun, 04 May 2025 07:31:11 -0700
Tim Rentsch <tr.17687@z991.linuxsc.com> wrote:
[...]
Also having just one form of loop with pre-condition strikes me as
more elegant.  Since elegance is strongly subjective, I have no
logical arguments in support of me feelings. 

>
In a recent posting I gave some statistics about the three
different kinds of looping controls (while,for,do/while).
do/while loops were almost 20% of all loops, and more than a
quarter of the two kinds of loops other than for().  Besides being
a more pragmatic choice, I think having the three kinds of loops
be distinct in the language is a better choice, because how we
think of the different kinds of loop is different, and it's
helpful to have those differences be readily apparent in the
program, rather than needing to reconstruct them by looking at
code around the loop control fragment. 

>
That sounds like misunderstanding.
I didn't suggest one loop construct.  I suggested two constructs:
for() for loops with pre-condition and do-while for loops with
post-condition. 

 
Yes, I did misunderstand you.  The alternative meaning didn't occur
to me.  I see it now.
 
The same posting I mentioned in the previous response gave while()
loops as occurring more than for() and do/while() combined.  I
conceptualize for() loops quite differently than while() loops, and
vice versa.  By analogy to the only-two-kinds-of-loops suggestion,
the language could forego switch() and provide only if()/else. 

I don't see it as the same or similar. if we compare switch() with if/
if-else/else chain it's clear that switch() helps DRY which is very
important (most important?) principle of programming.
OTOH, while() does not help anything relatively to for().

To
me, neither of those what-might-be-called-simplifications seems like
a good trade.  Have you asked other people to see what their
reactions are?
 
Incidentally, a language change to C was once proposed, so that
a do/while could also have an expression after the while().
Note that this change is backwards compatible with C as it is,
because a simple semicolon after while() is an empty statement.
Adopting this proposal would mean that the language would allow,
for example
 
   do {
      // this part will always be done at least once
      // and once more for each time 'condition' is true
   } while(  condition  ){
      // this part will be done zero or more times
   }
 

That is an interesting idea.
Loops like those do happen quite often in my practice. Of course, if
have to code them as
  for (;;) {
    ...
    if (!condition)
      break;
    ...
  }

I find it probable that proposed extended do-while is somewhat easier
for reader, if for nothing else then because positive logical
conditions tend to be easier to grasp then negative conditions.

allowing a convenient way of writing "loop-and-a-half" type
loops.  Do you have any reaction to this idea?  Suppose
the just plain while() style were eliminated, so ordinary
while() loops would instead be written as
 
   do ; while( condition ){
      // body of while loop
   }
 
Is that better or worse than having a separate while() statement?

I don't think that it's the same. for(;cond;) alternative is less
clumsy and is not even longer than while(cond) in # of characters.

If we compare to newer languages, authors of Go went one step further
and completely gave up on loop with post-condition. Probably for early
70s that was too radical. May be, it is still too radical now. I didn't
write a lot of Go, so can't tell.